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Node names, variable instantiation, and matches

We will use the terms (lhs, rhs and inp) as introduced above to refer to the parts of a generic metarule being applied to an input tree. The nodes at lhs can take three different forms: a constant node, a typed variable node, and a non-typed variable node. The naming conventions for these different classes of nodes is given below. During the process of matching, variables are associated (we use the term instantiated) with `tree material'. According to its class a variable can be instantiated with different kinds of tree material: We define a match to be a complete instantiation of all variables appearing in the metarule. In the process of matching, there may be several possible ways of instantiating the set of variables of the metarule, i.e., several possible matches. This is due to the presence of non-typed variables. Now, we are ready to define what we mean by a successful matching. The process of matching is successful if the number of possible matches is greater then 0. When there is no possible match the process is said to fail. In addition to return success or failure, the process also return the set of all possible matches, which will be used for generating the output.
next up previous contents
Next: Structural Matching Up: The definition of a Previous: The definition of a
XTAG Project
1998-09-14