Editing Rete algorithm (section)

=== Memory indexing ===
The Rete algorithm does not mandate any specific approach to indexing the working memory.   However, most modern production systems provide indexing mechanisms.   In some cases, only beta memories are indexed, whilst in others, indexing is used for both alpha and beta memories.   A good indexing strategy is a major factor in deciding the overall performance of a production system, especially when executing rule sets that result in highly combinatorial pattern matching (i.e., intensive use of beta join nodes), or, for some engines, when executing rules sets that perform a significant number of WME retractions during multiple match-resolve-act cycles.   Memories are often implemented using combinations of hash tables, and hash values are used to perform conditional joins on subsets of WME lists and WMEs, rather than on the entire contents of memories.   This, in turn, often significantly reduces the number of evaluations performed by the Rete network.