The GF Resource Grammar Library The GF Resource Grammar Library contains grammar rules for 10 languages (some more are under construction). Its purpose is to make these rules available for application programmers, who can thereby concentrate on the semantic and stylistic aspects of their grammars, without having to think about grammaticality. To give an example, an application dealing with music players may have a semantical category ``Kind``, examples of Kinds being Song and Artist. In German, for instance, Song is linearized into the noun "Lied", but knowing this is not enough to make the application work, because the noun must be produced in both singular and plural, and in four different cases. By using the resource grammar library, it is enough to write lin Song = reg2N "Lied" "Lieder" neuter and the eight forms are correctly generated. The use of the resource grammar extends from lexical items to syntax rules. The application mught also want to modify songs with properties, such as "American", "old", "good". The German grammar for adjectival modifications is particularly complex, because the adjectives have to agree in gender, number, and case, also depending on what determiner is used ("ein Amerikanisches Lied" vs. "das Amerikanische Lied"). All this variation is taken care of by the resource grammar function fun AdjCN : AP -> CN -> CN and the resource grammar implementation of the rule adding properties to kinds is lin PropKind kind prop = AdjCN prop kind given that lincat Prop = AP lincat Kind = CN The resource library API is devided into language-specific and language-independet parts. To put is roughly, - syntax is language-independent - lexicon is language-specific Thus, to render the above example in French instead of German, we need to pick a different linearization of Song, lin Song = regGenN "chanson" feminine But to linearize PropKind, we can use the very same rule as in German. The resource function AdjCN has different implementations in the two languages, but the application programmer need not care about the difference. ==To use a resouce grammar== ===Parsing=== The intended use of the resource grammar is as a library for writing application grammars. It is not designed for e.g. parsing text. There are several reasons why this is not so practical: - efficiency: the resource grammar uses complex data structures, in particular, discontinuous constituents, which make parsing slow and the parser size huge - completeness: the resource grammar does not necessarily cover all rules of the language - only enough many so that it is possible to express everything in one way or another - lexicon: the resource grammar has a very small lexicon, only meant for test purposes - semantics: the resource grammar has very little semantic control, and may accept strange input or deliver strange interpretations - ambiguity: parsing in the resource grammar may return lots of results many of which are implausible All of these problems should be settled in application grammars - the very point of resource grammars is to isolate the low-level linguistic details such as inflection, agreement, and word order, from semantic questions, which is what the application grammarians should solve. ===Inflection paradigms=== The inflection paradigms are defined separately for each language L in the module ParadigmsL. To test them, the command cc (= compute_concrete) can be used: > i -retain german/ParadigmsGer.gf > cc regN "Schlange" { s : Number => Case => Str = table Number { Sg => table Case { Nom => "Schlange" ; Acc => "Schlange" ; Dat => "Schlange" ; Gen => "Schlange" } ; Pl => table Case { Nom => "Schlangen" ; Acc => "Schlangen" ; Dat => "Schlangen" ; Gen => "Schlangen" } } ; g : Gender = Fem } ===Syntax rules=== Syntax rules should be looked for in the abstract modules defining the API. There are around 10 such modules, each defining constructors for a group of one or more related categories. For instance, the module Noun defines how to construct common nouns, noun phrases, and determiners. Thus the proper place to find out how nouns are modified with adjectives is Noun, because the result of the construction is again a common noun. Browsing the libraries is helped by the gfdoc-generated HTML pages. However, this is still not easy, and the most efficient way is probably to use the parser. Even though parsing is not an intended end-user application of resource grammars, it is a useful technique for application grammarians to browse the library. To find out what resource function does some particular job, you can just parse a string that exemplifies this job. For instance, to find out how sentences are built using transitive verbs, write > i english/LangEng.gf > p -cat=Cl -fcfg "she loves him" PredVP (UsePron she_Pron) (ComplV2 love_V2 (UsePron he_Pron)) Parsing with the English resource grammar has an acceptable speed, but with most languages it takes just too much resources even to build the parser. However, examples parsed in one language can always be linearized in other languages: > i italian/LangIta.gf > l PredVP (UsePron she_Pron) (ComplV2 love_V2 (UsePron he_Pron)) lo ama ==Overview of linguistic structures== The outermost linguistic structure is Text. Texts are composed from Phrases followed by punctuation marks - either of ".", "?" or "!! (with their proper variants in Spanish and Arabic). Here is an example of a Text. John walks. Why? He doesn't want to sleep! Phrases are mostly built from Utterances, which in turn are declarative sentences, questions, or imperatives - but there are also "one-word utterances" consisting of noun phrases or other subsentential phrases. Some Phrases are more primitive, for instance "yes" and "no". Here are some examples of Phrases. yes come on, John but John walks give me the stick please don't you know that he is sleeping a glass of wine a glass of wine please There is no connection between the punctuation marks and the types of utterances. This reflects the fact that the punctuation mark in a real text is selected as a function of the speech act rather than the grammatical form of an utterance. The following text is thus well-formed. John walks. John walks? John walks! What is the difference between Phrase and Utterance? Just technical: a Phrase is an Utterance with an optional leading conjunction ("but") and an optional tailing vocative ("John", "please"). The richest of the categories below Utterance is S, Sentence. A Sentence is formed from a Clause, by fixing its Tense, Anteriority, and Polarity. The difference between Sentence and Clause is thus also rather technical. For example, each of the following strings has a distinct syntax tree of category Sentence: John walks John doesn't walk John walked John didn't walk John has walked John hasn't walked John will walk John won't walk ... whereas in the category Clause all of them are just different forms of the same tree. The following syntax tree of the Text "John walks." gives an overview of the structural levels. Node Constructor Type of subtree Alternative constructors 1. TFullStop : Text TQuestMark 2. (PhrUtt : Phr 3. NoPConj : PConj but_PConj 4. (UttS : Utt UttQS 5. (UseCl : S UseQCl 6. TPres : Tense TPast 7. ASimul : Anter AAnter 8. PPos : Pol PNeg 9. (PredVP : Cl 10. (UsePN : NP UsePron, DetCN 11. john_PN) : PN mary_PN 12. (UseV : VP ComplV2, ComplV3 13. walk_V)))) : V sleep_V 14. NoVoc) : Voc please_Voc 15. TEmpty : Text Here are some examples of the results of changing constructors. 1. TFullStop -> TQuestMark John walks? 3. NoPConj -> but_PConj But John walks. 6. TPres -> TPast John walked. 7. ASimul -> AAnter John has walked. 8. PPos -> PNeg John doesn't walk. 11. john_PN -> mary_PN Mary walks. 13. walk_V -> sleep_V John sleeps. 14. NoVoc -> please_Voc John sleeps please. All constructors cannot of course be changed so freely, because the resulting tree would not remain well-typed. Here are some changes involving many constructors: 4- 5. UttS (UseCl ...) -> UttQS (UseQCl (... QuestCl ...)) Does John walk? 10-11. UsePN john_PN -> UsePron we_Pron We walk. 12-13. UseV walk_V -> ComplV2 love_V2 this_NP John loves this. The linguistic phenomena mostly discussed in traditional grammars and modern syntax belong to the level of Clauses, that is, lines 9-13, and occasionally to Sentences, lines 5-13. At this level, the major categories are NP (Noun Phrase) and VP (Verb Phrase). A Clause typically consists of a NP and a VP. The internal structure of both NP and VP can be very complex, and these categories are mutually recursive: not only can a VP contain an NP, [VP loves [NP Mary]] but an NP can also contain a VP [NP every man [RS who [VP walks]]] (a labelled bracketing like this is of course just a rough approximation of a GF syntax tree, but still a useful device of exposition). Most of the resource modules thus define functions that are used inside NPs and VPs. Here is a brief overview: Noun: How to construct NPs. The main three mechanisms for constructing NPs are - from proper names: John - from pronouns: we - from common nouns by determiners: this man The Noun module also defines the construction of common nouns. The most frequent ways are - lexical noun items: man - adjectival modification: old man - relative clause modification: man who sleeps Verb: How to construct VPs. The main mechanism is verbs with their arguments: - one-place verbs: walks - two-place verbs: loves Mary - three-place verbs: gives her a kiss - sentence-complement verbs: says that it is cold - VP-complement verbs: wants to give her a kiss A special verb is the copula, "be" in English but not even realized by a verb in all languages. A copula can take different kinds of complement: - an adjectival phrase: (John is) old - an adverb: (John is) here - a noun phrase: (John is) a man The resource modules are named after the kind of phrases that are constructed in them, and they can be roughly classified by the "level" or "size" of expressions that are formed in them: - Larger than sentence: Text, Phrase - Same level as sentence: Sentence, Question, Relative - Parts of sentence: Adjective, Adverb, Noun, Verb - Cross-cut: Conjunction Because of mutual recursion such as embedded sentences, this classification is not a complete order. However, no mutual dependence is needed between the modules in a formal sense, but they can all be compiled separately. This is due to the module Cat, which defines the type system common to the other modules. For instance, the types NP and VP are defined in Cat, and the module Verb only needs to know what is given in Cat, not what is given in Noun. To implement a rule such as Verb.ComplV2 : V2 -> NP -> VP it is enough to know the linearization type of NP (given in Cat), not what ways there are to build NPs (given in Noun), since all these ways must conform to the linearization type defined in Cat.