Projective Distribution of XQuery with Updates

—We investigate techniques to automatically decompose any XQuery query—including updating queries specified by the XQuery Update Facility (XQUF)—into subqueries, that can be executed near their data sources, i.e., function-shipping. The main challenge addressed here is to ensure that the decomposed queries properly respect XML node identity and preserve structural properties, when (parts of) XML nodes are sent over the network, effectively copying them. We start by precisely characterizing the conditions, under which pass-by-value parameter passing causes semantic differences between remote execution of an XQuery expression and its local execution. We then formulate a conservative strategy that effectively avoids decomposition in such cases. To broaden the possibilities of query distribution, we extend the pass-by-value semantics to a pass-by-fragment semantics, which keeps better track of node identities and structural properties. The pass-by-fragment semantics is subsequently r...

• Type: Journal
• Year: 2010
• Where: TKDE
• Authors: Ying Zhang, Nan Tang, Peter A. Boncz
• Keywords: Semantics, TKDE 2010, XQuery, XQuery Expression