taDOM: A Tailored Synchronization Concept with Tunable Lock Granularity for the DOM API

Storing, querying, and updating XML documents in multi-user environments requires data processing guarded by a transactional context to assure the well-known ACID properties, particularly with regard to isolate concurrent transactions. In this paper, we introduce the taDOM tree, an extended data model which considers organization of both attribute nodes and node values in a new way and allows fine-grained lock acquisition for XML documents. For this reason, we design a tailored lock concept using a combination of node locks, navigation locks, and logical locks in order to synchronize concurrent accesses to XML documents via the DOM API. Our synchronization concept supports user-driven tunable lock granularity and lock escalation to reduce the frequency of lock requests both aiming at enhanced transaction throughput. Therefore, the taDOM tree and the related lock modes are adjusted to the specific properties of the DOM API.