(Joint work with Irini Fundulaki).
In this project we deal with the specification, composition, and evaluation of
XML subtree queries.
Such queries can be used in defining views, either in data integration or in access control, an
d these views may as well be layered one on top of the other.
In applications such as data in
tegration and access control, an important task is to filter an input document to produce a
subdocument; that is, a document whose root-to-leaf paths is a
subset of the set of root-to-leaf paths of the original document and which inherits the
tree structure thereof. These are what we mean by subtree queries, and while they are
similar to XPath queries, they cannot be naturally specified either in
XPath, XQuery or in XSLT.
Attempting to represent subtree queries
in a general-purpose XML query language leads not only to cumbersome query
specifications but also to performance issues, since the query engine
cannot exploit the subtree nature of the query. The problem is exacerbated
when applications require the sequential composition of multiple
subtree queries, since it is even less likely that the composition can be recognized as a
subtree query and the evaluation be optimized accordingly.
We have implemented XSQLP (the XML Subtree Query Language Platform) that provides: