The Index Update Problem for XML Data in XDBMS

Database Management Systems are a major component of almost every information system. In relational Database Management Systems (RDBMS) indexes are well known and essential for the performant execution of frequent queries. For XML Database Management Systems (XDBMS) no index standards are established yet; although they are required not less. An inevitable side effect of any index is that modifications of the indexed data have to be reflected by the index structure itself. This leads to two problems: first it has to be determined whether a modifying operation affects an index or not. Second, if an index is affected, the index has to be updated efficiently best without rebuilding the whole index. In recent years a lot of approaches were introduced for indexing XML data in an XDBMS. All approaches lack more or less in the field of updates. In this paper we give an algorithm that is based on finite automaton theory and determines whether an XPath based database operation affects an index that is defined universally upon keys, qualifiers and a return value of an XPath expression. In addition, we give algorithms how we update our KeyX indexes efficiently if they are affected by a modification. The Index Update Problem is relevant for all applications that use a secondary XML data representation (e.g. indexes, caches, XML replication/synchronization services) where updates must be identified and realized.