Tag arrays

Abstract

The Burrows-Wheeler Transform (BWT) moves characters with similar contexts in a text together, where a character's context consists of the characters immediately following it. We say that a property has contextual locality if characters with similar contexts tend to have the same or similar values (``tags'') of that property. We argue that if we consider a repetitive text and such a property and the tags in their characters' BWT order, then the resulting string -- the text and property's {\em tag array} -- will be run-length compressible either directly or after some minor manipulation.