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Vererbung

Vererbung. Prolog Aufbaukurs SS 2000 Heinrich-Heine-Universität Düsseldorf Christof Rumpf. Interpretieren vs. Kompilieren. Eine Typensignatur enthält implizit viele Relationen. Ein Interpreter macht diese Relationen explizit. Laufzeit-, Runtime-, bzw. Online-Berechnung

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Vererbung

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  1. Vererbung Prolog Aufbaukurs SS 2000 Heinrich-Heine-Universität Düsseldorf Christof Rumpf

  2. Interpretieren vs. Kompilieren • Eine Typensignatur enthält implizit viele Relationen. • Ein Interpreter macht diese Relationen explizit. • Laufzeit-, Runtime-, bzw. Online-Berechnung • Ein Compiler berechnet (alle) Relationen vollständig und liefert das Ergebnis der Berechnung zum direkten Zugriff. • Kompilezeit-, Compiletime-, bzw. Offline-Berechnung Typinferenz

  3. Kompilierung der Signatur compile_signature:- complete_signature_syntax, % insert empty subtype/feature lists define_undefined_types, % with empty subtype/feature lists connect_homeless_types, % they become subtypes of top no_multiple_type_definitions, % instead of merging together no_cycles, % with respect to subtype relation cp_ist, % immediate subtypes cp_subtypes, % subtypes cp_lbs, % lower bounds cp_glbs, % greatest lower bounds cp_ubs, % upper bounds cp_lubs, % least upper bounds no_bcpo, % bounded complete partial order check cp_flubs, % least upper bounds for features feature_inheritance, % with respect to subtype relation cp_fss. % construct feature structures Typinferenz

  4. Syntax-Komplettierung complete_signature_syntax:- complete_subtype_lists, complete_feature_lists, !. complete_feature_lists:- (S=[] ; S=[_|_]), retract((T >> S)), assert((T >> S :: [])), fail. complete_feature_lists. complete_subtype_lists:- retract((T :: F)), assert((T >> [] :: F)), fail. complete_subtype_lists. Typinferenz

  5. Undefinierte Typen % define_undefined_types/0 % Every subtype of a defined type and every feature % value that is itself undefined gets a default definition % with empty sets of immediate subtypes and features. define_undefined_types:- immediate_subtypes(SubTypes), all_feature_values(Values), append(SubTypes,Values,Candidates), define_undefined_types(Candidates), !. define_undefined_types([]):- !. define_undefined_types([H|T]):- type(H), !, define_undefined_types(T). define_undefined_types([H|T]):- assert((H >> [] :: [])), define_undefined_types(T). Typinferenz

  6. Heimatlose Typen: Folge 1 % connect_homeless_types/0 % Every defined type that is not defined as a subtyp of some other type % becomes an immediate subtype of 'top'. If top is not defined, it gets % introduced as the common supertype of all other types in the lattice, % that will be bounded in that course. connect_homeless_types:- types(Types), immediate_subtypes(SubTypes), connect_homeless_types(Types,SubTypes), !. connect_homeless_types(Types,SubTypes):- connect_homeless_types(Types,SubTypes,HomelessTypes), connect_homeless_types(HomelessTypes), !. Typinferenz

  7. Heimatlose Typen: Folge 2 connect_homeless_types([],_,[]):- !. connect_homeless_types([H|T],ST,Homeless):- (H = top ; member(H,ST)), !, connect_homeless_types(T,ST,Homeless). connect_homeless_types([H|T],ST,[H|Homeless]):- connect_homeless_types(T,ST,Homeless). connect_homeless_types(Homeless):- retract((top >> SubTypes :: Features)), !, append(SubTypes,Homeless,CompletedSubTypes), assert((top >> CompletedSubTypes :: Features)). connect_homeless_types(Homeless):- asserta((top >> Homeless :: [])). Typinferenz

  8. Multiple Typdefinitionen no_multiple_type_definitions:- multiple_type_definitions(Multiples), m_t_d(Multiples), !. m_t_d([]):- !. m_t_d(Multiples):- nl, write('- ERROR - multiple definitions for type(s): '), nl, write(Multiples), nl, !. multiple_type_definitions(Multiples):- bagof(Type, type(Type), Types), list_duplicates(Types, Multiples). list_duplicates([],[]):- !. list_duplicates([H|T1],[H|T2]):- member(H,T1), !, list_duplicates(T1,T2). list_duplicates([H|T],Multiples):- list_duplicates(T,Multiples). Typinferenz

  9. Zyklen no_cycles:- cycles(Cycles), report_cycles(Cycles). cycles(Cycles):- types(Types), cycles(Types,Cycles). cycles([],[]):- !. cycles([Type|Types],[Cycle|Cycles]):- cycle(Type,Cycle), !, Cycle = [_|CTypes], difference(Types,CTypes,DTypes), cycles(DTypes,Cycles). cycles([_|Types],Cycles):- cycles(Types,Cycles). cycle(Type,Cycle):- type(Type), connected(Type,Type,Cycle). Typinferenz

  10. Pfade connected(SuperType,SubType,Path):- type(SuperType), type(SubType), connected(SuperType,SubType,[],RPath), reverse([SubType|RPath],Path). connected(Type1,Type2,Path,[Type1|Path]):- immediate_supertype(Type1,Type2), !. connected(Type,_,Visited,_):- member(Type,Visited), !, fail. connected(Type1,Type2,Visited,Path):- immediate_supertype(Type1,Type3), connected(Type3,Type2,[Type1|Visited],Path). Typinferenz

  11. Meldung: Zyklen report_cycles([]):- !. report_cycles([Cycle|Cycles]):- report_cycle(Cycle), report_cycles(Cycles). report_cycle(Types):- write('- ERROR - type inheritance cycle: '), write(Types), nl. Typinferenz

  12. Subtypen cp_subtypes:- retractall(db_subtype(_,_)), subtype(A,B), enter(db_subtype(A,B)), fail. cp_subtypes. enter(Clause):- call(Clause), !. enter(Clause):- assert(Clause). Typinferenz

  13. BCPO-Check no_bcpo:- setof1((A,B), C^(db_glb(A,B,C),A @< B), ABs), member((A,B),ABs), nuglb(A,B,GLBs), write('- ERROR - multiple greatest lower bounds: '), nl, tab(5), write(T1 + T2 = GLBs), nl, fail. no_bcpo. nuglb(A,B,GLBs):- setof(C, db_glb(A,B,C), GLBs), GLBs = [_,_|_], !. Typinferenz

  14. Feature-LUBs I cp_flubs:- retractall(db_feature_lub(_,_)), feature_lubs(FLUBs), cp_flubs(FLUBs), !. cp_flubs([]):- !. cp_flubs([FLUB|FLUBs]):- FLUBPred =.. [db_feature_lub|FLUB], assert(FLUBPred), cp_flubs(FLUBs). Typinferenz

  15. Feature-LUBs II feature_lub(Feature:Val,Type):- feature(_,Feature:_), setof(T, V^feature(T,Feature:V),Types), lubs(Types,LUBs), member(Type,LUBs), feature(Type,Feature:Val). feature_lubs(FLUBs):- setof1([F:V,T], feature_lub(F:V,T),FLUBs). Typinferenz

  16. Vererbung % feature_inheritance/0 % All types inherit the features of their supertypes through % manipulation of the type signature in the dynamic database. % Features are inherited top down, depth first, left to right. feature_inheritance:- call(top >> SubTypes :: Feats), expand_types(SubTypes,Feats), !. Typinferenz

  17. Typ-Expansion durch Vererbung % expand_types(+Types,+Feats) % Every type in the list Types inherits the feature value pairs in Feats. expand_types([],_). expand_types([H|T],Feats):- expand_type(H,Feats), expand_types(T,Feats). % expand_type(+Type,+Feats) % Type and all it's subtypes inherit the feature value pairs in Feats. expand_type(T,IFeats):- retract((T >> Subtypes :: TFeats)), inherit_features(TFeats,IFeats,UFeats,T), assert((T >> Subtypes :: UFeats)), !, expand_types(Subtypes,UFeats). Typinferenz

  18. Merkmalsvererbung % inherit_features(+LocalFeats,+InheritedFeats,-UnifiedFeats,+Type). % LocalFeats of Type and InheritedFeats are merged to UnifiedFeats. If an % attribute occurs in both LocalFeats and InheritedFeats, the consistency of % their values is checked. If the values are inconsistent, UnifiedFeats gets % the local feature value and an error message is printed onto the screen. % If their values are consistent, UnifiedFeats gets the greatest lower bound % as the value for that attribute. inherit_features([],F,F,_). inherit_features([F:V1|F1],F2,F3,T):- delete(F:V2,F2,F21), !, check_value_consistency(V1,V2,V3,F,T), inherit_features(F1,[F:V3|F21],F3,T). inherit_features([F:V|F1],F2,F3,T):- inherit_features(F1,[F:V|F2],F3,T). Typinferenz

  19. Konsistenz-Check check_value_consistency(V1,V2,V3,F,T):- glb(V1,V2,V3), !. check_value_consistency(V1,V2,V1,F,T):- nl, write('- ERROR - inconsistent feature inheritance'), nl, tab(5), write('for type: '), write(T), nl, tab(5), write('at feature: '), write(F), nl, tab(5), write('local value: '), write(V1), nl, tab(5), write('inherited value: '), write(V2), nl. Typinferenz

  20. Merkmalsstrukturen I cp_fss:- abolish(db_fs/2), type(T), cp_fs(T,FS,[]), assert(db_fs(T,FS)), fail. cp_fss. cp_fs(Type, _-Type=FS, Types):- call(Type >> _ :: Features), cp_construct_feature_structure(Features,FS,[Type|Types]), !. Typinferenz

  21. Merkmalsstrukturen II cp_construct_feature_structure([],[],_). cp_construct_feature_structure([F:V|FVs],[F:(_-V=[])|FVFSs],Ts):- member(V,Ts), !, write('ERROR: cyclic feature structure for type '), write(V), nl, cp_construct_feature_structure(FVs,FVFSs,Ts). cp_construct_feature_structure([F:V|FVs],[F:VFS|FVFSs],T):- get_fs(V,VFS,T), cp_construct_feature_structure(FVs,FVFSs,T). get_fs(T,FS,_):- call(db_fs(T,_)), !, db_fs(T,FS). get_fs(T,FS,Ts):- cp_fs(T,FS,Ts). Typinferenz

  22. Literatur • Carpenter, Bob (199?): The Logic of Typed Feature Structures. • O‘Keefe, Richard (199?): The Craft of Prolog. Typinferenz

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