Unlocking Keys for XML Trees
نویسندگان
چکیده
We review key constraints in the context of XML as introduced by Buneman et al. We show that one of the proposed inference rules is not sound in general, and the axiomatisation proposed for XML keys is incomplete even if key paths are simple. Therefore, the axiomatisation and also the implication problem for XML keys are still unsolved. We propose a set of inference rules that is indeed sound and complete for the implication of XML keys with simple key paths. Our completeness proof enables us to characterise the implication of XML keys in terms of the reachability problem of nodes in a digraph. This results in a quadratic time algorithm for deciding XML key implication, and shows that reasoning for XML keys is practically efficient.
منابع مشابه
Keys with Upward Wildcards for
The paper proposes a key constraint language for XML and investigates its associated decision problems. The language is deened in terms of regular path expressions extended with downward and upward wildcards, which can not only move down XML document trees, but also upwards as well. In a uniform syntax it is capable of expressing both absolute keys and relative keys, which are important for hie...
متن کاملS(b)-Trees: An Optimal Balancing of Variable Length Keys
The paper studies the problem of maintaining external dynamic dictionaries with variable length keys. We introduce a new type of balanced trees, called S(b)-trees, which generalize traditional B-trees. Contrary to B-trees S(b)-trees provide optimal utilization of keys of variable length, while the data access time remains logarithmical, the same as for B-trees. The main property of the new tree...
متن کاملPromoting the Semantic Capability of XML Keys
Keys for XML data trees can uniquely identify nodes based on the data values on some of their subnodes, either in the entire tree or relatively to some selected subtrees. Such keys have an impact on several XML applications. A challenge is to identify expressive classes of keys with good computational properties. In this paper, we propose such a new class of keys. In comparison to previous work...
متن کاملStatic Analysis and Query Answering for Incomplete Data Trees with Constraints
Data trees serve as an abstraction of XML documents: in such trees, every node comes with a label from a finite alphabet, as well as a data value from an infinite set. Incomplete data trees model XML documents with incomplete information; they may include both structural incompleteness and incompleteness of data. Here we study two basic problems for incomplete data trees under typical constrain...
متن کاملFull-Text and Structural XML Indexing on B+-Tree
XML query processing is one of the most active areas of database research. Although the main focus of past research has been the processing of structural XML queries, there are growing demands for a full-text search for XML documents. In this paper, we propose XICS (XML Indices for Content and Structural search), novel indices built on a B-tree, for the fast processing of queries that involve s...
متن کامل