The design of a query language for XML data

XML data are expected to be widely used in Web information systems and EC/EDI applications. Such applications usually use a large number of XML data. First, we must allow users to retrieve only necessary portions of XML data by specifying search conditions to flexibly describe such applications. Second, we must allow users to combine XML data from different sources. To this end, we will provide a query language for XML data tentatively called XQL. We have designed XQL, keeping in mind its continuity with database standards such as SQL and OQL although we don't stick to its strict conformity. In this paper, we describe the requirements for a query language for XML data and explain the functionality of XQL including XML version of database operators such as select, joint, sort, grouping, union, and view definition. We make brief comments on the implementation and semantics.