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<?xml version="1.0" standalone="yes"?> <Paper uid="C92-1012"> <Title>Towards Developing Reusable NLP Dictionaries</Title> <Section position="4" start_page="0" end_page="0" type="metho"> <SectionTitle> 3 The TFS Formalism </SectionTitle> <Paragraph position="0"> Before discussing the proposed lexicon architecture we will introduce the computational framework in which it has been formalized and ilnplemented, the formalism of typed feature structures.</Paragraph> <Paragraph position="1"> Currently the family of unification-based formafis:rLq is an emerging standard as the implementation formalism of natural language processing systems. A variant called typed feature structures, discussed a.o. in \[Carpenter, 1990\], \[Emele and Zajac, 1990\] and \[Zajac, 1990\], ha.s been adopted in a number of European lexicon projects, including ACQUILEX, Euito'raA 7 and MULTILEX. In the course of our project, a TFS database, user interface and a constraint solver have been implemented.</Paragraph> <Paragraph position="2"> TFS is an excellent formalism for computational lexicons, as it enables a definition of types, or classes, of linguistic objects, arranged in a multiple inheritance hierarchy, where types are associated with an appropriatehess specification defining their features and the types of those features and with (possibly disjunctive and complex) constraints. The object-oriented character of the system allows for minimization of redundancy, whereas the type system maximizes integrity of data.</Paragraph> <Paragraph position="3"> Three TFS-based tools have been developed: * a tool for interactive definition ~, entry and modification of data (cf. section 3.1).</Paragraph> <Paragraph position="4"> * a TFS database which can be accessed from the user interface and the constraint solver.</Paragraph> <Paragraph position="5"> 3The TFS-editor can bc used to interactively define a type hierarchy, as such a hierarchy can be viewed itself a.u a typed feature structure, ef. \[Fnkker, 1992\].</Paragraph> <Paragraph position="6"> Acra~s DE COLING-92, N^N'rI!S, 23-28 Ao'\]r 1992 5 4 Pgoc. OF COLING-92. NAN'fES, AUC;. 23-28, 1992 * a TFS-compiler for data manipulation, e.g. selections and conversion.</Paragraph> <Paragraph position="7"> The TFS-compiler is similar to the systems described by \[Carpenter, 1990\], \[Emele and Zajac, 1990\], and \[I,'ranz, 1990\], and like these it constitutes a general-purpose constraint-based formalism which can be used for a wide variety of tasks, including parsing, translation and generation. Our prototype is implemented on top of Sicstus Prolog, and is used primarily for selection and conversion of data. It offers a number of tracing and debugging facilities to assist in the design of typehierarchies and during query-evaluation.</Paragraph> <Paragraph position="8"> These three tools can import and export data in a special-pnrpo~ text format, whictl is useful for interchange and further processing. The acquisition tools for the Van Dale dictionaries and Celex can also generate their output in this format.</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 3.1 User Interface </SectionTitle> <Paragraph position="0"> The hierarchical definition of the grammatical types in TFS corresponds closely to a &quot;decision tree&quot; which the lexicographer traverses while editing a lemma. A graph~ teal user interface has been developed by the computer science department of the State University of Utrecht (\[Fokker, 1992\]) which allows the user to narrow down the main type of the lenrma (s)he is editing to a specific subtype and to subsequently edit the associated feature structure. For example, a lemma is refined li'om ENTRY to VERB to DATIVE_VERB, then constraints for this type are retrieved and the features and their substructures can be edited recursively.</Paragraph> <Paragraph position="1"> Of course, only appropriate features are presented and can be edited, e.g. it is impossible to edit a feature arg3 of an intransitive verb. While editing tile value of a fewture the editor creates a subwindow already positioned at the minimal type of this feature. E.g. while editing a verb, the feature semantics will already be positioned at the type EVENT, as this is the minimal type of this feature for verbs.</Paragraph> <Paragraph position="2"> The editor includes a useful help facility which can be viewed as an on-line instruction manual: a hell) function exists for each choice point which describes a number of criteria and examples to help making the decision.</Paragraph> <Paragraph position="3"> It will now be clear how lexicographic work using the decision tree model relates to importation of lcxical data from existing sources, such ms MRDs. These can he converted to partially edited lexical entries, so that the lexicographer doesn't have to start at the 'root' level (e.g. the choice point El/TRY in tile example), but at an intermediate level (e.g. VERB). Further choices lea(\[ to more refined descriptions of the word. Like all errors, errors iu the source dictionary can be corrected by moving back to a higher-level choice point in the hierarct~y.</Paragraph> <Paragraph position="4"> Completed entries, and also arbitrary substructures, can be named and stored iu a database for future use as shared (sub)structures in other entries. Useful applications of this cross-reference mecbanism are iu morphology and for the implementation of synonymy (see 4.2). Compounds can be assigned a feature tree with features left_daughter and right_daughter, whose values are pointers in the database to their constitnting parts.</Paragraph> <Paragraph position="5"> Tile editor has been implemented in C using tile Microsoft Windows 3.0 graphical interface. Tile progranr is designed to he e~mily portable, e.g. to X windows. The underlying database can be shared via a LAN. As the other tools, the database allows for import and export of feature structures in tile interchange format.</Paragraph> <Paragraph position="6"> The editor is designed specitically for the TFS forraalism. However it can tie used for any specific type hierarci~y, as tile definition of the type hierarchy is simply defined in a separate text file which is read by the program during start np. IIence, it is potentially interestillg for tile devch)pment of many other (NLP) dictionaries.</Paragraph> <Paragraph position="7"> An interesting elaboration of the editor would he to add extra functionality for the lexicographer besides editing attd viewing feature structures, such &~ facilities to consult wtrious on-line dictionaries or text corpora.</Paragraph> </Section> </Section> <Section position="5" start_page="0" end_page="0" type="metho"> <SectionTitle> 4 Dictionary organization </SectionTitle> <Paragraph position="0"> llaving introduced the computational framework wc will proceed with tile diseussion of the organization of the dictionary 4. The emph~asis has been on two types of modularity: I. Modularity of dictionaries and thesaurus.</Paragraph> <Paragraph position="1"> The general approach is to define clearly a munher of ahstractiou levels (cf. section 4,1) in order to achieve ccLsy conncctability of the monolingua\[ dictionaries via bilingual dictionaries. By geueraliz~ lug bilingual translation to bilingual synonymy (or equivalence, cf. section 4.2) wc can even separate se~ mantic descriptions (&quot;concepts&quot;) from the elements in which they arc realized in languages. Wc will show how such concel)tual dictionaries can bc generated from bilingual (fictionarics (4.3).</Paragraph> <Paragraph position="2"> 2. Modularity of grammatical description (cf. section ~).</Paragraph> <Paragraph position="3"> With respect to the linguistic content of tile mono lingual dicLiouaries (i.e. the grammatical description) we will diseuss the use of typed feature structure constraints expressing relations bctwcen gramdeg matical descriptions in various linguistic theories.</Paragraph> <Paragraph position="4"> This allows fi)r a very llexihle relation between var ions grammatical descriptions.</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 4.1 Tim m(~nollngual dictionary </SectionTitle> <Paragraph position="0"> Word forms in a language, ~Ls found in text corpora, arc associated with canonical forms according to \[exicological conventions. In particular contexts they are associated with cxact\]y one of a tixed finite number of designations ~. In \[Zgusta, 1971\], two other &quot;compo neuts&quot; of meaning are distinguished besides designation, viz. connotation and range of application. Our (somewhat poor) working definition of synonymy is a relation hctween readings sharing designation only, both within a language and across languages (where it is traditionally called equivalence).</Paragraph> <Paragraph position="1"> ~Thi.s is a condensed summary of \[van dcr Eijk, 1992a\].</Paragraph> <Paragraph position="2"> 5 Note that we ad(q~t the approach of discrete readings, el. \[tca Itltckcn, 199(}\].</Paragraph> <Paragraph position="3"> AcrEs I)E COLING-92, NANqES, 23~28 Ao(rr 1997. 5 5 }'R~)C. OF COI.ING 92, NAN-rEs, AU(I. 23-28, 1992 The relation between word forms aml canonical forms is many-to-many: ortimgrapllic variants are mapped onto a single canonical form, and a single word form call be related to ~veral lexical entries via inflectional rule* s. The monolingual dictionary is a net of lexical entries, which are pairings of canonical word forms of a language and their designations, and in addition describe their grarnrnatical properties.</Paragraph> <Paragraph position="4"> As a result, a lexical entry dmuld minimally have the two features canonical~form and semantics. The former feature has the simple type STRIM6, the latter, the description of the designation, has a complex value, po&'fibly including ~nrantic features, but minimally containing an identifying feature v, as we want to make sure it will always be possihle to interconnect tile monolingnal dictionaries via bilingual dictionaries. Apart from these two features, there will he other features for the d~criplion of the grammatical properties of the word.</Paragraph> <Paragraph position="5"> The combination of canonicalJ'orm and grammatical description should allow for the complete and correct generation of all word forms and their a.,mociated feature strnctures. As our intended client applications have front ends for this purpose the database was not designed to be a full form dictionary; tiffs could change, depending on the needs of future client applications.</Paragraph> <Paragraph position="6"> The ~t of designations can be viewed as a thesaurus or &quot;knowledge base&quot;; the lexical entries are &quot;pointers&quot; from words into this knowledge base, and can be implemented as sudl in TFS.</Paragraph> <Paragraph position="7"> The relation between canonical word forms and designations is also many-to-many, due to synonymy (several word forms related to the same designation) and lexical ambigality (one word form related to several designations). In addition to this there will be alternations in the description because of alternative grammatical patterns. These alternations are implemented as TFS disjunctions. null</Paragraph> </Section> <Section position="2" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 4.2 The bilingual dictionary </SectionTitle> <Paragraph position="0"> Bilingual dictionaries can be viewed as a relation between words in two languages. The levels &quot;word form&quot;, &quot;lexical entry&quot; and &quot;reading&quot; correspond to various degrees of granularity in bilingual dictionaries. Ideally, the bilingnal dictionary relates lexical items between languages at the level of readings, though in practice most existing dictionaries refer to canonical forms or even to word forum in the target language. Furthermore, the source language side in bilingual dictionaries usually refers to readings different from the monolingually motivated ones, because they are tuned to tile target language: two readings are not distinguished if they translate to the same word, or an additional reading is created for an additional translation. An exception is the original concept of the bilingual Van Dale dictionaries, where the source language reading structure of the bilingual 6g.g. the Dutch word form bekcnd is associated with the adjective bekcnd (meaning well-known)and (by participle formation) to the verb bekennen (to conJess).</Paragraph> <Paragraph position="1"> r'I'he name of t, tored semantic substructures in the TI:S database serves this purpose.</Paragraph> <Paragraph position="2"> dictionaries is hased directly on the moaolingual reading structure (of, \[van Sterkenhurg ef at., 1982\]).</Paragraph> <Paragraph position="3"> An interesting approach to the hilingual dictionary would be to view it ~.s describing pairings of bilingual synonyms. Tile advantage of this would be that 1. the dictionary supl)orts preservation of meaning in translation.</Paragraph> <Paragraph position="4"> 2. formal properties of equivalence relations (e.g. tran null sitive closure) can be exploited to automatically expaml the dictionary.</Paragraph> <Paragraph position="5"> 3. coding efforts call be reduced: tile detinition of the designation can be shared between monolingual and bilingual synonyms.</Paragraph> <Paragraph position="6"> Tile main difference hetween traditional dictionaries and our approach is therefore that tile indirect translational description of hilmgual synonymy is replaced by a direct relation between lexical entries in the nmnolingual dictionaries to all independent &quot;knowledge hase&quot; of synonym clusters. This approach is conamon ill e.g. multi-lingual terminology (cf. \[Picht and 1)raskau, 1985\]), but less common in lexicology.</Paragraph> <Paragraph position="7"> We will show that the two representations can be translated into each other. Section 4.3 describes how a knowledge base is generated from monolingual and bilingual dictionaries. A bilingual dictionary can be generated automatically from a set of monolingual dictionaries and a klmwledge base by enumerating the pairs of lexical entries in two monolingual dictionaries pointing to the same synonym cluster.</Paragraph> </Section> <Section position="3" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 4.3 Gcneratlng Synonym Clusters </SectionTitle> <Paragraph position="0"> Existing machine-readable trilingual dictionaries s can be converted to a representation based on bilingual synonymy, by &quot;extracting&quot; the underlying concepts. The process consists of tile following steps: First, the dictionaries are parsed and transformed to a table synoaym of the relation between a reading Rz in a language LZ and a reading R2 in L=. Two versions of this program have been developed and tested: one for the Van Dale Dutch-Spanish dictionary and one for bilingual entries in the EUROTRA transfer rule format. A version for dictionaries in a standard interchange format would be a possible future extension.</Paragraph> <Paragraph position="1"> Second, reflexive, symmetric, and transitive closure is applied to the synonyM/4 relation s. For each reading the generated synonym cluster can be viewed. E.g. according to tile Van Dale Dutch-Spanish dictionary, reading 0.1 of Dutch eerbetoon (English Onark of) honour) has one synonymous reading in Dutch and three synonyms in Spanish.</Paragraph> <Paragraph position="2"> eerbetoon O. 1 : SActually, there is no restriction to it b=lingual dk'tionary: severe.l bi- or multilinguM dictionaries, and even monolingual diction;tries of synonyms, can be processed similarly, resulting in a mulldingual dictionary. This has been checked using several Eurotra transfer dictionaries.</Paragraph> <Paragraph position="3"> 9'I'hl8 program was first hnplentented in Prolog for the Ndict system (\[Bloksma et el., 1990\]) itnd modified for a Frotetra research group on &quot;ll.cversibie Transfer&quot;. A(:rlis i)1~ COLINC~ 92, NAN-IES, 23-28 ^o(rI 2992 5 6 Psoc. O1: COLING-92, NANq'ES, AUG, 23-28, 2992 $s: { ho~t.najo honoras tributo }.</Paragraph> <Paragraph position="4"> nl: ( eQrbetoon_0,1 .arbo~ija 0.1 }, The current implementation is not yet fully satisfying.</Paragraph> <Paragraph position="5"> l|ecauea: there is no reading distinction on the ,ql)rmish side in the Van Dale N-S (only the Dutch words in the example are marked with a reading nmnber, e.g. 0.1), some cltinters will get mixed up Is E.g. Spanish fresco as adjective means fresh and a~ noun fresco, though the program will currently not slake this distinction.</Paragraph> <Paragraph position="6"> :frssco_0.1 : os: {frauco limpio refresco }.</Paragraph> <Paragraph position="7"> nl: { fresco 0,1 grin 0.1 }.</Paragraph> <Paragraph position="8"> The program couhl of course be modified to ~Lse the grummatical information about the target word in tbc dictionary as reading distinguisher; the noun fresco would then never be confimed with the adjective. This is ullde~iral)le ill l)rincil)lc, bowcver, at; we do not WKllt syntactic criteria to guide readiug distinction, l&quot;or in stance, many adjectives in I~x)mance languages have he mol)honous uominal counterparts, with identical morphology and ~manties. We don't want to be forced a priori to distinguish separate readings for the~e two cases. Furthermore, well-known examples of category shift iu translation re.g. adverbs translating to verbs etc.) show it is impossible to attach a unique syntactic category to an equivalence class.</Paragraph> <Paragraph position="9"> These presentations of synonym clusters can be very helpful to interaetively improve transfer dictionaries: errors of this type can easily he detected by native speakers of the languages (who need not know the other language) and corrected by creating appropriate reading distinction in Spanish.</Paragraph> <Paragraph position="10"> We cbecked the quality of tbe synonym clusters gener.</Paragraph> <Paragraph position="11"> ated from from both Van Dale and a EUItO'rRA Spanish Dutch dictionary. The Eurotra dictionary, where both source and target language items are referred to at the reading level, was converted to over 2187 chtsters, 315 of whicb contained more than one Spanish reading. Native speakers agreed with more than 95% of these synonym sets gcuerated via the bilingual elomlre step. The interpretation of bilingual translation as synonymy is therefore correct in the vast majority of eases.</Paragraph> <Paragraph position="12"> llowever, exceptions exist, such as tbe translation of the Spanish reloj, which, even though a true (aud infre quest) l)utch synonym exists (viz. uurwerk (el. English limepiece)), more commolfiy trauslate~ to one of its hypouyn~ besiege (Eng watch) or klok (Eng clock).</Paragraph> <Paragraph position="13"> An interesting e\[ahoration of our approach would be to extend the k*mwledge base by ordering the synouym clusters themselves via hypono,ny It (cf. \[Cruse, 1986\], ldeg'l'he problem of c'annecting word forms to their readings ha* lu'en called the mappin 9 t~roblem. Gf. \[llyrd cl al., 1987\] for discussion of a method to map word forms to readings by comparing a.o. t~enlastic featnres like human of the source re~ling and potentiM target reaAings.</Paragraph> <Paragraph position="14"> l*'I'his idea is simil~tr to Wordnet, a collection of synonynl sets linked via a variety of Icxical relations (\[Bcckwirth et al., 1989\]). Our &pproadl extends this idea by adding a multilin gtlaJ dimension. Wordset's sylloltym t~tt~ are ~.lsO related by relations with leas oh:as translational contu:qu(mt:cn.</Paragraph> <Paragraph position="15"> \[Lyous, 1977\]). Client applications could then extract Irauslati(mal data based not only on synonymy but also on hyp(er)onymy. However. this is a dillicult area, where no obvious solutions exist. It is not clear at all which translatiou solution automatic translators should select in c~mes like this anyway.</Paragraph> <Paragraph position="16"> After thls correction process the synonyln clnsters can be couverted to TFS format and stored in the database, The a.~sociated monolingunl dictk)nnries are then modi fled automatically by adding cross-reference informatiott (via the feature se mastics) from the lcxicnl entries to the synonym dustcrs they use a~uociated with.</Paragraph> </Section> <Section position="4" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 4.4 Creating a knowledge I)ase. </SectionTitle> <Paragraph position="0"> Synonym clusters reMly become descriptions of designations once semautlc information is added to the syn onym dusters, which is then, in a truly interlingual way, shared between synonyms. Much mmlaxltic information froul the (~ELEX 1)utch dictionary can I>e moved to the synonym clusters, as well as Van Dale defiuitious of concepts in natural language. Tbc latter arc useful for semiautomntic interactive applications Is.</Paragraph> <Paragraph position="1"> The current approach can be said to inlpiement the apo proach of possible bilingual lexlcal translalioa, Tiffs al> preach should he developed in a uumber of ways. Apart from the problem of translation to non-synouyms we mentioned, it is desirable to inchLde information in the dictionary to guide the choice among possible translations, iu cases where there are several syuonyms in the target language. Stylistic, eolloeational and frequency infl)rmation can be of use for this purpose. This infer motion is partly available from existing sources (sucb as CF, I,EX attd Van Dale), and large text corpora are also obviously relevant sources of this information.</Paragraph> </Section> </Section> <Section position="6" start_page="0" end_page="0" type="metho"> <SectionTitle> 5 A model for conversion </SectionTitle> <Paragraph position="0"> Conversion or exchange of lexical data presupposes a detailed comparison of the various dictiouaries, which in turn requires a careful description of the various dictionaries. Given the purpose of Comparison, the descriptions shouM be cast in a uniform, preferably high-level data descriptiou lauguage. Several such languages exist, such as the Entity- Relationship model, a tool in database design. We will use the TFS formalism introduced in ~ction 3 for this purpose.</Paragraph> <Paragraph position="1"> A lirst step in tiffs comparison is to convcrt various dictionaries to the uniforln TFS format. In \[n~xqt NI,P formalisms lexical entries are records or feature structures, so this syntactic transformation is generally unproblematic. In passing, implicit semantic structure in the wtr. ious dictionaries (e.g. feature cooeeurrence r~trictions) can be re,Meted explicit hy constructing a type hierarchy for the~ uystcms, ()n the hasis of these descril)tions, constraints on the rehttion hetwc~m lexical entries in the dilt~rent dictio naries cau be detined, These constraints can be called Also see \[Calzolari, 1990\] for a i)roposM aimil~,r to ours to integrate the dictionary and the thesaurus.</Paragraph> <Paragraph position="2"> la l&quot;or exautple, l{o.uetta illcorl)tltate~..3.11 interactive rea(Ihtg selection \[acillty.</Paragraph> <Paragraph position="3"> Acrli~; l)t!('(J ING 92. NAN ~ ES. 2~28 ao(Tr 1!)92 5 7 PRec. o1: COl,IN(; 92. NANTES. AUG, 23 28. 1992 semantic, as they relate the content of the various dictionaries, and neutral as they merely pinpoint correspondences between dictionaries; they define the way dictionaries (which may be unrelated in other respects) are similar.</Paragraph> <Paragraph position="4"> Constraints can be viewed as implicational and biconditional constraints (as in \[van der Eijk, 1992b\]), and it is possible to implement them as a complex TFS type.</Paragraph> <Paragraph position="5"> This type serves both as documentation of the dictionary and as conversion specification.</Paragraph> <Paragraph position="6"> A conversion specification is a TFS type CONVERT having features for each of the dictionaries (e.g. lezic, eurotra and rosetta), and establishes the basic conversion relation between entries in the LEXIC dictionary (as derived from the sources and augmented by lexicographers) and entries in the EtrROTRA and ROSETTA dictionaries.</Paragraph> <Paragraph position="7"> This conversion type is structured hierarchically as well: the high-level type CONVERT has many subtypes specifying how specific subtypes (and hence subsets of the respective lexicons) of the various dictionaries are related. Disjuncts in the constraints of these types enumerate corresponding patterns described as feature structures.</Paragraph> <Paragraph position="8"> An advantage is that these conversion constraints can be defined at the appropriate level of abstraction. It is in principle possible to establish relations holding for all entries as well as for an individual entry. As the conversion types are also ordered in an inheritance hierarchy, sub-types will inherit the constraints of their supertype(s).</Paragraph> <Paragraph position="9"> Note the inherent declarative character of the conversion constraints: there is no notion of 'input' and 'output'. One advantage of this is that a single formalism can be nsed for importation, generation as well as integration of lexicons. A second advantage is that the conversion constraints can also be used to test whethcr two existing dictionaries are related as postulated in the conversion constraints.</Paragraph> <Paragraph position="10"> Full derivability of a particular dictionary can be viewed as a special case of the general (in principle relational) scheme, where the substructure of a feature like rosetta is fully (and functionally) derivable from the sub-structure of another (lezic). Informally, all primitive distinctions in the target dictionary can be computed given the information in the source dictionary, i.e. the constraints define a homomorphism from the serving dictionary to the client application.</Paragraph> <Paragraph position="11"> It is an empirical issue whether this derivability relation can actually he defined between two dictionaries.</Paragraph> <Paragraph position="12"> For newly to be created &quot;generic&quot; lexicons, this derivability is a design requirement. For the client dictionaries we have had to look at, creation of a generic source appeared to be a complex, but feasible, task.</Paragraph> <Paragraph position="13"> Operationally, conversion proceeds as query-evaluation. Givcn an appropriate dcfinition of the CONVERT type, the solutions to the following query will find all lexieal entries whose canonical form is tiers in the LExIc database and return all corresponding further instantiations of the ROSETrA type.</Paragraph> <Paragraph position="14"> These instantiations correspond to the I~.OSETTA descriptions for this lexical entry.</Paragraph> <Paragraph position="15"> Icdeg'&quot;'i ENTRY lexic : canonical_form :fiets rosetta : ROSETTA</Paragraph> </Section> <Section position="7" start_page="0" end_page="0" type="metho"> <SectionTitle> 6 Illustration </SectionTitle> <Paragraph position="0"> We will illustrate conversion using the example in \[van der Eijk, 1992a\] relating two familiar linguistic theories, GPSG and a unification variant of Categoria\] Grammar, rather than the LEXIC fragment and ROSETTA, which we actually implemented.</Paragraph> <Paragraph position="1"> The categorial lexical entries have a feature subcat whose value is either a CATEGORY or a FUNCTION. The type FUNCTION has appropriate features argument, (with two features direction and category), and result, where the result can be either a function again or a CATEGORY.</Paragraph> <Paragraph position="2"> Individual Icxical entries are simply instances of this highly general recursive scheme. E.g. the subcat feature of a transitive verb (i.e. (NP\S)/NP) has type FUNCTION, with an NP argument to the right and, recursively, a FUNCTION from a subject NP to an S as result.</Paragraph> <Paragraph position="3"> In GPSG individual lexical entries also have a feature subcat, but its value, an intcgcr, is used to select the corresponding context-free grammar rule for this complcmentation pattern.</Paragraph> <Paragraph position="4"> One of the disjuncts of the constrain ts for the CONVERT type will then be the following. Unifying specific categorial entries into the cg substructure will cause the curresponding gpsg feature to become instantiated.</Paragraph> </Section> <Section position="8" start_page="0" end_page="0" type="metho"> <SectionTitle> * CONVERT </SectionTitle> <Paragraph position="0"> cg : subcat :</Paragraph> </Section> class="xml-element"></Paper>