Lightweight multigranularity locking for transaction management in XML database systems

As eXtensible Markup Language (XML) provides a capability for describing data structures, and can accommodate many kinds of semistructured data. The semistructured data format is flexible for changing data structures through insertion and deletion of data elements in mission-critical applications. In the case of concurrently changing such a data format, this flexibility could be endangered by a phantom problem which might lead to inconsistent information flow. For the purpose of developing a concurrency control scheme without the phantom phenomenon, we propose a lightweight multigranularity locking (LWMGL) scheme that is a hybrid mechanism of Tree-based Locking and Multigranularity Locking. The goal of this scheme is to realize locking at the level of precise elements in an XML database while preventing the phantom problems. Since these precise locks could considerably reduce the number of pseudo-conflicts that are regarded as unnecessary locks, they provide high concurrency compared with other concurrency control schemes. In order to realize the LWMGL scheme we also devised a new data model of XML indexed element tables (XIETs) for transferring diverse XML documents. This data model does not only can preserve the XML tree structure in application levels, but also enables execution of the structural change operations as well as the data access operations in parallel.