more overview of linguistic structures

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 The GF Resource Grammar Library
 
+==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.
+example of a Text.
 
   John walks. Why? He doesn't want to sleep!
 
@@ -29,3 +31,135 @@ 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                     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.