{ "paper_id": "P03-1024", "header": { "generated_with": "S2ORC 1.0.0", "date_generated": "2023-01-19T09:14:56.289760Z" }, "title": "Generating parallel multilingual LFG-TAG grammars from a MetaGrammar", "authors": [ { "first": "Lionel", "middle": [], "last": "Cl\u00e9ment", "suffix": "", "affiliation": { "laboratory": "", "institution": "Inria-Roquencourt", "location": { "country": "France" } }, "email": "lionel.clement@inria.fr" }, { "first": "Alexandra", "middle": [], "last": "Kinyon", "suffix": "", "affiliation": {}, "email": "kinyon@linc.cis.upenn.edu" } ], "year": "", "venue": null, "identifiers": {}, "abstract": "We introduce a MetaGrammar, which allows us to automatically generate, from a single and compact MetaGrammar hierarchy, parallel Lexical Functional Grammars (LFG) and Tree-Adjoining Grammars (TAG) for French and for English: the grammar writer specifies in compact manner syntactic properties that are potentially framework-, and to some extent language-independent (such as subcategorization, valency alternations and realization of syntactic functions), from which grammars for several frameworks and languages are automatically generated offline. 1", "pdf_parse": { "paper_id": "P03-1024", "_pdf_hash": "", "abstract": [ { "text": "We introduce a MetaGrammar, which allows us to automatically generate, from a single and compact MetaGrammar hierarchy, parallel Lexical Functional Grammars (LFG) and Tree-Adjoining Grammars (TAG) for French and for English: the grammar writer specifies in compact manner syntactic properties that are potentially framework-, and to some extent language-independent (such as subcategorization, valency alternations and realization of syntactic functions), from which grammars for several frameworks and languages are automatically generated offline. 1", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Abstract", "sec_num": null } ], "body_text": [ { "text": "Expensive dedicated tools and resources (e.g. grammars, parsers, lexicons, etc.) have been developed for a variety of grammar formalisms, which all have the same goal: model the syntactic properties of natural language, but resort to a different machinery to achieve that goal. However, there are some core syntactic phenomena on which a cross-framework (and to some extent a cross-language) consensus exists, such as the notions of subcategorization, valency alternations, syntactic function. From a theoretical perspective, a MetaGrammatical level of representation allows one to encode such consensual pieces of syntactic knowledge and to compare different frameworks and languages. From a practical perspective, encoding syntactic phenomena at a metagrammatical level, from which grammars for different frameworks and languages are generated offline, has several advantages such as portability among grammatical frameworks, better parallelism, increased coherence and consistency in the grammars generated and less need for human intervention in the grammar development process.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Introduction", "sec_num": "1" }, { "text": "In section 2, we explain the notion of MetaGrammar (MG), present the MG tool we use to generate TAGs, and how we extend the approach to generate LFGs. In section 3, we justify the use of a MetaGrammar for generating LFGs and explore several options, i.e. domains of locality, for doing so. In sections 4 and 5, we discus the handling of valency alternations without resorting to LFG lexical rules, and the treatment of long-distance dependencies. In sections 6 and 7, we discuss the advantages of a MG approach and the automatic generation of parallel TAG-LFG grammars for English and for French with an explicit sharing of both cross-language and cross-framework syntactic knowledge in the MG.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Introduction", "sec_num": "1" }, { "text": "The notion of MetaGrammar was originally presented in (Candito, 1996) to automatically generate wide-coverage TAGs for French and Italian 2 , using a compact higher-level layer of linguistic description which imposes a general organization for syntactic information in a three-dimensional hierarchy:", "cite_spans": [ { "start": 54, "end": 69, "text": "(Candito, 1996)", "ref_id": "BIBREF6" } ], "ref_spans": [], "eq_spans": [], "section": "What is a MetaGrammar ?", "sec_num": "2" }, { "text": "\u2022 Dimension 1: initial subcategorization \u2022 Dimension 2: valency alternations and redistribution of functions \u2022 Dimension 3: surface realization of arguments. Each terminal class in dimension 1 encodes an initial subcategorization (i.e. transitive, ditransitive etc...); Each terminal class in dimension 2 -a list of ordered redistributions of functions (e.g. to add an argument for causatives, to erase one for passive with no agents ...); Each terminal class in dimension 3 -the surface realization of a syntactic function (e.g. declares if a direct-object is pronominalized, wh-extracted, etc.). Each class in the hierarchy is associated to the partial description of a tree (Rogers and Vijay-Shanker, 1994) which encodes father, dominance, equality and precedence relations between nodes. A well-formed tree is generated by inheriting from exactly one terminal class from dimension 1, one terminal class from dimension 2 3 , and n terminal classes from dimension 3 (where n is the number of arguments of the elementary tree being generated). For instance, the elementary tree for \"Par qui sera accompagn\u00e9e Marie\" (By whom will Mary be accompanied) is generated by inheriting from transitive in dimension 1, from passive in dimension 2 and subject-nominal-inverted for its subject and Wh-questioned-object for its object in dimension 3. This particular tool was used to develop from a compact hand-coded hierarchy of a few dozen nodes, a wide-coverage TAG for French of 5000 elementary trees (Abeill\u00e9 et al., 1999) , as well as a medium-size TAG for Italian (Candito, 1999) . The compactness of the hierarchy is due to the fact that nodes are defined only for simple syntactic phenomena: classes for complex syntactic phenomena (e.g. Topicalized-object+Pronominalized) are generated by automatic crossings of classes for simple phenomena. In addition to proposing a compact representation of syntactic knowledge, (Candito, 1999) explored whether some components of the hierarchy could be re-used across similar languages (French and Italian). However, she developed two distinct hierarchies to generate grammars for these two languages and generated only TAG grammars. We extend the use of the MetaGrammar to generate LFGs and also push further its cross-language and cross-framework potential by generating parallel TAGs and LFGs for English and French from one single hierarchy 4 .", "cite_spans": [ { "start": 1494, "end": 1516, "text": "(Abeill\u00e9 et al., 1999)", "ref_id": "BIBREF0" }, { "start": 1560, "end": 1575, "text": "(Candito, 1999)", "ref_id": "BIBREF7" }, { "start": 1915, "end": 1930, "text": "(Candito, 1999)", "ref_id": "BIBREF7" } ], "ref_spans": [], "eq_spans": [], "section": "What is a MetaGrammar ?", "sec_num": "2" }, { "text": "The grammar rules we generate are sorted by syntactic phenomena, thanks to the notion of HyperTag, introduced in (Kinyon, 2000). The main idea behind HyperTags is to keep track, when trees (i.e. grammar rules) are generated from a MetaGrammar hierarchy, of which terminal classes were used for generating the tree. This allows one to obtain a frameworkindependent feature structure containing the salient syntactic characteristics of each grammar rule 5 . For instance, the verb give in A book was given to Mary could be assigned the HyperTag: Although we retain the linguistic insights presented in (Candito, 1996) , that is the three dimensions to model syntax, (subcategorization, valency alternation, realization of syntactic arguments), we slightly alter it, and add sub-dimensions for the realization of predicates as well as modifiers. Moreover, we use a different MetaGrammar tool which is less framework-dependent and supports the notion of Hy-perTag.", "cite_spans": [ { "start": 600, "end": 615, "text": "(Candito, 1996)", "ref_id": "BIBREF6" } ], "ref_spans": [], "eq_spans": [], "section": "HyperTags", "sec_num": "2.1" }, { "text": "\uf8ee \uf8ef \uf8ef \uf8ef \uf8ef \uf8ef \uf8f0 Subcat", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "HyperTags", "sec_num": "2.1" }, { "text": "To generate TAGs and LFGs, we use the MG compiler presented in (Gaiffe et al., 2002) 6 . Each class in the MG hierarchy encodes:", "cite_spans": [ { "start": 63, "end": 86, "text": "(Gaiffe et al., 2002) 6", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "The LORIA MetaGrammar tool", "sec_num": "2.2" }, { "text": "\u2022 Its SuperClasse(s) \u2022 A HyperTag which captures the salient linguistic characteristics of that class.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "The LORIA MetaGrammar tool", "sec_num": "2.2" }, { "text": "\u2022 What the class needs and provides.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "The LORIA MetaGrammar tool", "sec_num": "2.2" }, { "text": "\u2022 A set of quasi-nodes (i.e. variables)", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "The LORIA MetaGrammar tool", "sec_num": "2.2" }, { "text": "\u2022 Topological relations between these nodes (father, dominates, precedes, equals) 7 \u2022 A function for each quasi-nodes to decorate the tree (e.g. traditional agreement features and/or LFG functional equations). The MG tool automatically crosses the nodes in the hierarchy, looking to create \"balanced\" classes, that is classes that do not need nor provide any resource 8 . Then for each balanced terminal class, the HyperTags are unified, and the structural constraints between quasi-nodes are unified; If the unification succeeds, one or more pairs are generated. When generating a TAG, tree is interpreted as a TAG elementary tree (i.e. a grammar rule). When generating an LFG, tree is a tree decorated with traditional LFG functional annotations (in a way which is similar to constituent trees decorated with functional annotation e.g. by (Frank, 2000) ), and is in a second step broken down into one or more LFG rules. Figure 1 illustrates how a simple decorated tree is generated with the MG compiler, and how the decorated tree corresponds to one TAG elementary tree and to two LFG rewriting rules for a canonical transitive construction. In addition, to facilitate the grammar-lexicon interface, each decorated tree yields an LFG lexical template (here, Sub-jObj:V (\u2191Pred='x<(\u2191Subj)(\u2191Obj)>').", "cite_spans": [ { "start": 858, "end": 871, "text": "(Frank, 2000)", "ref_id": "BIBREF13" } ], "ref_spans": [ { "start": 939, "end": 947, "text": "Figure 1", "ref_id": null } ], "eq_spans": [], "section": "The LORIA MetaGrammar tool", "sec_num": "2.2" }, { "text": "Because TAGs are a tree rewriting system, there are intrinsic redundancies in the rules of a TAG. E.g., all the rules for verbs with a canonical NP subject and a canonical realization of the verb will have a redundant piece of structure (S NP0\u2193 (VP (V\u22c4))) . This piece of structure will be present not only for each new subcategorization frame (intransitive, transitive, ditransitive...), but also for all related non-canonical syntactic constructions such as in each grammar rule encoding a Wh-extracted object. This redundancy justifies the use of a MetaGrammar for TAGs. Since LFG rules rely on a context free backbone, it is generally admitted that there is less redundancy in LFG than in TAG. However, there are still redundancies, at the level of rewriting rules, at the level of functional equations, and at the level of lexical entries. To illustrate such redundancies, we take the example of French ditransitives with the insertion of one or more modifiers. The direct object is realized as an NP, the second object as a PP. Both orders NP PP and PP NP are acceptable. On top of that, one or more modifiers may be inserted before, after or between the two arguments, and can be of almost any category (PP, ADVP, Figure 1 : A simple hierarchy which yields one decorated tree, corresponding to one TAG rule and two LFG rules ( \u2192 stands for father, < for precedes in the MG hierarchy. \u22c4 \u2193 resp. stand for \"anchor\" and substitution nodes in TAGs. \u2193 and \u2191 stand for standard LFGs functional equations. NP etc.). Here is a non exhaustive list of acceptable word-order variations:", "cite_spans": [], "ref_spans": [ { "start": 1221, "end": 1229, "text": "Figure 1", "ref_id": null } ], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "-Jean donne une pomme\u00e0 Marie (lit: J. gives an apple to M.) -Jean donne\u00e0 Marie une pomme (lit: J. gives to M. an apple) -Jean aujourd'hui donne\u00e0 Marie une pomme (lit: J. today gives to M. an apple) -Jean donne\u00e0 Marie chaque matin une pomme avant le d\u00e9part du train (lit: J gives to M. every morning an apple before the departure of the train) -Jean donne chaque matin\u00e0 Marie une pomme (lit: J. gives each morning to M. an apple) -Aujourd'hui Jean donne\u00e0 Marie une pomme (lit: Today J. gives to M. an apple)", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "A first rule for VP expansion, accounting for the free order between the first and second object without modifiers, is shown below:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "VP \u2192 V (NP) PP (NP) \u2191=\u2193 (\u2191Obj)=\u2193 (\u2191SecondObj)=\u2193 (\u2191Obj)=\u2193", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "This VP rule is redundant: the NP is mentioned twice, with its associated functional equation. The NPs are both marked optional because at least one of them has to be not realized, else no well-formed Fstructure could be built since the uniqueness condition would be violated by the presence of two directobjects: for a sentence such as \"*Jean donne une pomme\u00e0 Mary une pomme\"/J. gives an apple to M. an apple, a C-structure would be built but, as expected, no corresponding well-formed F-structure. Let us now enrich the rule to account for modifier insertion. This yields the VP expansion shown in 2(a).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "The rule for VP expansion is now highly redundant, although the syntactic phenomena handled by this rule are very simple ones: the NP for the direct object is repeated twice, along with its functional equation, the disjunction (ADVP|NP|PP) is repeated 5 times, again with its functional equation. This gives us grounds to support a MetaGrammar type of organization for LFG. In practice, as described in (Kaplan and Maxwell, 1996) , additional LFG notation is available such as operators like \"insert or ignore\", \"shuffle\" \"ID/LP\", \"Macros\" etc. However, these operators, which are motivated from a formal perspective, but not so much from a linguistic perspective, yield two major problems: first, not all LFG parsers support those additional operators. Second, the proliferation of operators allows for a same rule to be expressed in many different ways, which is helpful for grammar writing purpose, but not so desirable for maintenance purpose 9 . Although nothing pre- Figure 2 : VP expansion vents the MG generator to create rules with operators such as \"ignore or insert\", we chose not to do so. Instead of generating rules with operators or rules like (2a), we generate two rules (2b) and (2c) in order to have uniqueness, completeness and coherence not only at the F-structure level but also at the C-structure level. 10 . Moreover, for lexical organization, practical LFGs resort to the notion of lexical template but from a linguistic perspective, the lexicon is not cleanly organized in LFG 11 .", "cite_spans": [ { "start": 403, "end": 429, "text": "(Kaplan and Maxwell, 1996)", "ref_id": null } ], "ref_spans": [ { "start": 973, "end": 981, "text": "Figure 2", "ref_id": null } ], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "(a) VP \u2192 (ADVP|NP|PP)* V (ADVP|NP|PP)* (NP) (ADVP|NP|PP)* PP (ADVP|NP|PP)* (NP) (ADVP|NP|PP)* (\u2191Modif) \u220b\u2193 \u2191=\u2193 (\u2191Modif)\u220b\u2193 (\u2191Obj)=\u2193 (\u2191Modif)\u220b\u2193 (\u2191SecObj)=\u2193(\u2191Modif)\u220b\u2193 (\u2191Obj)=\u2193 (\u2191Modif)\u220b\u2193 (b) VP \u2192 (ADVP|NP|PP)* V (ADVP|NP|PP)* NP (ADVP|NP|PP)* PP (ADVP|NP|PP)* (\u2191Modif) \u220b\u2193 \u2191=\u2193 (\u2191Modif)\u220b\u2193 (\u2191Obj)=\u2193 (\u2191Modif)\u220b\u2193 (\u2191SecObj)=\u2193(\u2191Modif)\u220b\u2193 (c) VP \u2192 (ADVP|NP|PP)* V (ADVP|NP|PP)* PP (ADVP|NP|PP)* NP (ADVP|NP|PP)* (\u2191Modif) \u220b\u2193 \u2191=\u2193 (\u2191Modif)\u220b\u2193 (\u2191SecObj)=\u2193(\u2191Modif)\u220b\u2193 (\u2191Obj)=\u2193 (\u2191Modif)\u220b\u2193", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Redundancies in LFG", "sec_num": "3.1" }, { "text": "We have seen in section 2.2 that the MG tool we use outputs pairs, where tree is decorated with functional equations and corresponds to one or more LFG rewriting rules (Figure 1) .", "cite_spans": [], "ref_spans": [ { "start": 185, "end": 195, "text": "(Figure 1)", "ref_id": null } ], "eq_spans": [], "section": "Exploring different domains of locality", "sec_num": "3.2" }, { "text": "VP V (\u2191Family)=SubjObjPrepObj \u2191Pred='x<(\u2191Subj)(\u2191Obj)(\u2191de-Obj)>' NP (\u2191Obj)=\u2193 PP (\u2191(\u2193pcase)Obj)=\u2193 VP \u2192 V PP N2 \u2191=\u2193 (\u2191(\u2193 pcase)Obj)=\u2193 (\u2191 object)=\u2193 SubjObjectPrepObject:V (\u2191 pred = 'x <(\u2191 Subj) (\u2191 Obj) (\u2191 de-Obj)>'", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Exploring different domains of locality", "sec_num": "3.2" }, { "text": "In order to generate LFG rules with a MG, we have two options. The first option consists in generating \"standard\" LFG rules, that is trees of depth 1 decorated with functional equations. Figure 3 illustrates detailed discussion of the (Kaplan and Maxwell, 1996) operators is found in (Cl\u00e9ment and Kinyon, 2003) .", "cite_spans": [ { "start": 235, "end": 261, "text": "(Kaplan and Maxwell, 1996)", "ref_id": null }, { "start": 284, "end": 310, "text": "(Cl\u00e9ment and Kinyon, 2003)", "ref_id": "BIBREF8" } ], "ref_spans": [ { "start": 187, "end": 195, "text": "Figure 3", "ref_id": null } ], "eq_spans": [], "section": "Figure 3: LFG Rule and a lexical entry", "sec_num": null }, { "text": "10 Thus the grammars we generate exhibit redundancies for modifiers, but, since the MG hierarchy has relatively few redundancies, and since these grammars are automatically generated, the problem is minor.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Figure 3: LFG Rule and a lexical entry", "sec_num": null }, { "text": "11 As opposed for instance to lexical organization not only in TAGs and TAG related framework (e.g. DATR (Evans et al., 2000) ), but in HPSG (Flickinger, 1987) . such as decorated tree, which yields one LFG rewriting rule, and one lexical entry for French verbs such as \"\u00e9loigner\" ( take away from), which take an NP object and a PP object introduced by \"de\". (Ex: \"Peter\u00e9loigne son enfant de la fen\u00eatre\"/ P. takes his child away from the window). The second option, which is the one we have opted for, consists in generating constituent trees which may be of depth superior to one, decorated with feature equations. It has the following advantages:", "cite_spans": [ { "start": 105, "end": 125, "text": "(Evans et al., 2000)", "ref_id": "BIBREF11" }, { "start": 141, "end": 159, "text": "(Flickinger, 1987)", "ref_id": "BIBREF12" } ], "ref_spans": [], "eq_spans": [], "section": "Figure 3: LFG Rule and a lexical entry", "sec_num": null }, { "text": "\u2022 It allows for a more natural parallelism between the TAG and LFG grammars generated \u2022 It allows for a more natural encoding of syntax at the MetaGrammar level \u2022 It allows us to generate LFGs without Lexical Rules \u2022 It allows us to easily handle long-distance dependencies.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Figure 3: LFG Rule and a lexical entry", "sec_num": null }, { "text": "The trees decorated with LFG functional annotations are then decomposed into standard LFG rewriting rules and lexical entries 12 . The grammar we obtain is then interfaced with a parser 13 . Concerning the first point (TAG-LFG parallelism), the trees decorated with functional equations and TAG elementary trees are very similar, as was first discussed in (Kameyama, 1986) . Concerning the second point (more natural encoding of the MetaGrammar level), the \"resource model\" of the MetaGrammar, based on \"needs\" and \"provides\", allows for a natural encoding and enforcement of LFG coherence, completeness and uniqueness principles: A transitive verb needs exactly one resource \"Subject\" and one resource \"Object\". Violations result in invalid classes which do not yield any rules. So from that perspective, it makes little sense, apart from practical reasons such as interfacing the grammar with an existing parser, to force the rules generated to be trees of depth one. Moreover, classical completeness/coherence conditions have received a similar resource-sensitive re-interpretation in LFG to compute semantic structures using linear logic (Dalrymple et al., 1995) . We devote the next two sections to the third (lexical rules) and fourth (wh) points. Traditional LFGs encode phrase structure realizations of syntactic functions such as the wh-extraction or pronominalization of an object in phrase structure rules. In the MetaGrammar, these are encoded in the \"Argument Realization\" dimension (dimension 3 in Candito's terminology). For valency alternations, i.e. when initial syntactic functions are modified, LFG resorts to the additional machinery of lexical rules 14 . However, these valency alternations are encoded directly in the MetaGrammar in the \"valency alternation\" dimension (dimension 2 in Candito's terminology). Hence, when a rule is generated for a canonical transitive verb, rules are generated not only for all possible argument realization for the subject and direct object (wh-questioned, relativized, cliticized for French etc.), but also for all the valency alternations allowed for the subcategory frame concerned (here, passive with/without agent, causative etc). Therefore, there is no need to generate usual LFG lexical rules, and the absence of lexical rules has no effect on interfacing the grammars we generate with existing LFG parsers. Fig. 4 illustrates the generation of a decorated tree for passive-with-no-agent.", "cite_spans": [ { "start": 356, "end": 372, "text": "(Kameyama, 1986)", "ref_id": null }, { "start": 1142, "end": 1166, "text": "(Dalrymple et al., 1995)", "ref_id": "BIBREF10" } ], "ref_spans": [ { "start": 2371, "end": 2377, "text": "Fig. 4", "ref_id": "FIGREF0" } ], "eq_spans": [], "section": "Figure 3: LFG Rule and a lexical entry", "sec_num": null }, { "text": "When generating TAGs and LFGs from a single MG hierarchy, we must make sure that long-distance phenomena are correctly handled. The only difference between TAG and LFG is that for TAG, we must make sure that bridge verbs are auxiliary trees, i.e. have a foot node, whereas for LFG we must make sure that extraction rules have a node decorated with a functional uncertainty equation. In TAGs, long -Shanker, 1989) . Figure 5 illustrates the TAG analysis of What did Mary say that John ate: the extracted element is in the same grammar rule as its predicate \"ate\" 15 and the tree anchored by the bridge verb is inserted in the \"ate\" tree thanks to the adjunction operation. ", "cite_spans": [ { "start": 397, "end": 412, "text": "-Shanker, 1989)", "ref_id": null } ], "ref_spans": [ { "start": 415, "end": 423, "text": "Figure 5", "ref_id": null } ], "eq_spans": [], "section": "Long distance dependencies", "sec_num": "5" }, { "text": "Sy N Po (What) S2 Aux (did) N Px (Mary) V Px Vx (say) Sbarx Compl (that) Sx N Ps (John) V", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Long distance dependencies", "sec_num": "5" }, { "text": "A first advantage of using a MetaGrammar, discussed in (Kinyon and Prolo, 2002) , is that the syntactic phenomena covered are quite systematic: if rules are generated for \"transitive-passive-whExtractedByPhrase\" (e.g. By whom was the mouse eaten), and if the hierarchy includes ditransitive verbs, then the automatic crossing of phenomena ensures that sentences will be generated for \"ditransitive-passive-whExtractedByPhrase\" (i.e. By whom was Peter given a present). All rules for word order variations are automatically generated by underspecifying relations between quasi-nodes in the MG hierarchy (e.g. precedence relation between first and second object for ditransitives in French). A second advantage of the MG is to minimize the need for human intervention in the grammar development process. Humans encode the linguistic knowledge in a compact manner i.e. the MG hierarchy, and then verify the validity of the rules generated. If some grammar rules are missing or incorrect, then changes are made directly in the MG hierarchy and never in the generated rules 17 . This ensures a homogeneity not necessarily present with traditional hand-crafted grammars. A third and essential advantage is that it is straightforward to obtain from a single hierarchy parallel multi-lingual grammars similar to the parallel LFG grammars presented in (Butt et al., 1999) and (Butt et al., 2002) , but with an explicit sharing 17 Exceptionality is handled in the MG hierarchy as well. We do not have much to say about it: only that the MG does not impose any additional burden to handle syntactic \"exceptions\" compared to hand-crafted grammars. of classes 18 in the MetaGrammar hierarchy plus a cross-framework application. 19", "cite_spans": [ { "start": 55, "end": 79, "text": "(Kinyon and Prolo, 2002)", "ref_id": null }, { "start": 1343, "end": 1362, "text": "(Butt et al., 1999)", "ref_id": "BIBREF4" }, { "start": 1367, "end": 1386, "text": "(Butt et al., 2002)", "ref_id": "BIBREF5" } ], "ref_spans": [], "eq_spans": [], "section": "Advantages of a MetaGrammatical level", "sec_num": "6" }, { "text": "So far, we have implemented a non trivial hierarchy which consists of 189 classes. A fragment of the hierarchy is shown in Figure 8 . From this hierarchy, we generate 550 decorated trees, which correspond to approx. 550 TAG trees and 140 LFG rules. We cover the following syntactic phenomena: 50 verb subcategorization frames (including auxiliaries, modals, sentential and infinitival complements), dative-shift for English, clitics (and their placement) for French, passives with and without agent, long distance dependencies (relatives, wh-questions, clefts) and a few idiomatic expressions. A more detailed presentation of the LFG grammar is presented in (Cl\u00e9ment and Kinyon, 2003) . A more detailed discussion of the cross-language aspects with a comparison to related work such as the LFG ParGram project, or HPSG matrix grammars (Bender et al., 2002) ", "cite_spans": [ { "start": 658, "end": 684, "text": "(Cl\u00e9ment and Kinyon, 2003)", "ref_id": "BIBREF8" }, { "start": 835, "end": 856, "text": "(Bender et al., 2002)", "ref_id": "BIBREF1" } ], "ref_spans": [ { "start": 123, "end": 131, "text": "Figure 8", "ref_id": null } ], "eq_spans": [], "section": "Cross-language and -framework generation", "sec_num": "7" }, { "text": "We have presented a MetaGrammar tool which allows us to automatically generate parallel TAG and LFG grammars for English and French. We have discussed the handling of long-distance dependencies. We keep enriching our hierarchy in order to 18 To the best of our knowledge, (Butt et al., 2002) apply similar linguistic choices for grammars in different languages when possible, but do not explicitly resort to rule-sharing.", "cite_spans": [ { "start": 239, "end": 241, "text": "18", "ref_id": null }, { "start": 272, "end": 291, "text": "(Butt et al., 2002)", "ref_id": "BIBREF5" } ], "ref_spans": [], "eq_spans": [], "section": "Conclusion", "sec_num": "8" }, { "text": "19 (Kinyon and Rambow, 2003b) have used the tool to generate from a single hierarchy cross-framework and cross-language annotated test-suites, including English and German sentences annotated for F-structure, as well as for constituent and dependency structure 20 The main difference with HPSG approaches such as Matrix is that HPSG type-hierarchies are an inherent part of the grammar, and deal only with one framework:HPSG, whereas our MG hierarchy is not an inherent part of the grammar, since it is used to generate cross-framework grammars offline. 21 We use binary features in order to add more languages and frameworks to the hierarchy. E.g. when adding German, some classes are shared for English and German, but not French and are marked [English=+;German=+;French=-]. This would not be possible if we had a non binary feature [Language=X] . The same reasoning applies for generating additional frameworks. increase the coverage of our grammars, are adding new languages (German) and exploring the extension of the domain of locality to sentence level (Kinyon and Rambow, 2003a) . The ultimate goal of this work is twofold: first, to maximize cross-language rule-sharing at the metagrammatical level; Second, to automatic extract MetaGrammars from a treebank (Kinyon, 2003) , and then automatically generate grammars for different frameworks.", "cite_spans": [ { "start": 3, "end": 29, "text": "(Kinyon and Rambow, 2003b)", "ref_id": null }, { "start": 261, "end": 263, "text": "20", "ref_id": null }, { "start": 554, "end": 556, "text": "21", "ref_id": null }, { "start": 836, "end": 848, "text": "[Language=X]", "ref_id": null }, { "start": 1061, "end": 1087, "text": "(Kinyon and Rambow, 2003a)", "ref_id": null }, { "start": 1268, "end": 1282, "text": "(Kinyon, 2003)", "ref_id": "BIBREF8" } ], "ref_spans": [], "eq_spans": [], "section": "Conclusion", "sec_num": "8" }, { "text": "We assume the reader has a basic knowledge of TAGs and LFGs and refer respectively to(Joshi, 1987) and(Bresnan and Kaplan, 1982) for an introduction to these frameworks.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "A Similar MetaGrammar type of organization for TAGs was independently presented in(Xia, 2001) for English.3 This terminal class may be the result of the crossing of several super-classes, to handle complex phenomena such as Pas-sive+Causative.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "We also generate Range Concatenation Grammars(Boullier, 1998), but do not develop this point here.5 The notion of HyperTag was inspired by that of supertags(Srinivas, 1997), which consists in assigning a TAG elementary tree to lexical items, hence enriching traditional POS tagging. However, HyperTags are framework-independent.6 This compiler is freely available on http://www.loria.fr/equipes/led/outils/mgc/mgc.html", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "We have augmented the tool to support free variables for nodes, optional resources, as well as additional relations such as sister and c-command. We do not detail these technical points for sake of brevity.8 Another way to see this is by analogy to a resource allocation graph.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "This can be compared to computer programs written in Perl, which are easy to develop, but hard to read and maintain. A", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "Non terminal symbols symbols are renamed and, in a second phase, rules which differ only by the name of their non terminals are merged, in a manner similar to that used in(Hepple and van Genabith, 2000). For space reasons, we do not detail the algorithm here.13 We use the freely available XLFG parser described in(Cl\u00e9ment and Kinyon, 2001) and have also experimented with the Xerox parser(Kaplan and Maxwell, 1996).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "Or, alternatively, some notion of lexical mapping, which we do not discuss here.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "Although a trace is present in rule for \"ate\", following the convention of the Xtag project, it is not compulsory and not needed from a formal point of view.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null }, { "text": "Because the MG does not impose a restricted domain of locality,(Kinyon, 2003) proposes an alternative to functional uncertainty, which we do not present here for space reasons.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "", "sec_num": null } ], "back_matter": [ { "text": "The extracted element (node NP o in rule 4) is associated to a function path (in bold characters), which is unknown since an arbitrary number of clauses can appear between \"NP o \" and its regent (V y in rule 6). The result of the LFG analysis for What did M. say that J. ate, using this standard LFG grammar is shown in Figure 6 . A constituent structure is built using the the rewriting rules. The functional equations associated to nodes compute an F-structure which ensures that each predicate of the sentence (i.e. \"say\" and \"ate\") have their arguments realized. The need for functional uncertainty results from the fact that in LFG, contrary to TAGs, the extracted element (NP o ) and its governor (V y ) are located in different grammar rules. Hence, when generating LFGs, we must make sure that the decorated tree bears a functional uncertainty equation at the site of the extraction. 7 illustrates the generation of such a decorated tree (identical to the TAG tree for \"ate\" modulo the functional equations), which will be decomposed into rules 4, 5 and 6. 16 ", "cite_spans": [], "ref_spans": [ { "start": 320, "end": 328, "text": "Figure 6", "ref_id": null } ], "eq_spans": [], "section": "annex", "sec_num": null } ], "bib_entries": { "BIBREF0": { "ref_id": "b0", "title": "FTAG: current status and parsing scheme", "authors": [ { "first": "A", "middle": [], "last": "Abeill\u00e9", "suffix": "" }, { "first": "M", "middle": [], "last": "Candito", "suffix": "" }, { "first": "A", "middle": [], "last": "Kinyon", "suffix": "" } ], "year": 1999, "venue": "Proc. Vextal-99", "volume": "", "issue": "", "pages": "", "other_ids": {}, "num": null, "urls": [], "raw_text": "A. Abeill\u00e9, M. Candito, and A. Kinyon. 1999. 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