Structural similarity search in trees

Any key words to search for in the literature?

I know of similarity between trees, but that does not appear to apply here. First of all, the query is likely to be much smaller than the documents, and therefore the similarity is likely to be low. Secondly, the query may specify things which can't be expressed as trees. For instance, suppose people search for nodes labeled A which have either a child labeled B or a grandchild labeled C. This disjunction cannot be expressed as a tree.

The second question is the relationship between the similarity and the relevance. How do we know that a similar tree is also more relevant to the user? It would be nice to have a theoretical foundation for this.

kai

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