Example semantic structures

The techniques to compute the relation between phonological and semantic structures (in parsing and generation), and between semantic structures of different languages (in machine translation) are supposed to abstract away from the particularities of these phonological and semantic structures. However, for concreteness and expository purposes I will define very simple semantic structures which are used throughout the example grammars and rules in this thesis. These semantic structures are feature structures, of the sort to be introduced in chapter 2. The reader unfamiliar with feature structures is advised to consult that chapter first.

The semantic structures to be described here are essentially predicate argument structures decorated with some syntactic features. Similar structures were used in the MiMo2 translation prototype (this prototype is described in [103,104], and in chapter 5). Semantic structures come in several `sorts'. A semantic structure has a label sort of which the value is one of

$$\{\mbox{\rm nullary}, \mbox{\rm unary}, \mbox{\rm binary}, \mbox{\rm ternary}, \mbox{\rm modifier}\}$$
Other attributes of semantic structures include pred, mod, arg1, arg2 and arg3 of which the values are semantic structures themselves. The convention is that structures with sort ` ternary' are specified for arg1, arg2 and arg3, whereas structures with sort ` binary' are not specified for arg3, and so on. The attribute pred takes constants as its values (these constants often represent content words). Furthermore semantic structures are decorated with labels such as neg, number, tense, aspect, def,...of which the values are atomic and of which the intention will be clear. These syntactic labels play a minor role in this thesis, and are often left out. For example, the sentence `the priest drinks wine' is associated with argument structure:

$$\avm{ \mbox{\it sort}: \mbox{\rm binary}\\ \mbox{\it pred}:... ...se}: \mbox{\rm present}\\ \mbox{\it neg}: \mbox{\rm nonneg} }$$
Furthermore, modifier structures such as noun-adjective constructions are represented by a semantic structure of sort `modifier', with labels mod and arg1 of which the values are semantic structures. Therefore, the semantic structure of a noun phrase `very strong whisky', may look as follows:

$$\avm{ \mbox{\it sort}: \mbox{\rm modifier}\\ \mbox{\it mod}... ... \mbox{\rm indef}\\ \mbox{\it number}: \mbox{\rm mass} } }$$
As a more complex example the logical form of

is the following feature structure:

$$\avm{ \mbox{\it sort}: \mbox{\rm binary}\\ \mbox{\it pred}... ...number}: \mbox{\rm sg}}}}\\ \mbox{\it neg}: \mbox{\rm neg} }$$

To encode for example control relations I introduce a special semantic structure of which the sort is ` refer' and of which the only other attribute is index. Furthermore, other semantic structures may also be specified for the index attribute. Sharing of the index attribute then can be used to indicate control, as in the following example for the sentence

$$\avm{ \mbox{\it sort}: \mbox{\rm binary} \\ \mbox{\it pred... ...hisky\_priest}\\ \mbox{\it number}: \mbox{\rm sg} } } }$$

In examples throughout this thesis I will often abbreviate the semantic structures presented above (somewhat informally for expository purposes) as follows. Semantic structures of which the sort attribute is ` nullary' are abbreviated by Pred where Pred is the (atomic) value of the pred attribute. Semantic structures of type ` unary', ` binary', and ` ternary' are abbreviated resp. by Pred(Arg1), Pred(Arg1, Arg2) and Pred(Arg1, Arg2, Arg3) where Pred is the (atomic) value of the pred attribute and Arg1, Arg2 and Arg3 are resp. the (abbreviated) values of the arg1, arg2 and arg3 attributes. Semantic structures of sort ` modifier' are abbreviated as [Mod](Arg1) where Mod is the abbreviation of the value of the mod attribute, and Arg1 the abbreviation of the value of the arg1 attribute. Semantic structures of sort ` refer' are abbreviated by ref. Finally, for each of these abbreviations, if the value I of their corresponding index attribute occurs more than once in a structure, the abbreviated semantic structure is prefixed with I:. The values of other attributes will be abstracted away from in such abbreviated semantic structures.

As an example, I write the semantic structure corresponding to `The soldiers tried to shoot the very brave columbian minister' as

$$\mbox{\rm try($\mbox{\rm I}$:soldier,shoot($\mbox{\rm I}$:ref,[[very](brave)]([columbian](minister))))}$$