Lecture 28: Discrimination Trees

In path indexing, a term is stored via the set of paths from the root to the leaves. In discrimination tree indexing, a term is stored via a single path representing a fixed-order traversal of the term. Discrimination trees provide faster lookup for many operations and in particular when looking for database terms which can be instantiated to the query term (which is relevant for subsumption). On the other hand, finding terms unifiable with a query term is more complicated since we need to skip and identify subterms in the index.

Reading

• A draft chapter in the Handbook of Automated Reasoning on Term Indexing by I.V. Ramakrishnan, R. Sekar, A. Voronkov, pp. 42-48.
• Slides used in class.
• Code directory with a rudimentary implementation of path indexing (also available as gzipped tar file). The file disc.sml contains an implementation of discrimination trees.

Key Concepts

• Discrimination trees
• Skip lists

Links

• Previous lecture: Path Indexing
• Next lecture: Equality