Lexical rules

  The approach presented here requires there to be different lexical rules for different types of adjunction. Each rule allows for the integration of semantics and structure-sharing between modifier and modified appropriate to the relevant type of adjunction. The design of the rules essentially follows that of vannoord_bouma:94, in that the add_adj_control rule builds an output structure based on the input structure it receives, by relying on other rules to modify elements of the structure in appropriate ways.

The basic algorithm for extending the subcat list of the main verb in a sentence can be summarised as follows:

1. Take the main verb's subcat list as specified in its lexical entry.
2. Append adjuncts to the end of the subcat list.
   1. Add at most one pseudo-complement, if semantically compatible with the verbal relation.
   2. Add any number of thematic adjuncts and integrate their semantics immediately into the verb's sit-desc.
   3. Add any number of restrictive adjuncts and integrate their semantics immediately into the verb's sit-desc.
   4. Add any number of operator adjuncts to the subcat list (in surface order). Also add this adjunct to the op-adj list in order of semantic obliqueness relative to other operator adjuncts already represented on that list as determined by the function eval_sem_obliqueness (not worked out below).
3. Process the semantics of any operator adjuncts added (as outlined in the previous section).

The application of the lexical rules depends on dynamic interaction with the parsing mechanisms through delayed evaluation techniques, as outlined in van Noord and Bouma (1994) and briefly introduced in Section 3.4.4. The lexical rules here can be seen as defining potential licensed additions to a verb's subcat list, which can be actualised during the processing (parsing) of actual sentences.

The rules are described and presented in detail below. Note that the subsort check needed to prevent redundant thematic PPs is not explicitly represented, nor is the definition of process_op_adjs. The definition of the function eval_sem_obliqueness is left out, as it is beyond the scope of this chapter to determine precisely what the constraints on relative semantic obliqueness of operator adjuncts are.

Each clause of the function add_adj as defined below is a lexical rule which adds just one adjunct, of a particular adjunct type, at a time, and then recursively calls the function add_adj to allow the addition of any number of other adjuncts (which might be none). In this way adjuncts of different types can be interspersed with one another.

• Controlling rule: allows for the addition of all adjuncts to the element's SUBCAT list, and the processing of all operator adjuncts. The first argument is the original synsem object input, the second argument is the synsem object which results after all adjuncts have been added and processed. This rule calls process_op_adjs, which is responsible for processing the semantic contribution of the operator adjuncts and integrating it to establish the full semantics expressed in the sentence (SemanticsOut).

  

• Top level rule used in the addition of adjuncts: forces all adjuncts to be added to the SUBCAT list after all complements. This clause applies when there are no more pseudo-complements to be added.

  

• Top level rule which licenses the addition of a pseudo-complement prior to any other adjuncts. The rule specifies the unification of the thematic information added by the pseudo-complement with the verb's default internal thematic element. This adds the information contributed by the pseudo-complement into the existing representation of the verb's internal semantics, if it is compatible (see Section 3.3.3). It then makes a recursive call to add_adj_top to allow for the addition of subsequent pseudo-complements prior to any other adjuncts.

  

• Base case for adding adjuncts - adds no adjunct, and the output semantics is unified with the input semantics. The argument structure for this function is:
  add_adj(Head, Adjuncts, SemanticsIn, SemanticsOut, Operator-adjsIn, Operator-adjsOut).

  add_adj(, , Semantics , Semantics , Operator-adjs , Operator-adjs ).

• Adds a thematic adjunct; specifies the unification of the thematic information added by the adjunct with the situational (external) thematic elements, adding the information into the representation of the situation as a whole. This clause handles both pure thematic adjuncts and the event-modifying use of pc/adj PPs.

  

• Adds a restrictive adjunct; specifies that the sit-desc object found in the SYNSEM:LOC:CONT:NUC field of the adjunct definition becomes the semantics associated with the current situation, on the basis of the assumption that for restrictive adjuncts the change to the semantics of the modified situation is fully specified in the lexical entry.

  

• Adds an operator adjunct to both the adjuncts list and the operator-adjuncts list. Function eval_sem_oblique evaluates the semantic obliqueness of this adjunct with respect to other elements of the operator-adjuncts list and inserts it in the appropriate place ( is the synsem value associated with the adjunct, is the original op-adj list and is the modified op-adj list). Does not change the semantics associated with the current situation, as the integration of the semantics contributed by the operator adjunct will take place at the end of the addition of adjuncts, in process_op_adjs.