File Information
File: 05-lr/acl_arc_1_sum/cleansed_text/xml_by_section/intro/91/w91-0113_intro.xml
Size: 11,547 bytes
Last Modified: 2025-10-06 14:05:05
<?xml version="1.0" standalone="yes"?> <Paper uid="W91-0113"> <Title>COMPILING TRACE & UNIFICATION GRAMMAR FOR PARSING AND GENERATION</Title> <Section position="3" start_page="0" end_page="102" type="intro"> <SectionTitle> 2 FORMALISM </SectionTitle> <Paragraph position="0"> The design of Trace and Unification Grammar has been guided by the following goals:</Paragraph> <Paragraph position="2"> erality, coverage , reliability and development speed of a grammar are a direct function of its perspicuity, just as programming in Pascal is less errorprone than programming in assembler. In the optimal case, the grammar writer shoul d be freed of reflections on how to code things best for processing but should only be guided by linguistic criteria. These goals led for .example to the introduction of unrestricted disjunction into the TUG formalism. null * Compatibility to GB Theory. It was a major objective bf the LKP to base the grammar on well undo;stood and motivated grounds.</Paragraph> <Paragraph position="3"> As most of the newer linguistic descriptions on German ate in the framework of GB theory, TUG was designed to be somehow compatible with this theory though it was not our goal to &quot;hardwire&quot; every Gs principle.</Paragraph> <Paragraph position="4"> * Efficiency. :As the LKP is supposed to be the basis of products for interactive usage of natural langu~age, efficiency is a very important goal. Making efficiency a design goal of the formalism led e.g. to the introduction of feature types 'and the separation of the movement rules int~ head movement and argument movement.</Paragraph> <Paragraph position="5"> The basis of TUG is formed by a context free grammar that is augmented by PATR n-style feature equations. Besides this basis, the main features of TUG are feature typing, mixing of attribute-value-pair and (PROLOG-) term unification, flexible macros, unrestricted disjunction and special rule types !for argument and head movement. null</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 2.1 BASIC FEATURES </SectionTitle> <Paragraph position="0"> As a very simple example we will look at the TUG version of the example grammar in Shieber (1984).</Paragraph> <Paragraph position="1"> ~type definition</Paragraph> <Paragraph position="3"> The two main differences to PATR II in the basic framwork are that first, TUG is leas flexible in that it has a &quot;hard&quot; contextfree backbone, whereas in PATR II categories of the context free part are placeholders for feature structures, their names boeing taken as the value of the cat feature in the structure. Second, TUG has a strict typing.</Paragraph> <Paragraph position="4"> For a feature path to be well defined, each of its attributes has to be declared in the type definition.</Paragraph> <Paragraph position="5"> Besides defined attribute-value-pairs, TUO allows for the mixing of attribute-value-pair unification with arbitrary structures like PROLOG terms using a back-quote notation. This can be regarded as the unificational variant of the BUILDQ operation known from ATNS. As an example consider the following lexicon entry of each that constructs a predicate logic notation out of dot :base, det:scope and det:var.</Paragraph> <Paragraph position="7"> During our work on the German grammar we found that this feature was very useful for the construction of semantic forms.</Paragraph> <Paragraph position="8"> TUG provides templates for a clearer organization of the grammar. The agreement in the above mentioned grammar might have been formulated like this:</Paragraph> <Paragraph position="10"> agree(np,vp).</Paragraph> <Paragraph position="11"> TUG allows for arbitrary disjunction of feature equations. Disjunctions and Conjunction may be mixed freely. Besides well known cases as in the entry for knight above, we found many cases where disjunctions of path equations are useful, e.g. for the description of the extraposed relative clauses*.</Paragraph> </Section> <Section position="2" start_page="0" end_page="102" type="sub_section"> <SectionTitle> 2.2 MOVEMENT RULES </SectionTitle> <Paragraph position="0"> Further to these more standard uG-features, TUG provides special rule formats for the description of discontinuous dependencies, so called &quot;movement rules&quot;. Two main types of movement are distinguished: argument movement and head movement. The format and processing of argument movement rules is greatly inspired by Chen e.a. (1988) and Chen (1990), the processing of head movement is based on GPSG like slash features. null Head Movement A head movement rule defines a relation between two positions in a parse tree, one is the landing site, the other the trace position. Head movement is constrained by the condition that the trace is the head of a specified sister (the root node) of 1Block/Sclunid (1991) describes our processing technique for disjunctions.</Paragraph> <Paragraph position="1"> the landing site 2. Trace and Antecedent are identical with the exception that the landing site contains overt material, the trace does'nt. Suppose, that v is the head of vk, vk the head of vp and vp the head of s, then only the first of the following structures is a correct head movement, the second is excluded because np is not head of vp, the third because antecedent and trace are unequal.</Paragraph> <Paragraph position="2"> Is, v~ Is ... \[vp ...</Paragraph> <Paragraph position="3"> \[vk ... trace(v), ...\]...\]...\]...\] Is' npt \[s ... \[vp trace(nph ...</Paragraph> <Paragraph position="4"> \[vk &quot;&quot; v ...\]...\],..\] Is, np~ \[s ... \[vp ...</Paragraph> <Paragraph position="5"> \[vk &quot;&quot; trace(vh ...\]...\].,.\]...\] To formulate head movement in TUG the following format is used. First, a head definition defines which category is the head of which other.</Paragraph> <Paragraph position="6"> v is_head_of vk.</Paragraph> <Paragraph position="7"> vk is_head_of vp.</Paragraph> <Paragraph position="8"> vp is_head_of s.</Paragraph> <Paragraph position="9"> Second, the landing site is defined by a rule like S j ---> V+S \] .,.</Paragraph> <Paragraph position="10"> To include recursive rules in the head path, heads are defined by the following head definitions. In a structure \[M D, ... D,\] D~ is the head of14 if either Di is_head_of 14 is defined or D~ has the same category as 14 and either Di is_head_of X or X is_head_of Dt is defined for any category X. Head movement rules are very well suited for a concise description of the positions of the finite verb in German (sentence initial, second and final) as in Hat~ der Mann der Frau das Buch gegeben t~ ? Hast the man the woman the book given tt Der Mann hat~ der Frau das Buch gegeben The man hast the woman the book given ti ... daft der Mann der Frau das Buch gegeben hat ... that the man the woman the book given has All that is needed are the head definitions and the rule that introduces the landing site 3.</Paragraph> <Paragraph position="11"> ~Here, &quot;head of&quot; is a transitive relation s.t. if x is head of y and y is head of z then x is head of z.</Paragraph> <Paragraph position="12"> SEven though verb movement is not supposed to be a topic for English grammar, one might think of describing English Subj-Aux inversion in terms of head movement. Peter hao been reading a book Has~ Peter ti been reading a book</Paragraph> <Paragraph position="14"/> </Section> <Section position="3" start_page="102" end_page="102" type="sub_section"> <SectionTitle> Argument Movement </SectionTitle> <Paragraph position="0"> Argument movement rules describe a relation between a landing site and a trace. The trace is always c-commanded by the landing site, its antecedent. Two different traces are distinguished, anaphoric traces and variable traces. Anaphoric traces must find their antecedent within the same bounding node, variable trace binding is constrained by subjacency, e.a. the binding of the trace to its antecedent must not cross two bounding nodes.' Anaphoric traces are found for example in English passive constructions Is \[np The book' of this author\]/ was read ti\] whereas variable graces are usually found in wh-constructions and~ topicalization. Similar to the proposal in Chen e.a. (1988), argument movement is coded in TUG by a rule that describes the landing site, as for example in</Paragraph> <Paragraph position="2"> This rule states that np: ante 4 is the antecedent of an np-trace that is dominated by sl. This rule describes a leftward movement. Following Chen's proposal, TUG also provides for rightward move- null ment rules, though these are not needed in the German grammar. A rightward movement rule might look like this.</Paragraph> <Paragraph position="3"> s2 ---> sl, traCe(var,np:trace)>np:an~e \[ ante:fx = trace:fx, The first argument in the trace-term indicates whether the landing site is for a variable (vat) or for an anaphoric (ana) trace. Other than head movement, where trace and antecedent are by definition identical, the feature sharing of argument traces with their 'antecedents has to be defined in the grammar by feature equations (ante:fx = trace: fx .... ). ~,Furthermore, it is not necessary that the antecedent and the trace have the same syntactic category. A rule for pronoun fronting in German might e.g. look like this: spr ---> pron<trace(ana0np), s \[ ...</Paragraph> <Paragraph position="4"> 4The notation Cat :Index is used to distinguish two or more occurrences of the same category in the same rule in the equation part. :ante and :trace are arbitrary names used as index to refer to the two different nps. The current version of the formalisms requires that the grammar contains a declaration on which categories are possible traces. In such a declaration it is possible to assign features to a trace, for example marking it as empty: erace(np) I np:e~pty = yes.</Paragraph> <Paragraph position="5"> Bounding nodes have to be declared as such in the grammar by statements of the form bounding_node(np).</Paragraph> <Paragraph position="6"> bounding_node(s) \[ s:tense = yes.</Paragraph> <Paragraph position="7"> As in the second case, bounding nodes may be defined in terms of category symbols and features 5. Typical long distance movement phenomena are described within this formalism as in GB by trace hopping. Below is a grammar fragment to describe the sentence Which books~ do you think ti John knows ti Mary did'nt understand ti: bounding_node(s).</Paragraph> <Paragraph position="8"> bounding_node(rip).</Paragraph> <Paragraph position="9"> sl ---> np<trace(vax,np), s I s ---> np, vp \[ ...</Paragraph> <Paragraph position="10"> s ---> aux, np, vp \[ ...</Paragraph> <Paragraph position="11"> np ---> propernoun \[ ...</Paragraph> <Paragraph position="12"> np ---> det, n \[ vp ---> v, sl \[ ...</Paragraph> <Paragraph position="13"> vp ---> v, np \[ ...</Paragraph> <Paragraph position="14"> trace(rip).</Paragraph> <Paragraph position="15"> The main difference of argument movement to other approaches for the description of discontinuities like extraposition grammars (Pereira 1981) is that argument movement is not restricted to nested rule application. This makes the approach especially atractive for a scrambling analysis of the relative free word order in the German Mittel/eld as in Ihml hatj das Buchk keiner ti tk gegeben tj.</Paragraph> </Section> </Section> class="xml-element"></Paper>