Towards non-directional Xpath evaluation in a RDBMS

XML query languages use directional path expressions to locate data in an XML data collection. They are tightly coupled to the structure of a data collection, and can fail when evaluated on the same data in a different structure. This paper extends path ex-pressions with a new non-directional axis called the rank-distance axis. Given a context node and two positive integers α and β, the rank-distance axis returns those nodes that are ranked between α and β in terms of closeness from the context node in any direc-tion. This paper shows how to evaluate the rank-distance axis in a tree-unaware XML database. A tree-unaware implementation does not invade the database kernel to support XML queries, in-stead it uses an existing RDBMS such as Microsoft’s SQL server as a back-end and provides a front-end layer to translate XML queries to SQL. This paper presents an overview of an algorithm that trans-lates queries with a rank-distance axis to SQL