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Projective Distribution of XQuery with Updates

机译:带有更新的XQuery的投影分布

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We investigate techniques to automatically decompose any XQuery queryȁ4;including updating queries specified by the XQuery Update Facility (XQUF)ȁ4;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 refined to a pass-by-projection semantics by means of a novel runtime XML projection technique, which safely eliminates most semantic differences between the local and remote execution of an XQuery expression, and strongly reduces message sizes. Finally, we discuss how these techniques can be used for updating queries, both under the standard W3C XQUF specification, as well as under an extended semantics that allows to update remote documents. The proposed techniques are implemented in XRPC, a simple yet efficient XQuery extension that enables function-shipping by adding a Remote Procedure Call mechanism to XQuery. Experiments on MonetDB/XQuery establish the performance potential of our XQuery decomposition techniques.
机译:我们研究了自动分解任何XQuery查询4的技术;包括将XQuery Update Facility(XQUF)4指定的查询更新为子查询,这些查询可以在其数据源附近执行,即函数装运。此处解决的主要挑战是,当XML节点(的一部分)通过网络发送并有效地进行复制时,要确保分解后的查询正确尊重XML节点身份并保留结构属性。我们从精确地描述条件开始,在此条件下,按值传递参数传递会导致XQuery表达式的远程执行与其本地执行之间的语义差异。然后,我们制定了一种保守策略,可以有效避免此类情况下的分解。为了拓宽查询分布的可能性,我们将按值传递语义扩展为按片段传递语义,这可以更好地跟踪节点标识和结构属性。随后,通过新颖的运行时XML投影技术,将按片段传递的语义提炼为按投影传递的语义,该技术可安全消除XQuery表达式的本地和远程执行之间的大多数语义差异,并极大地减小了消息大小。最后,我们讨论如何在标准W3C XQUF规范下以及在允许更新远程文档的扩展语义下,将这些技术用于更新查询。所提出的技术在XRPC中实现,XRPC是一种简单而有效的XQuery扩展,它通过向XQuery添加远程过程调用机制来实现功能传递。 MonetDB / XQuery上的实验确定了XQuery分解技术的性能潜力。

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