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Reentrancies
The second relaxation is not without ramifications for the organization of a transfer grammar. This relaxation has to do with reentrancies in feature structures. Some constructions such as control verbs and relative clauses may be represented using reentrancies; for example `the soldiers tried to shoot the president' may be represented by a feature structure where the first argument of `try' is reentrant with the first argument of `shoot', cf. figure 7.
Figure 7: A logical form containing reentrancy
The translation of such logical forms to Dutch equivalents can be defined as in rule 8.
Translating subject controlreent
0 
1 2 3
0 gb pred
= 1 gb
0 nl pred = 1 sp
0 gb arg1 = 0 gb arg2 arg1
0 nl arg1 = 0 nl arg2 arg1
0 gb arg1 = 2 gb
0 nl arg1 = 2 sp
0 gb arg2 = 3 gb
0 nl arg2 = 3 sp
In this rule the reentrancy is explicitly mentioned for two reasons. The first
reason is simply that in the case of different possible translations of 
we want the
same translation for both and the embedded .
Note that the translation
of `soldier' into Dutch can be both `soldaat' or `militair'. If the reentrancy is not
mentioned the system
has to try to generate from four different Dutch logical forms, two of which without matching 's.
The reentrancy is also mentioned because this is required by the completeness condition. It is possible to relax the completeness and coherence condition with respect to these reentrancies, again without affecting the reversibility properties of the system by slightly changing the definition of equivalence. There is a trade-off between simplicity of the transfer grammar (in the presence of this relaxation) and the efficiency of the system. In the case of this relaxation the system will eventually find the good translations, but it may take a while. On the other hand, if we are to mention all (possibly unbounded) reentrancies explicitly then the transfer grammar will have to be complicated by a threading mechanism to derive such reentrancies. Again, the specific use of reentrancies in the logical forms that are defined will determine whether this relaxation is desired or not.
Next: Final remarks Up: Possible relaxations Previous: Cyclic and non-cyclic
Gertjan van Noord
Fri Nov 25 13:42:02 MET 1994