Inverted

An inverted Metamorph index is the most commonly used type of Metamorph index, and is created with CREATE METAMORPH INVERTED INDEX. In Texis version 7 (and compatibilityversion 7) and later, this is the default Metamorph index type created when no other flags are given, e.g. CREATE METAMORPH INDEX; in version 6 (or compatibilityversion 6), a compact index is created. The version 7 index option WORDPOSITIONS 'on' (here) also explicitly creates this type of Metamorph index (same effect as the INVERTED flag after METAMORPH).

An inverted Metamorph index maintains knowledge not only of what rows words occur in, but also what position in each row the words occur in (the WORDPOSITIONS). With such an index Texis can often avoid a post-search altogether, because the index contains all the information needed for phrase resolution and rank computation. This can speed up searches more than a compact Metamorph index, especially for ranking queries using LIKEP, or phrase searches. Because of the greater range of queries resolvable with an inverted Metamorph index (vs. compact), in Texis version 7 and later it is the default Metamorph type created. However, an inverted Metamorph index consumes more disk space, typically 20-30% of the text size versus about 7% for a compact Metamorph index. Index updating is also slower because of this.


Copyright © Thunderstone Software     Last updated: Jun 9 2017
Copyright © 2017 Thunderstone Software LLC. All rights reserved.