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A Detailed Description of the CLARK Programme

Contents

Introduction (top) (next) (prev)

The Tübingen-Sofia International Graduate Programme in Computational Linguistics and Represented Knowledge (CLARK) will provide a joint teaching and research facility wherein doctoral and master's students primarily from Bulgaria and Central and Eastern Europe (CEE) will pursue their researches in the interdisciplinary field of computational linguistics and knowledge representation. The programme will be based at and draw upon the acknowledged and complementary strengths of its host institutions, the Seminar für Sprachwissenschaft (SfS) of the Eberhard-Karls-Universität, Tübingen, Germany and the Linguistic Modelling Laboratory (LML) of the Central Laboratory for Processing of Parallel Information, Bulgarian Academy of Sciences, Sofia, Bulgaria. The programme will be funded by the Volkswagen-Stiftung.

The education of the students will follow an `apprenticeship' model. That is, the students will pursue their individual researches within a collaborative project-based research environment. The programme will offer graduate students from Bulgaria and CEE the opportunity to pursue their research and education within the broad computational, linguistic, mathematical and philosophical framework necessary nowadays for advanced research in computational linguistics and knowledge representation. The default working language of the programme will be English.

Goals (top) (next) (prev)

Computational linguistics can be viewed in two ways. On one hand, it is the application of various techniques and results from computer science to linguistics, in order to investigate such fundamental problems as what people know when they know a natural language, what they do when they use this knowledge, and how they acquire this knowledge in the first place. On the other, it is the application of various techniques and results from linguistics to computer science, in order to provide such novel products as computers that can understand everyday human speech, translate between different human languages, and otherwise interact linguistically with people in ways that suit people rather than computers. Knowledge representation can likewise be viewed in two ways. On one hand, it attempts to construct mathematical representations of what knowledge is, how it is used, and how it is modified. On the other, it exploits these representations in order to equip computers with simulated intelligence.

Though knowledge representation and computational linguistics clearly address broadly similar research problems, research within each of these fields has hitherto been largely ignorant of research within the other. This ignorance is doubly unfortunate, since interdisciplinary research in knowledge representation and computational linguistics would be likely to yield important scientific advances in the representation, use and acquisition of linguistic knowledge, advances with obvious potential for industrial application in products as diverse as message understanding software, automatic language acquisition devices, user-friendly network navigators, intelligent information retrievers, and machine-aided translation tools. However, the ignorance the two fields have of each other both fosters and is fostered by a wide gulf between the educations received by students of knowledge representation and students of computational linguistics. Attempts to break this vicious circle began in the mid 1980's with the founding of several institutionalised interdisciplinary programmes of education that included computational linguistics and knowledge representation. However, the enormous political and economic changes that occurred at the end of the 1980's meant that such programmes were extremely rare in CEE.

CLARK will be an international programme of graduate education in knowledge representation and computational linguistics, with sites at the SfS in Germany and the LML in Bulgaria. More specifically, the programme will supervise a number of graduate students - primarily from Bulgaria and CEE - and will guide them to the completion of their graduate degrees. All doctoral students to be supported by a CLARK fellowship are expected to complete their doctoral theses during the 24 months of funding that is available to them under the CLARK program. In addition, the CLARK program will produce high-quality teaching materials to be aired and tested at annual CLARK summer schools, the first in Bulgaria and the second in Germany. At the second summer school all doctoral students funded by a CLARK fellowship are expected to present the results of their doctoral thesis research.

Methods (top) (next) (prev)

The CLARK programme will provide a two-site international centre of excellence in computational linguistics and knowledge representation, wherein graduate students primarily from Bulgaria and CEE follow an `apprenticeship' education model by pursuing their individual researches within a collaborative project-based research environment. More exactly, the programme will initiate a small number of research projects in computational linguistics and knowledge representation. Graduate students will then conduct their individual researches while participating in CLARK research projects closely related to their thesis topics. Practical experience at the host institutions of the programme shows that such a combination of individual and collaborative research reduces the sense of isolation typically felt by graduate students working alone, encourages the early presentation of work at conferences and in journals, and provides group-based research experience that is invaluable when students subsequently look for employment.

The ubiquity of knowledge within linguistics provides far too wide a field for us to teach in its entirety. Consequently, we have decided to concentrate on a part of this field that readily exploits our existing expertise. We will teach methods for representing, acquiring and using linguistic knowledge represented as formal theories in feature logics. We do so in the belief that feature logics bestow a number of advantages over existing symbolic approaches to representing linguistic knowledge. By far the most important advantage is that feature logics simultaneously support both linguistic and knowledge representation formalisms. On the one hand, feature logics have been extensively used to support formalisms for various unification grammars such as the Lexical Functional Grammar (LFG) of [Kaplan and Bresnan 1982] (see [Johnson 1988]) and constraint grammars such as the Head-driven Phrase Structure Grammar (HPSG) of [Pollard and Sag 1994] (see [King 1989], [Carpenter 1992] and [Pollard 1998]). On the other, similarities between feature logics and knowledge representation languages have long been recognised (see [Backofen, Trost and Uszkoreit 1991], [Nebel and Smolka 1991], [Manandhar 1993] and [Simov 1995b]). These include set denoting symbols, binary attributes, full Boolean connectivity, and constraints over the domains and ranges of attributes. Such similarities allow us to see feature logics as knowledge representation languages, and to try to equip them with the services necessary for the acquisition and use of linguistic knowledge.

Personnel (top) (next) (prev)

The scientific coordinators of the programme are:
Erhard W. Hinrichs
Seminar für Sprachwissenschaft (SfS)
Eberhard-Karls-Universität
Kl. Wilhelmstr. 113
72072 Tübingen
Germany
eh@sfs.uni-tuebingen.de
Frank Richter
Seminar für Sprachwissenschaft (SfS)
Eberhard-Karls-Universität
Kl. Wilhelmstr. 113
72072 Tübingen
Germany
fr@sfs.uni-tuebingen.de
Kiril Iv. Simov
Linguistic Modelling Laboratory (LML)
Central Laboratory for Processing of Parallel Information
Bulgarian Academy of Sciences
Ave. Acad. G. Bonchev 25A
1113 Sofia
Bulgaria
kivs@bgcict.acad.bg
Hinrichs is professor (C4) of General and Computational Linguistics at the SfS, where he serves as director of the Laboratory for Computational Linguistics. Before accepting the Lehrstuhl at Tübingen, he was employed as a senior research scientist in the Artificial Intelligence Department at Bolt, Beranek and Newman (BBN) Laboratories in Cambridge, Massachusetts, USA, where he contributed to BBN's research projects in knowledge representation and natural language processing. His current research interests include the study of constraint grammar formalisms as a foundation for the representation of linguistic knowledge, natural language processing, speech-to-speech machine translation, the syntax of West-Germanic languages, and the semantics of tense and aspect. His research activities are supported by grants from the Deutsche Forschungsgemeinschaft, the Bundesministerium für Bildung, Forschung und Technologie, and the European Commission. Hinrichs is President of the Foundation for Logic, Language and Information and a member of the Advisory Board and former President of the European Chapter of the Association of Computational Linguistics. As President of the Foundation for Logic, Language and Information (FoLLI) he is involved in the scientific planning of the annual FoLLI-sponsored European Summer School in Logic, Language and Information which offers advanced training to students from Eastern and Western Europe.

Simov is a research fellow at the LML, where he helped to create several large morphological dictionaries of Bulgarian (see [Simov et al. 1990], [Simov et al. 1992], [Simov and Popov 1996] and [Popov, Simov and Vidinska 1997]), and lead two research projects concerned with knowledge representation (see [Simov and Boynov 1994] and [Simov 1997]). His current research interests include logic-based knowledge representation languages (terminological and feature logics, Conceptual Graphs, the Knowledge Interchange Format (KIF), and the Knowledge Query and Manipulation Language (KQML)), knowledge acquisition and reuse, natural language processing systems (grammar engineering, acquisition of linguistic knowledge, morphology, HPSG), and adaptive user interfaces. His expertise in knowledge representation includes using SRL as a knowledge representation language (see [Simov 1995b]). His work with morphological grammars and dictionaries has given him considerable practical experience in the management of very large linguistic knowledge bases. Moreover, King and Simov have successfully worked together for some time on a variety of research topics, including the complexity of SRL modelability (see [King, Simov and Aldag 1998]) and the management of knowledge represented as SRL theories (see [King and Simov 1998]).

Resources (top) (next) (prev)

The programme will draw heavily upon the strengths of its host institutions. The SfS is a seminar within the Neuphilologie Fakultät of the Eberhard-Karls-Universität. It was founded in 1992 in order to teach and research general linguistics in an interdisciplinary environment that includes not only linguistics but also computer science, philosophy, psychology and mathematics. In addition to offering master's programmes in both general linguistics and general linguistics with a subsidiary subject, and hosting a Graduiertenkolleg ``Integriertes Linguistik-Studium'' that offers a doctoral programme in integrated linguistic studies, the SfS is engaged in numerous research projects, including several projects within Sonderforschungsbereich 340 (SFB 340) ``Sprachtheoretische Grundlagen für die Computerlinguistik'' funded by the Deutsche Forschungsgemeinschaft.

The central idea of SFB 340 is to make insights and results of linguistic theories utilisable for the development of computational linguistics. Research concentrates on the requirements and standards which have to be fulfilled in order to successfully integrate structural descriptions of linguistic phenomena and algorithmic realisations of linguistic processes within the development of language-understanding and/or language-generating systems. Altogether, SFB 340 consists of fifteen subprojects, seven of which are located in Tübingen. The range of subjects includes theoretical syntax and semantics as well as their application in automatic text analysis.

The Graduiertenkolleg ``Integriertes Linguistik-Studium'', associated with the Seminar für Sprachwissenschaft, is a graduate school for interdisciplinary language-related studies funded by the Deutsche Forschungsgemeinschaft and located in Tübingen. The Graduiertenkolleg focuses on the interface of theoretical and computational linguistics with computer science, philosophy of mind, logic and linguistic studies of individual languages (particularly Slavic, Romance and Germanic languages). It is expected that there will be significant collaboration between the twelve doctoral and two post-doctoral fellows of the Graduiertenkolleg with the advanced training and research measures outlined in the current proposal.

The LML is a research institution within the Bulgarian Academy of Sciences where projects are in progress on natural language processing (ranging from the semantics of affixes to the syntactic and semantic analysis of sentences and texts), formalisms for knowledge representation, and large computer dictionaries. Also, the LML has enjoyed a long association with the St. Kliment Okhridski University, Sofia, Bulgaria whereby members of the LML give courses in knowledge representation and natural language processing, and supervise master's students, and students participate in the projects of the LML.

Both the SfS and the LML have a good record of participation in international research collaborations. For example, the SfS and LML are individually partners in a number of East-West European collaborative projects funded by the European Union Copernicus initiative. Such projects include

TELRI: Trans-European Language Resources Infrastructure. Goal: to create a viable network between leading language and language technology centres in Europe in order to provide a neutral platform where public domain language resources and expertise in language technology are built up, made available and disseminated. Partners: 22 university and academic institutions including the LML.

GLOSSER. Goal: to apply language processing techniques - morphological processing and corpora analysis - to computer-assisted language learning (CALL). Partners: Gröningen University, The Netherlands; Rank Xerox Research Centre, France; Morphologics, Hungary; Tartu University, Estonia; LML.

BILEDITA: Bilingual Electronic Dictionaries and Intelligent Text Alignment. Goal: to provide a uniform dictionary format for existing electronic dictionaries, to create a uniform lexical encoding scheme in terms of both form and content of the lexical entries, and to elaborate a uniform morphological model. Partners: München University, Germany; University of Paris 7, France; University of Warsaw, Poland; TOO Information Systems and Technologies Ltd., Russia; LML.

STEEL: Developing Specialised Translation/Foreign Language Understanding Tools for Eastern European Languages. Goal: to extend the functionality of existing translation aid tools to languages of CEE (Czech and Polish) with a special interest in providing translation assistance for technical and specialised documentation. Partners: Rank Xerox Research Centre, France; Université Louis Lumière, France; Charles University, Czech Republic; Moravia translations a.s., Czech Republic; University of Warsaw, Poland; Lexis, Poland; SfS.

In addition, the SfS will be a partner in a future project ``Extending Computational Grammars by Learning'' funded by the European Union Training and Mobility for Researchers (TMR) initiative. Though not an East-West European collaboration, both the overall aim of the TMR project and several of its individual subprojects - particularly the SfS-based ``Feature Estimation'' subproject concerned with estimating parameters in stochastic feature logics - are of great relevance to the CLARK programme. Even more relevant to the CLARK programme are the fruitful research collaborations the SfS and LML have already enjoyed. Via several visits by Simov and Nevelin Boynov to the SfS and by King to the LML since March 1994, a close working relation has developed, culminating in a number of published papers and the port of a natural language processing system.

In addition to collaborative research, both host institutions are eager to support international graduate education. For example, the SfS, via the Tübingen office of the International Centre (IC), has taken an active interest in the harmonisation of doctoral education in East and West Europe by actively seeking to implement the policy document ``IC Programs for Ph.D. Students'' that arose in part from the Volkswagen-Stiftung funded ``IC Conference on Training of Ph.D. Students'' in Budapest, 1995. This is reflected in several IC sponsored visits to the SfS by East European scholars (including three visits by Simov), and the hosting of the Volkswagen-Stiftung funded ``IC Workshop on Computational Linguistics'' in 1996. Though the CLARK programme is not strictly part of the IC initiative, we enjoy excellent relations with the IC Tübingen office, and both we and the IC see the CLARK programme as a test implementation of several key recommendations of ``IC Programs for Ph.D. Students''.

Benefits (top) (next) (prev)

The CLARK programme has a number of benefits for students and academics in Bulgaria and CEE. Firstly, and by far most importantly, the programme will enable a small number of doctoral students to attain their doctoral degree and in the process pursue their education within the wide computational, linguistic, mathematical and philosophical environment needed to prepare them for top-level research in computational linguistics and knowledge representation. Secondly, the programme will help to safeguard, at least for the small number of students funded by CLARK, the natural line of academic development from undergraduate, through graduate student, to junior researcher that is currently at great risk in Eastern Europe. Thirdly, the programme will provide students, lecturers and researchers with both affordable access to first-rate instruction materials, and the chance to participate in high-calibre international research projects. Finally, the programme will further the eastward transfer of a number of novel ideas - including constraint grammars, feature logics and knowledge representation languages - with the hope of achieving a `critical mass' of academics in Sofia that will serve as a focus for those disparate and isolated workers that currently teach and research these fields in Eastern Europe. In addition, the CLARK programme offers some secondary benefits to the host institutions. For the SfS, the programme will broaden the base of graduate education the SfS currently provides by complementing the existing Graduiertenkolleg with an overtly international graduate programme. For the LML, the programme will not only help to protect the existing research and teaching potential, but also provide equipment that will ensure the LML can continue to conduct intensive research and teaching in computational linguistics and knowledge representation.

Existing Work (top) (next) (prev)

Both the SfS, with its associated SFB 340 participation and Graduiertenkolleg, and the LML, with its extensive expertise in large linguistic knowledge bases, constitute existing centres of excellence in their own right. Indeed, the resources that the SfS and the LML offer the CLARK programme are in many respects complementary. On one hand, the SfS enjoys an acknowledged top-flight reputation for teaching and research in feature logics, their computational implementation, and their use to express constraint grammars, notably HPSG grammars of German. On the other, the LML has considerable expertise in knowledge representation, and has used that expertise to amass an impressive body of large linguistic knowledge bases. Together, the SfS and LML have already produced, both individually and collectively, a large body of research and teaching materials that are directly relevant to the CLARK programme. Here we summarise some of the more important examples of these materials.

Research (top) (next) (prev)

A key feature of the `apprenticeship' model of education that we envisage for the programme is a number of collaborative research projects in which students of the programme participate. Consequently, the success of the CLARK programme rests as much upon the research as the pedagogic abilities of the scientific coordinators, since students will obtain maximum educational benefit from taking part in research projects only if the projects are innovative enough to provide good thesis topics, interesting enough to thoroughly engage the students, important enough to establish the reputation of the students within the wider research community, and demanding yet supportive enough to stretch the students without breaking them. The research projects of the programme will of course to some extent reflect the existing research expertise of the scientific coordinators. This expertise includes the following.
Speciate Reentrant Logic.
[King 1989] - King's doctoral dissertation, written at the Department of Mathematics of the University of Manchester, Manchester, England under the supervision of Peter Aczel - introduced SRL and used it to support a formalism for HPSG. Working within the HPSG framework of [Pollard and Sag 1987], [King 1989] suggested many innovations (such as using formulae of a feature logic rather than feature structures as descriptions of linguistic objects, and partitioning the linguistic universe via a set of maximally specific sort symbols) that have become part of the HPSG orthodoxy with the publication of [Pollard and Sag 1994]. King's subsequent research on SRL - carried out with others at the CSLI and the SfS - followed two broad lines.

The first line addressed the philosophical repercussions of formulating linguistic theories as formal theories in a feature logic, and considered such fundamental questions as what is it for a theory to be true, how might the truth of a theory be subject to experimental verification or falsification, and what is the ontological status (if any) of a theory. Interim results appeared in [King 1994a] and a number of conference presentations, but personal misgivings about the philosophical adequacy of the results lead King to research further rather than publish [King 1994a]. This research has since borne fruit in [King in prep].

The second line studied the mathematical properties of SRL. [King 1989] presented a logic for SRL entailment and showed that this logic is sound and complete. Stephan Kepser, then of the SfS, showed in his master's thesis [Kepser 1994] that the logic was also decidable. The philosophical research undertaken for [King in prep.] unearthed a number of important relations in SRL - including modelability, existential prediction and universal prediction - that were subsequently explored mathematically. For example, Bjørn Aldag of the SfS showed in his master's thesis [Aldag 1997] that no finitary, sound and complete logic for existential prediction can exist, and [King, Simov and Aldag 1998] established that co-r.e. completeness is a least upper bound (though not a lower bound) on the complexity of modelability.

Troll, MacTroll and ConTroll.
From 1992 to the present, Hinrichs lead SFB 340 project B4 ``Constraints on Grammar for Efficient Generation'' at the SfS. In order to provide an accurate test bed on which to mount and evaluate various language generation techniques, King provided the mathematical basis (see [Gerdemann and King 1994] and [King 1994c]) for Dale Gerdemann and Thilo Götz of B4 to build an SRL-based and Unix-platformed processing system called Troll with which to accurately implement HPSG theories of linguistic phenomena known to be problematic for generation (see [Hinrichs et al. 1994]). Boynov of the LML created MacTroll, a port of Troll to the Macintosh platform.

Though built with accuracy more than efficiency in mind, Troll proved to be a surprisingly good system, performing as well as other HPSG implementation systems on the market. Consequently, B4 won funding for not only a new 3 year term, but also a sister project B8 ``An HPSG-Fragment for German''. Götz has since developed a constraint-logic programming successor ConTroll to Troll (see [Götz and Meurers 1997a] and [Götz and Meurers 1997b]), and B8 has both written a large German fragment in pure HPSG fashion as a formal theory in an extension of SRL (see [Hinrichs et al. 1997]) and implemented this theory using ConTroll (see [Courbet et al. 1997]). This theory is an invaluable resource for the programme, since it constitutes a large body of linguistic knowledge that is already represented as a feature-logic theory and implemented as a constraint-logic program.

German Syntax in Head-Driven Phrase Structure Grammar.
In joint research with Tsuneko Nakazawa of the University of Tokyo, Tokyo, Japan, Hinrichs has studied various syntactic and semantic phenomena of German in the HPSG framework, including topicalisation (see [Hinrichs and Nakazawa 1997a]), auxiliary fronting (see [Hinrichs and Nakazawa 1989] and [Hinrichs and Nakazawa 1994]), infinitival complementation (see [Hinrichs and Nakazawa 1997b]), relative clause constructions (see [Hinrichs and Nakazawa in prep.]), and complex predicates (see [Hinrichs, Kathol and Nakazawa 1997]).

As principal investigator of SFB 340 project B8, Hinrichs oversees the specification and implementation of a core grammar fragment of German which includes all major syntactic constructions of German and puts special emphasis on adequate linguistic analyses of constituent questions, parentheticals, and verbal clusters.

Declarative Knowledge Representation Languages.
From 1994 to 1996, Simov lead two projects at the LML on logic-based declarative knowledge representation languages, both funded by the Bulgarian Ministry of Education and Science and the Eureka Fund.

The first project researched methodologies for establishing semantic correspondences between knowledge bases represented in various knowledge representation languages (see [Simov 1995a]). This methodology was then applied to the problem of using the ACLRN knowledge representation language as a query language for relational databases. The problem was overcome by building an ACLRN knowledge base together with a semantic correspondence between the terminological part of the knowledge base and the relational schemata of the relational database (see [Popova 1994]).

The second project constructed an explicit representation of the control of inference procedures in implementations of declarative knowledge representation languages. This representation allows an expert in some knowledge domain to encode control information to suit specific tasks over that domain. The project developed a special normal form for SRL theories - construed as knowledge bases - and an indexing technique over such normal forms (see [Simov 1997]). The indexing technique enables the automatic reordering of a theory so that the theory exhibits certain relations between elements of the knowledge represented by the theory. The indexing technique also supports the reorganisation of a theory to suit those requirements of a user that are based on knowledge that is not represented by the theory, such as the environment in which the theory is to be used and the type of problem to be decided.

Morphological Grammars and Dictionaries.
From 1988 to 1993 and from 1995 to 1997, Simov was involved in two different projects at the LML to develop morphological grammars of the Bulgarian language with large morphological dictionaries. The projects took different approaches to the acquisition of linguistic knowledge.

The first approach classified lexical items with respect to a set of morphological classes. The classification itself was done by means of an index over the morphological classes, such that a lexicon writer need only provide minimal information about a particular word in order for it to be correctly classified. In addition to the index, an editor was built to enable checking and editing of the morphological class to which a target word is assigned. The project constructed a Bulgarian dictionary with 32 000 entries and a module for the analysis and synthesis of wordforms (see [Simov et al. 1990] and [Simov et al. 1992]). The system was also applied to Russian nouns, adjectives and verbs, and German nouns.

The second approach automatically constructed a Bulgarian morphological dictionary by extracting the relevant linguistic knowledge about the morphological classes of words from two machine-readable dictionaries. Starting with a minimal grammar of Bulgarian word formation - sufficient to analyse the information in the two machine-readable dictionaries - the project arrived at a complete morphological grammar and a morphological dictionary with 75 000 entries (see [Simov and Popov 1996] and [Popov, Simov and Vidinska 1997]), which together can be used as the morphological component in a system to automatically process the Bulgarian language.

Knowledge Management.
In 1995, King and Simov began to research ways to equip SRL - construed as a knowledge representation language - with the computational services necessary to manage represented knowledge. In particular, in a natural outgrowth of Simov's work hand-constructing indices to morphologically classify Bulgarian words (see above), King and Simov researched the automatic deduction of classificatory systems from SRL theories, where a classificatory system comprises (i) a classification, a set of labels that indicate sets of objects, and (ii) an index, an algorithm that computes from limited information about an object the label of the class to which the object belongs.

Classificatory systems are widespread in linguistics. For example, consider the declension of German nouns. Each German noun has eight declensions, a singular and a plural declension for each of the cases nominative, accusative, genitive and dative. The declension of each German noun can be classified according to how its nominative singular declension is modified by affixation and umlauting, and almost all German nouns exhibit one of a small set of patterns. This set of patterns constitutes a classification in which each pattern is a label that indicates the class of German nouns whose declensions exhibit the pattern. There is also an index, since the nominative singular, genitive singular and nominative plural declensions of almost all German nouns determine all their declensions. Indeed, all German dictionaries exploit this index, in that each entry for a noun gives only its nominative singular, genitive singular and nominative plural declensions.

Typically, the deduction of a classificatory system from a linguistic theory is done by hand. However, hand-crafting a classificatory system is time consuming, a very significant factor in, say, machine translation, where different classificatory systems for several languages may be required. Moreover, a hand-crafted classificatory system risks unwittingly violating the theory from which it is deduced, with potentially disastrous consequences, as, say, the classification wrongly conflates two distinct classes, or the index puts some linguistic objects into inappropriate classes. For these two reasons alone, a device that effectively generates an accurate classificatory system from a general linguistic theory would be very beneficial to computational linguistics. In [King and Simov 1998] we showed that there exists a device to automatically deduce a classificatory system from a finite SRL theory.

Supervision (top) (next) (prev)

The principal duty of the scientific coordinators must be the supervision of graduate students within the `apprenticeship' model. The following indicates the considerable experience in such supervision the scientific coordinators have already accrued, by giving a selection of master's theses in CLARK related topics that they have supervised within this model. (Ger) indicates that the thesis was submitted to the Neuphilologie Fakultät, Eberhard-Karls-Universität, Tübingen, Germany, while (Bul) indicates that the thesis was submitted to the Faculty of Mathematics and Computer Science, St. Kliment Okhridski University, Sofia, Bulgaria.
Bjørn Aldag.
A Proof Theoretic Investigation of Prediction in HPSG. 1997. This thesis motivates the desirability of a sound and complete calculus for the prediction relations of [King in prep.], but goes on to demonstrate that such a calculus is logically inconceivable for existential prediction. (Ger)
Natali I. Alt.
A Typed Feature Logic with Set-valued Attributes as a Foundation for LP Rules. 1996. In the context of a specific treatment of linear-precedence rules, this thesis incorporates set-valued features into an equality-free feature logic, and provides a decision algorithm for satisfiability in this logic. (Ger)
Thilo Götz.
A Normal Form for Typed Feature Structures. 1994. Building upon the resolved feature structures of [King 1994c], this thesis uses the syntactically determined notion of redundant arcs to arrive at a normal form (with appropriate translation) for feature structures that is semantically transparent, representationally compact, and inferentially efficient. (Ger)
Stephan Kepser.
A Satisfiability Algorithm for a Typed Feature Logic. 1994. This outstanding thesis shows that satisfiability in SRL is decidable, and hence that SRL itself is decidable. (Ger)
Atanas Kiryakov.
An Ontology-based Translation of Knowledge. 1995. An ontology of the logical basis of SRL was developed by means of KIF in order to translate logical theories represented in SRL to other Typed Feature Logics. The ontology allows translations from other typed feature logics into SRL if the theories represented in these logics can be translated into KIF using the primitives of the ontology. (Bul)
W. Detmar Meurers.
On Implementing an HPSG Theory: Aspects of the logical architecture, the formalisation, and the implementation of Head-driven Phrase Structure Grammars. 1994. This thesis is a case study of the practical implementation of HPSG grammars and lexicons under various formalisms and upon various implementation platforms. (Ger)
Maria P. Popova.
The Kl-One Knowledge Representation Language as a Query Language to a Relational Database. 1994. A mechanism for establishing a correspondence between the terminological part of a knowledge base in the Kl-One-like knowledge representation language ACLRN and the conceptual scheme of a relational database was developed in order to use the terminological knowledge base to query the database. (Bul)
Frank Richter and Manfred Sailer.
Remarks on Linearization: Reflections on the treatment of LP-rules in HPSG in a typed feature logic. 1995. This thesis presents a general SRL-based architecture for treating word-order phenomena in natural languages in HPSG, with two detailed and extensive examples concerning word order in the German Mittelfeld. (Ger)

Teaching (top) (next) (prev)

Since the annual CLARK summer schools are an important component of the programme, not least for encouraging the enrolment of new graduate students on the programme, the pedagogic abilities of the scientific coordinators must include not only the personal instruction inherent to the supervision of graduate students, but also the `blackboard and chalk' instruction inherent to teaching in a lecture theatre, as well as the ability to produce and amass high-quality teaching materials. The following lists several CLARK relevant courses that scientific coordinators have taught as university and/or summer school courses, with existing teaching materials where available.
Formal Syntax: the study of German in Head-Driven Phrase Structure Grammar.
Hinrichs has taught several courses in computational linguistics and theoretical linguistics for undergraduate and graduate students at the SfS and elsewhere. These include
Introduction to Head-Driven Phrase Structure Grammar: This introductory course focused on the mathematical, computational and linguistic aspects of the theory of HPSG. It included a comparison between typed feature logics and knowledge representation formalisms such as Kl-One, and emphasised the constraint-based approach to representing linguistic knowledge inherent in HPSG.

Advanced Research Seminar on Head-Driven Phrase Structure Grammar: This course is offered on a regular basis for graduate and advanced undergraduate students. In the past it has been co-taught by Tilman Höhle of Tübingen University, Paola Monachesi now of Utrecht University, Utrecht, The Netherlands, and Carl Pollard of the Ohio State University, Columbus, Ohio. USA. Topics have included the study of German and Romance Languages in HPSG, the syntax-semantics interface, logical foundations of HPSG (with contributions from King), extensions to the expressivity of HPSG's constraint language (with contributions from Frank Richter and Manfred Sailer of the SfS), as well as computational aspects of HPSG (with contributions from Dale Gerdemann, Thilo Götz and Detmar Meurers of the SfS).

Implementation of HPSG Grammar Fragments in ConTroll This course offered hands-on experience to advanced students who are interested in the formalisation of linguistic knowledge in the ConTroll system. The course introduced the theoretical concepts and implementational realisation of the main ingredients of constraint grammars: highly structured lexical representations, constituent structure, and the encoding of well-formedness constraints on grammatical representations. The course combined background lectures with hands-on laboratory sessions. The lectures focused on HPSG, but included a comparison to other constraint and unification grammar formalisms (such as LFG and Extended Categorial Grammar).

Mathematical Logic.
King has taught several mathematical logic courses at the SfS, on various topics and at various levels. These include
Mathematical Logic for Students of the Humanities: This introductory course taught mathematical logic to students with a background in the humanities. Assuming only arithmetic (not set theory), the course covered the syntax and semantics of propositional logic, the soundness and completeness of propositional logic, the syntax and semantics of countable first-order predicate logic, and the soundness and completeness (sketched) of countable first-order predicate logic.

Set Theory and Mathematical Logic: This advanced course taught set theory and mathematical logic to students with some background in mathematics. The set theory part of the course covered Frege set theory, the class paradoxes, the class/set distinction, basic axiomatic set theory (the existence, pair, union and replacement axioms), ordinals and cardinals, the infinity axiom and its independence, ordinal and cardinal arithmetic, the choice axiom and well ordering, the power axiom and Cantor's theorem, and the foundation axiom and Zermelo-Fraenkel set theory. The mathematical logic part of the course covered the syntax and semantics of first-order predicate logic, the soundness, completeness and compactness of first-order predicate logic, Löwenheim and Skolem's cardinality theorems, Gödel's incompleteness theorems, and Herbrand's theorem and logic programming.

Recursion Theory: This introductory course taught recursion theory to students with mixed backgrounds in linguistics and computer science. The course covered Turing machines, semi-Thue systems, equivalences between the two, decidability and undecidability, diagonalisation and pumping techniques, and the Chomsky hierarchy.

Lecture notes or highly recommended text books exist for all of these courses.
Feature Logic.
In addition to general mathematical logic, King has taught a number of more advanced and specialised courses on feature logics at the SfS. These include
From Unification to Constraint: This advanced course taught a variety of formalisms for HPSG to students with mixed backgrounds in mathematics, computer science and linguistics. The course covered unification formalisms in which algebraic operations are used to construct models of complexes of partial information about linguistic objects, Carpenter feature logic formalisms in which formulae are used to denote models of complexes of partial information about objects, and King feature logic formalisms in which formulae are used to denote sets of objects. A short (5x2 hours) version of this course was presented at the 8th European Summer School in Logic, Language and Information, Prague, the Czech Republic, 1996.

Speciate Reentrant Logic. This advanced course taught SRL and its HPSG applications to students with mixed backgrounds in mathematics, computer science and linguistics. The course covered the syntax and semantics of SRL, the soundness and completeness of SRL, the `junk slot' encoding of relations, expressing HPSG grammars as SRL theories, linguistic truth and exhaustive models, and tokens, types and feature structures.

Lecture notes exist for all of these courses, including the short summer school course. The lecture notes for the SRL course are being rewritten for publication as [King in prep.].
Declarative Knowledge Representation Languages.
Simov, together with Atanas Kiryakov of the LML, has taught an advanced course on declarative knowledge representation languages construed as sublogics of first-order predicate logic to students of the Faculty of Mathematics and Computer Science, St. Kliment Okhridski University, Sofia, Bulgaria. The course covered Kl-One knowledge representation languages, SRL, Conceptual Graphs, and KIF. The main goal of the course was to show the similarities between these logic-based knowledge representation languages, the differences between them being mainly due to the different tasks to which they are applied. Lecture notes (in Bulgarian) exist for the course.

Proposed Work (top) (next) (prev)

During the programme, the scientific coordinators will lead several research projects on which graduate students will collaborate, supervise a number of graduate students pursuing project research alongside related thesis research, and organise annual summer schools in which the programme disseminates its work and attracts new graduate students. Here we briefly outline the work we will pursue.

Research (top) (next) (prev)

The essence of the `apprenticeship' model is to provide a number of research projects that serve as environments in which graduate students conduct collaborative project research alongside their individual project-related thesis research. Such a combination of individual and collaborative research reduces the sense of isolation typically felt by graduate students working alone, encourages the early presentation of work at conferences and in journals, and provides group-based research experience that is invaluable when students subsequently look for employment. The success of this model has already been demonstrated at the SfS and LML, producing several excellent theses and outstanding young researchers.

As mentioned earlier, the scope for applying knowledge representation techniques to linguistics is too broad for the programme to cover in its entirety. Consequently, the programme will offer projects that exploit the existing research strengths of the scientific coordinators in representing, acquiring and using linguistic knowledge represented as formal theories in feature logics. Examples of suitable projects include the following.

Extending SRL.
Though [King 1989] created SRL to support a formalism for HPSG, SRL is an extremely simple and versatile logic that can be extended to apply to a number of knowledge domains beyond HPSG. We will extend SRL to suit three specific domains chosen for their utility and variety.
Head-driven Phrase Structure Grammar: HPSG grows ever more sophisticated, making new demands of its underlying formalism. Though SRL was created to deal with the most fundamental aspect of an HPSG formalism, namely the classical interpretation of descriptions, the logic has been surprisingly adept at handling these new demands. For example, accounts within SRL have been made of such HPSG exotica as linear precedence (see [Richter and Sailer 1995]) and lexical rules (see [Meurers and Minnen 1997]). Nonetheless, we will develop SRL in order to ensure that it stays abreast of the formal requirements of the most recent advances in HPSG. For example, the ability to recursively define relations among objects is unquestionably one of the most pressing of these requirements. While SRL has hitherto been able to encode all such definitions using so-called ``junk slots'', this technique is both extremely counterintuitive and cumbersome. Better would be an elegant and general method for recursively defining relations that can either be compiled into SRL, or, if necessary, expressed within a properly stronger extension of SRL. Research on such an extension has already begun between King and Simov, and Frank Richter and Manfred Sailer of B8, in order to facilitate B8 in formalising an HPSG account of a large German fragment as an SRL theory. This research has already yielded a tentative specification for Relational SRL (RSRL). We will continue this work and arrive at either an embedding of RSRL in SRL or a well understood logic for a properly more expressive RSRL.

Corpus Linguistics: The computational linguistics research community suffers from a number of sharp divisions over approaches to the problem of computationally implementing natural language, such as ``symbolic'' versus ``neural'', ``deterministic'' versus ``stochastic'', and ``theoretical'' versus ``corpus based''. Collaboration across these divides is relatively rare, to the detriment of the entire research community. However, recent times have seen an increase in the number of journals and conferences calling for ``hybrid'' approaches to computational linguistics that bring together hitherto disparate research traditions. By virtue of SRL, HPSG based upon SRL stands in the ``symbolic + deterministic + theoretical'' tradition. However, we will undertake research to bridge the ``theoretical'' versus ``corpus based'' distinction. [Lager 1996] extended the Prolog computer language to include sufficient mark-up features that corpus linguistics can be performed within a formal framework suitable for theoretical linguistics. We will similarly extend SRL, so that theory- and corpus-based linguistics can be performed within a single formal language better suited to linguistics than Prolog. We have picked this divide to bridge because linguistic corpora represent a vast source of linguistic facts that could be used to automatically construct huge linguistic knowledge bases, provided the facts can be extracted in some way. For example, given an SRL with mark up capabilities, a [King and Simov 1998] device for this extended SRL, and good corpus analysis software, the device could readily work in tandem with the corpus-analysis software to automatically digest large corpora and classify the words (or any other suitable target linguistic item) in the corpora.

Description Logics: Kl-One-like knowledge representation languages have been successfully used to represent extralinguistic knowledge in several natural language processing systems (see [Franconi 1994] and [Quantz et al. 1995]). In order to represent such knowledge in SRL without the need for an interface to an external knowledge representation system, we will extend SRL to include relational attributes, general conditions on a type hierarchy, number restrictions and an object level. (Notice that Natali Alt of the SfS has already added relational attributes to SRL in her master's thesis [Alt 1996].) These extensions would allow easy conversion to SRL theories of existing knowledge bases represented in certain Kl-One-based systems.

Tailoring Classificatory Systems.
[King and Simov 1998] identified five qualities that experience has shown a classificatory system deduced from an SRL theory should possess: (Q1) each pair of distinct labels in the classification should indicate inherently disjoint sets of objects; (Q2) no label in the classification should indicate an inherently empty set of objects; (Q3) the labels of the classification should indicate sets of objects that are neither too narrow nor too broad; (Q4) the index should correctly assign each object the label of the class to which the object belongs; and (Q5) the index should efficiently assign each object the label of the class to which it belongs. [King and Simov 1998] addressed only qualities (Q1), (Q2) and (Q4) in order to establish that automatically generating a classificatory system from a general linguistic theory is at all possible. However, it is qualities (Q3) and (Q5) that provide the means to tailor the output of the device so that the classificatory system it produces is an accurate formal rendition of the user's intuitions concerning the classification of objects in a given linguistic domain. We will equip the [King and Simov 1998] device with formal mechanisms that achieve qualities (Q3) and (Q5).

Tailoring a classificatory system involves changing the granularity of the classes in the system to ensure that the classification truly captures the intuitions of the theory from which it is deduced. Some of the classes produced by the [King and Simov 1998] device can be too general for the linguistic task at hand, while others can be too specific: sometimes it is necessary to make fine distinctions between very specific classes, sometimes it is necessary to allow very general classes. A possible solution to the first problem is for the device to produce not a classificatory system but a classificatory hierarchy built upon a classificatory system, as suggested in the conclusion of [King and Simov 1998]. The second problem can be solved by allowing the user to specify new constraints either on the whole classificatory system or on part of it (via a classificatory hierarchy). These new constraints can be of two forms: low-level constraints imposed when the user wishes to globally change an entire theory; and high-level constraints imposed when the user wishes to locally change specific classes that agree with knowledge already represented by a theory. The new constraints can be achieved by extending the [King and Simov 1998] device.

The [King and Simov 1998] device comprises three algorithms, Class, Index and Clause. The Class algorithm deduces a classification from a finite SRL theory. The Index algorithm deduces an index tree - a finite tree-like structure comprising queries and possible responses to them - from a classification. The Clause algorithm subsequently classifies objects on the basis of the responses of a human or computer oracle to queries read from the index tree by Clause. However, the queries in an index tree need not be those most appropriate to pose to a given oracle. To overcome this problem we must impose additional constraints on which queries can occur in an index tree. If the oracles understand sufficient of the input theory then the problem can be solved by modifying Index to construct, where possible, index trees that comprise only queries from a predefined set of queries. However, if the oracles understand insufficient of the input theory then the problem can be solved by constructing a semantically equivalent theory that the oracles can understand, together with a `translation' between the theories.

The Clause algorithm queries an external oracle in order to elicit sufficient information to classify an object. However, certain inferential processes, such as parsing and generation, themselves pose queries, but to a classification, in order to further instantiate their current information about some objects. [Simov 1997] developed a new indexing technique that involves all of the information in an SRL theory. This indexing technique allows automatic reordering of the evaluation of a query with respect to a theory. It also allows the representation of expert knowledge. We will extend this work in several directions. Firstly, we will extend the current technique to cover the extensions of SRL described earlier. Secondly, in order to use the huge volume of existing natural language text corpora as a source of control information, we expect to incorporate a stochastic mechanism to evaluate the success or failure of an inferential process with respect to a given task and set of texts. Thirdly, we will combine this indexing technique with the modularisation technique of [Simov 1995a] in order to allow the extraction of relevant optimal theories with respect to given tasks. For example, extracting the relevant morphological knowledge and data from a rich morphological grammar and dictionary in order to support a spell checker requires the development of a simplified morphological theory and an appropriate control strategy with respect to the problem of spell checking.

Abduction and Reclassification.
The revision of a linguistic theory naturally arises during its development. Replacing an old theory with a new theory can create a severe problem if the [King and Simov 1998] device is being used to deduce a classificatory system from that theory. Must all of the objects already classified under the classificatory system deduced from the old theory be reclassified under the different classificatory system deduced from the new theory? We will equip the [King and Simov 1998] device with a reclassification procedure to help reclassify already classified objects under a new classificatory system with minimum effort.

The problem of reclassification is to find - for each object classified under an old classificatory system - the new class it occupies under the new classificatory system. In order to minimise the information needed to reclassify objects, the system must find the differences between the new and old classificatory systems and establish appropriate correspondences among the new and old classes. Once the correspondences are established the system can query an external oracle for additional information about those objects for which the system has insufficient information to reclassify automatically. We are currently considering a process in which the Index algorithm of the [King and Simov 1998] device is directed to construct an index tree that comprises old queries, where possible, so that the Clause algorithm can then take advantage of information already present in the old classification.

Note that classifying objects using a classificatory system can itself indicate changes to the linguistic theory from which the classificatory system was deduced. For example, suppose that a linguistic object cannot be properly assigned a class via the index of a classificatory system. This indicates a fault not with the classificatory system but rather with the theory from which the system was deduced. Simply put, the theory overlooked the object. Clearly, the theory must be modified to accommodate the object, but several problems arise in such a circumstance. What of the existing theory can remain unchanged, and what must be modified? What should those modifications be? We will equip the [King and Simov 1998] device with an abduction mechanism offering appropriate changes to the input theory.

Abduction is an inference rule that modifies a theory in order to accommodate an observation that is at variance with the original theory. Since abduction is known to be unsound, we cannot expect it to work correctly when unconstrained. We will therefore investigate constrained and supervised abduction within a hierarchy of theories, such that an application of abduction to explain an observation at variance with the hierarchy prefers to modify theories low in the hierarchy. For example, suppose that a lexicon writer is constructing a morphological dictionary with respect to a given morphological grammar. The dictionary must be consistent with the grammar. In addition, the morphological grammar must be consistent with universal grammar and possibly other grammars, such as a syntactic grammar or a semantic grammar. If the lexicon writer finds a new morphological fact that conflicts with the morphological grammar then the abduction rule would offer one or more explanations of this fact within the morphological grammar but not within the other grammars.

The way a theory is modified strongly influences reclassification. If the modification is due to an application of an abductive rule within the [King and Simov 1998] device then the reclassification procedure has full knowledge about the modifications to the theory, and can thus build the correspondences between the old and new classifications automatically. But if the modification is external to the device then the reclassification procedure has limited knowledge about the modifications, and must thus consult an external oracle in order to find the right correspondences.

Supervision (top) (next) (prev)

The goal of the CLARK programme is to help strengthen the union between knowledge representation and computational linguistics in Bulgaria and CEE by means of a small-scale international programme of graduate education in knowledge representation and computational linguistics. The programme will take on four doctoral students, with at least three students from CEE (and at least one of these from Bulgaria). All doctoral students will be based throughout at the SfS and the LML. All doctoral students will have thesis proposals that agree with the aims of the programme. All doctoral students will be expected to complete their doctoral theses within the 24 month funding period, and to present the results of their work at seminars during the second CLARK summer school. In order to widen the impact of the programme in Bulgaria, the programme will also take on four master's students from Bulgaria. All master's students will be based throughout at the LML. All master's students will write theses on programme-related topics under the supervision of programme members, and in return for modest financial support will help with various tasks on the programme.

Teaching (top) (next) (prev)

In order to distribute the course materials and research findings of the programme, and to advertise the programme to the next generation of graduate students, we will organise two CLARK summer schools on the representation, acquisition and use of linguistic knowledge. The first summer school will be held in Bulgaria, in September 1999, and the second summer school will be held in Germany, in September 2000. Each summer school will last two weeks, and have an intake of up to 25 students with appropriate backgrounds in computer science, linguistics, mathematics and/or philosophy. For each summer school, the programme will provide grants for 6 students from Bulgaria and 6 students from CEE, as well as some discretionary support that the programme can flexibly allocate, for example, to assist students with exceptionally high travel costs. The courses will be given by the programme personnel, invited lecturers from the summer school host, and one or two invited external lecturers where appropriate. There will be lecture notes or recommended text books for the courses given by programme personnel. The language of instruction will be English. Examples of suitable seminars for the summer schools include
Mathematical Logic: Mathematical logic underlies both feature logics and knowledge representation languages. The course will present the intuitions and techniques of mathematical logic so that students will be able to recognise and exploit mathematical logic in linguistics and knowledge representation. The course materials will be based on existing materials, supplemented and updated as necessary.

Knowledge Representation: The course will present an overview of the basic notions of knowledge representation and reasoning. The materials will be example-based in order to give an intuitive understanding of the problems in the area. The course materials will be developed in the programme.

SRL and HPSG: The course will forge the linguistic half of our chosen link between linguistics and knowledge representation. In addition to the mathematical properties of SRL, the course will address the application of SRL to HPSG, focusing particularly on SRL formulations of such notions as linguistic truth and linguistic knowledge. The course material will be based on [King in prep.].

Declarative Knowledge Representation Languages: The course will complement the previous course, and forge the knowledge representation half of our chosen link between linguistics and knowledge representation. The course will present the syntax and semantics of a number of knowledge representation languages based on similar ontological assumptions: objects, sets of objects, and relations over objects. The course will include Kl-One-based languages, Conceptual Graphs, KIF and KQML. The course will also cover general topics such as structures of knowledge bases, functional interfaces to knowledge bases, inference techniques, the open- and closed-world assumptions, and knowledge translations. The course materials will be based on translations of existing Bulgarian materials, and will be further developed in the programme.

Knowledge Management: The course will be based on our existing and ongoing research on knowledge management. The course will include topics such as creating classificatory systems from finite SRL theories, tailoring classificatory systems, indexing over the classes in a classificatory system, reclassification and abduction. The course materials will be developed in the programme.

Implementation of HPSG Grammar Fragments in ConTroll: This course will offer practical hands-on experience to linguists and computer scientists interested in the formalisation of linguistic knowledge in the ConTroll system. The course will be taught in an interactive fashion in a computer laboratory and will combine background lectures with practical exercises on how to specify grammars in ConTroll. Students will be given the opportunity to undertake individualised grammar projects for modelling theoretically and empirically significant syntactic constructions of their native language. The background lectures will introduce the relevant mathematical and computational aspects of the ConTroll system and will focus on the main ingredients of constraint grammars: highly structured lexical representations, constituent structure, and encoding well-formedness constraints on grammatical representations. The course materials will be based on existing on-line teaching materials that have been developed by Hinrichs and Meurers for a course taught at the invitation of the program committee for the 9th Annual European Summer School in Logic, Language and Information, Aix-en-Provence, France, 1997.

Computational Morphology: The course will cover the basic notions in morphology - such as paradigm, lexeme, wordform, affixation and word - as well as problems with the automatic processing of the morphology of a natural language. The main formal approaches, such as two-level morphology, will be presented. Practical problems, such as the construction of a large morphological dictionary, will also be covered. The course materials will be developed in the programme.

In order to advertise the CLARK programme outside of the host institutions, we will also submit the best courses from our summer schools to larger international schools, such as the European Summer School in Logic, Language and Information.

References (top) (prev)

[Aldag 1997] Bjørn Aldag. A proof theoretic investigation of prediction in HPSG. Master's thesis. Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1997.

[Alt 1996] Natali I. Alt. A typed feature logic with set-valued attributes as a foundation for LP rules. Master's thesis. Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1996.

[Backofen, Trost and Uszkoreit 1991] Rolf Backofen, Harald Trost and Hans Uszkoreit. Linking typed feature formalisms and terminological knowledge representation languages in natural language front-ends. DFKI research report RR-91-28. DFKI, Saarbrücken, Germany. 1991.

[Carpenter 1992] Bob Carpenter. The Logic of Typed Feature Structures. Cambridge Tracts in Theoretical Computer Science, number 32. Cambridge University Press, Cambridge, England. 1992.

[Courbet et al. 1997] Elisabeth Courbet, Kordula De Kuthy, Detmar Meurers, Frank Richter and Manfred Sailer. Ein HPSG-Fragment des Deutschen, Teil 2: Implementierung. Sonderforschungsbereich 340 technical report. Sonderforschungsbereich 340, Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1997. In German.

[Franconi 1994] Enrico Franconi. Description logics for natural language processing. In The Working Notes of the 1994 AAAI Fall Symposium on ``Knowledge Representation for Natural Language Processing in Implemented Systems''. New Orleans, USA. 1994.

[Gerdemann and King 1994] Dale Gerdemann and Paul J. King. The correct and efficient implementation of appropriateness specifications for typed feature structures. In Proceedings of COLING'94, volume 2, pages 956-960. Kyoto, Japan. 1994.

[Götz and Meurers 1997a] Thilo Götz and W. Detmar Meurers. Interleaving universal principles and relational constraints over typed feature logic. In Proceedings of the 35th Meeting of the ACL and 8th Conference of the EACL. Madrid, Spain. 1997.

[Götz and Meurers 1997b] Thilo Götz and W. Detmar Meurers. The ConTroll system as large grammar development platform. In Proceedings of the ACL/EACL post-conference workshop on Computational Environments for Grammar Development and Linguistic Engineering. Madrid, Spain. 1997.

[Hinrichs, Kathol and Nakazawa 1997] Erhard W. Hinrichs, Andreas Kathol and Tsuneko Nakazawa (editors). Complex Predicates in Non-derivational Syntax. Syntax and Semantics Series. Academic Press, San Diego, California, USA. In press.

[Hinrichs and Nakazawa 1989] Erhard W. Hinrichs and Tsuneko Nakazawa. Flipped out: Aux in German. In Proceedings of the 25th Regional Meeting of the Chicago Linguistic Society. Chicago, Illinois, USA. 1989.

[Hinrichs and Nakazawa 1994] Erhard W. Hinrichs and Tsuneko Nakazawa. Linearizing finite Aux in German complex VPs. In John Nerbonne, Klaus Netter and Carl Pollard (editors), German in Head-Driven Phrase Structure Grammar. CSLI Lecture Notes, number 46. CSLI, Stanford, California, USA. 1994.

[Hinrichs and Nakazawa 1996] Erhard W. Hinrichs and Tsuneko Nakazawa. Applying lexical rules under subsumption. In Proceedings of COLING'96. Copenhagen, Denmark. 1996.

[Hinrichs and Nakazawa 1997a] Erhard W. Hinrichs and Tsuneko Nakazawa. PVP and split-NP topicalization in German. In Georgia Green und Beth Levine (editors), Studies in Head-Driven Phrase Structure Grammar. Cambridge University Press, Cambridge, England. In press.

[Hinrichs and Nakazawa 1997b] Erhard W. Hinrichs and Tsuneko Nakazawa. Third construction and VP extraposition in German. In [Hinrichs, Kathol and Nakazawa 1997].

[Hinrichs and Nakazawa in prep.] Erhard W. Hinrichs and Tsuneko Nakazawa. VP relatives in German. Paper presented at the International Conference on Head-Driven Phrase Structure Grammar. In Andreas Kathol, Jean-Pierre Koenig and Gert Webelhuth (editors), Studies in Constraint-Based Lexicalism. CSLI, Stanford, California, USA. In preparation.

[Hinrichs et al. 1994] Erhard W. Hinrichs, Dale Gerdemann, Paul J. King, Guido Minnen, and Thilo Götz. Ergebnisbericht des Teilprojekt B4 ``Constraints on Grammar for Efficient Generation''. In Sonderforschungsbereich 340 ``Sprachtheoretische Grundlagen für die Computerlinguistik'': Arbeits- und Ergebnisbericht 1992-1993-1994, pages 145-187. Sonderforschungsbereich 340, Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1994.

[Hinrichs et al. 1997] Erhard W. Hinrichs, Frank Richter, Detmar Meurers, Manfred Sailer and Heike Winhart. Ein HPSG-Fragment des Deutschen, Teil 1: Theorie. Sonderforschungsbereich 340 technical report 95. Sonderforschungsbereich 340, Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1997. In German.

[Johnson 1988] Mark Johnson. Attribute-Value Logic and the Theory of Grammar. CSLI Lecture Notes, number 16. CSLI, Stanford, California, USA. 1988.

[Kaplan and Bresnan 1982] Ronald M. Kaplan and Joan Bresnan. Lexical-functional grammar: A formal system for grammatical representation. In Joan Bresnan, editor, The Mental Representation of Grammatical Relations, chapter 4, pages 173-281. MIT Press, Cambridge, Massachusetts, USA, 1982.

[Kepser 1994] Stephan Kepser. A satisfiability algorithm for a typed feature logic. Master's thesis. Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1994.

[King 1989] Paul J. King. A Logical Formalism for Head-Driven Phrase Structure Grammar. Doctoral thesis. Department of Mathematics, University of Manchester, Manchester, England. 1989.

[King 1994a] Paul J. King. An expanded logical formalism for Head-driven Phrase Structure Grammar. Sonderforschungsbereich 340 technical report 59. Sonderforschungsbereich 340, Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1994.

[King 1994b] Paul J. King. Reconciling Austinian and Russellian accounts of the liar paradox. The Journal of Philosophical Logic, volume 23, number 5, pages 451-494. 1994.

[King 1994c] Paul J. King. Typed feature structures as descriptions. In Proceedings of COLING'94, volume 2, pages 1250-1254. Kyoto, Japan. 1994.

[King in prep.] Paul J. King. Truth and Verification in Head-driven Phrase Structure Grammar. In preparation.

[King and Simov 1998] Paul J. King and Kiril Iv. Simov. The automatic deduction of classificatory systems from linguistic theories. In Grammars, volume 1, number 2, 1998.

[King, Simov and Aldag 1998] Paul J. King, Kiril Iv. Simov and Bjørn Aldag. The complexity of modelability in finite and computable signatures of a constraint logic for head-driven phrase structure grammar. In The Journal of Logic, Language and Information. In press.

[Lager 1996] Torbjörn Lager A Logical Approach to Computational Corpus Linguistics. Doctoral thesis. Department of Linguistics, University of Göteborg, Göteborg, Sweden. 1996.

[Manandhar 1993] Suresh K. Manandhar. Relational Extensions to Feature Logic: Applications to Constraint Based Grammars. Doctoral thesis. Department of Artificial Intelligence, Faculty of Science and Engineering, University of Edinburgh, Edinburgh, Scotland. 1993.

[Meurers and Minnen 1997] W. Detmar Meurers and Guido Minnen. A computational treatment of lexical rules in HPSG as covariation in lexical entries. Computational Linguistics, volume 23, number 4. 1997.

[Nebel and Smolka 1991] Bernhard Nebel and Gert Smolka. Attributive description formalisms...and the rest of the world. DFKI research report RR-91-15. DFKI, Saarbrücken, Germany. 1991.

[Pollard 1998] Carl J. Pollard. Strong generative capacity in HPSG. In Gert Webelhuth, Jean-Pierre Koenig and Andreas Kathol (editors), Lexical and Constructional Aspects of Linguistic Explanation. CSLI, Stanford, California, USA. 1998.

[Pollard and Sag 1987] Carl J. Pollard and Ivan A. Sag. Information-Based Syntax and Semantics. CSLI Lecture Notes, number 13. CSLI, Stanford, California, USA. 1987.

[Pollard and Sag 1994] Carl J. Pollard and Ivan A. Sag. Head-Driven Phrase Structure Grammar. University of Chicago Press, Chicago, Illinois, USA. 1994.

[Popov, Simov and Vidinska 1997] Dimitar G. Popov, Kiril Iv. Simov and Svetlomira M. Vidinska. A Dictionary of Writing, Pronunciation and Punctuation of Bulgarian Language. Atlantis SD, Sofia, Bulgaria. In press. In Bulgarian.

[Popova 1994] Maria P. Popova. Kl-One knowledge representation language as query language to a relational database. Master's thesis. Faculty of Mathematics and Computer Science, St. Kliment Okhridski University, Sofia, Bulgaria. 1994. In Bulgarian.

[Quantz et al. 1995] J. Joachim Quantz, Guido Dunker, Manfred Gehrke, Uwe Küssner and Birte Schmitz. FLEX-based disambiguation in VERBMOBIL. In Alex Borgida, Maurizio Lenzerini, Daniele Nardi and Bernhard Nebel (editors), Proceedings of International Workshop on Description Logics. Dipartimento di Informatica e Sistematica, Universitá di Roma ``La Sapienza'', Rome, Italy. 1995.

[Richter and Sailer 1995] Frank Richter and Manfred Sailer. Remarks on linearization: reflections on the treatment of LP-rules in HPSG in a typed feature logic. Master's thesis. Seminar für Sprachwissenschaft, Eberhard-Karls-Universität, Tübingen, Germany. 1995.

[Simov 1995a] Kiril Iv. Simov. Communication among knowledge bases. Technical report. Linguistic Modelling Laboratory, Bulgarian Academy of Sciences, Sofia, Bulgaria. 1995. In Bulgarian.

[Simov 1995b] Kiril Iv. Simov. Declarative knowledge representation languages: Kl-One family, speciate re-entrant logic, conceptual graphs - an overview. Technical report. Linguistic Modelling Laboratory, Bulgarian Academy of Sciences, Sofia, Bulgaria. 1995.

[Simov 1997] Kiril Iv. Simov. Control of inference in declarative knowledge bases. Technical report. Linguistic Modelling Laboratory, Bulgarian Academy of Sciences, Sofia, Bulgaria. 1997. In Bulgarian.

[Simov and Boynov 1994] Kiril Iv. Simov and Nevelin P. Boynov. Conceptual graphs: the structure of the knowledge base and sublanguages. In Proceedings of the 1st Workshop on Conceptual Structure. Melbourne, Australia. 1994.

[Simov and Popov 1996] Kiril Iv. Simov and Dimitar G. Popov. Creating a morphological dictionary of the Bulgarian Language. In Proceedings of COMPLEX'96 Conference. Budapest, Hungary. 1996.

[Simov et al. 1990] Kiril Simov, Galia Angelova and Elena Paskaleva. MORPHO-ASSISTANT: The proper treatment of morphological knowledge. In Proceedings of COLING'90, volume 3, pages 453-457. Helsinki, Finland. 1990.

[Simov et al. 1992] Kiril Simov, Elena Paskaleva, Mariana Damova and Milena Slavcheva. MORPHO-ASSISTANT - a knowledge based system for Bulgarian morphology. Demo description in Proceeding of Demo Descriptions of Third conference on Natural Language Application. Trento, Italy. 1992.


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