There are many systems proposed for XML query evaluation, and even more for text queries, that have quite ad hoc definitions and empiricially specified behaviors. In contrast, the bedrock for relational database systems has been a very well-specified algebra that has provided a valuable intellectual basis and a useful framework for query optimization. This paper represents a strong attempt at establishing an algebraic basis for querying text in XML.

Whether the proposed algebra will suffice, it is too early to tell. I myself (along with my co-authors) had proposed the TIX algebra [citation 1 in the bibliography of this paper] some years ago to address precisely this need. The current paper significantly extends that proposal, and is thus more likely to capture enough of the nuances of queries over text data.