Projection
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Revision as of 11:14, 26 March 2010
Projection is the mechanism by which, in a given syntactic tree, one or two constituents are integrated into a more complex structure. It is the bottom-up movement of merging or collapsing one or two subordinate nodes into a higher node. In the UNLarium framework, projection is used to build the sentence structure out of the individual constituents (head, specifier, adjunct and complement) during natural language generation.
Syntax
Projection rules are S-rules of the replace type, i.e.:
<RELATION> := <RELATION>;
Where <RELATION> is a syntactic relation, including a <HEAD>, in case of head-only relations (VH, NH, PH, JH, AH, CH, IH, DH), or a <HEAD> and a <ARGUMENT>, in case of binary relations (VC, VS, VA, NC, NS, NA, etc.).
There are mainly two types of projection rules:
- Replace, when the number of relations in the left side is the same as in the right side, and which is used for collapsing single-branched structures (i.e., parent nodes that have one single child)
- Merge, when the number of relations in the left side is greater than in the right side, and which is used for collapsing double-branched structures (i.e., parent nodes that have two children).
Examples
- VH(%head):=VB(%head);
- The head of the verbal phrase becomes the head of the verbal intermediary projection (VB)
- VC(%head;%comp):=VB(%head;%comp);
- The head of the verbal phrase becomes the head of the verbal intermediary projection and the complement of the verbal phrase becomes the second argument of the verbl intermediary projection
- VB(%head;%comp)VA(%head;%adjt):=VB(VB(%head;%comp);%adjt);
- The verbal intermediary projection becomes the head of a higher intermediary projection that takes the adjunct to the verb as second argument
Observations
- Indexation
- As in S-rules, nodes in projection rules are always indexed, either by user-defined labels (such as %head, %comp or any other) or by the position in the left side of the rules.
- Sentence structure
- The main goal of projection rules is to build the sentence structure described in Syntax, i.e., to integrate all nodes into a single tree structure.
