Michael Peter Haustein

Node labeling schemes for dynamic XML documents reconsidered

We explore suitable node labeling schemes used in collaborative XML DBMSs (XDBMSs, for short) supporting typical XML document processing interfaces. Such schemes have to provide holistic support for essential XDBMS processing steps for declarative as well as navigational query processing and, with the same importance, lock management. In this paper, we evaluate existing range-based and prefix-based labeling schemes, before we propose our own scheme based on DeweyIDs. We experimentally explore its suitability as a general and immutable node labeling mechanism, stress its synergetic potential for query processing and locking, and show how it can be implemented efficiently. Various compression and optimization measures deliver surprising space reductions, frequently reduce the size of storage representation-compared to an already space-efficient encoding scheme-to less than 20-30% in the average and, thus, conclude their practical relevance.

An efficient infrastructure for native transactional XML processing

Implementation techniques for relational database management systems (DBMSs) have proven their efficiency and robustness in many existing systems. However, many of these concepts and mechanisms cannot be used when implementing a native XML DBMS (XDBMS) because of substantial differences in the processing properties of natively stored XML documents as compared to relational tables. Therefore, we have to develop new and appropriate techniques with ACID transaction guarantees tailored to the processing characteristics of tree documents and the operations on them. For this reason, we want to provide for an efficient infrastructure of XDBMSs consisting of tree node addressing and indexing together with fine-grained locking of tree nodes. In this respect, our prime and novel contribution is to reveal the potential of our prefix-based node labeling called DeweyIDs supporting record addressing, indexing, and locking protocols. In this paper, we first sketch our version of prefix-based node labeling and summarize a quantitative study on them. An overview of our layered XDBMS architecture indicates the concepts and functionalities to be reused from relational DBMS implementations. The core part of the paper describes the infrastructural services for XML document storage with compressed DeweyIDs, the principles and methods for navigational and declarative processing of queries, as well as the lock modes and protocols to enable efficient collaboration. Selected empirical experiments evaluate the XTC system performance and support our system assessment.

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.

Adjustable Transaction Isolation in XML Database Management Systems

Processing XML documents in multi-user database management environments requires a suitable storage model of XML data, support of typical XML document processing (XDP) interfaces, and concurrency control (CC) mechanisms tailored to the XML data model. In this paper, we sketch the architecture and interfaces of our prototype native XML database management system which can be connected to any existing relational DBMS and provides for declarative and navigational data access of concurrent transactions. We describe the fine-grained CC mechanisms implemented in our system and give a first impression of the so achieved benefits for concurrent transaction processing in native XML database management systems.

Locking-aware structural join operators for XML query processing

As observed in many publications so far, the matching of twig pattern queries (i.e., queries that contain only the child and the descendant axis) is a core operation in XML database management systems (XDBMSs) for which the structural join and the holistic twig join algorithms were proposed. In a single-user environment, especially the latter algorithm provides a good evaluation strategy. However, when it comes to multi-user access to a single XML document, it may lead to extensive blocking situations: The XDBMS has to ensure data consistency and, therefore, has to prevent concurrent modification operations from changing elements in the input sequences, a holistic twig algorithm accesses while operating. To circumvent this problem, we propose a set of new locking-aware operators for twig pattern query evaluation that rely on stable path labels (SPLIDs) as well as document and element set indexes. Furthermore, by running extensive tests on our own XDBMS, we show that their performance is comparable to existing approaches in a single-user environment, and leads to higher throughput rates in the case of multi-user access.

Implementing and Optimizing Fine-Granular Lock Management for XML Document Trees

Fine-grained lock protocols with lock modes and lock granules adjusted to the various XML processing models, allow for highly concurrent transaction processing on XML trees, but require locking facilities that efficiently support large and deep hierarchies with varying fan-out characteristics. We discuss these and also further requirements like prefix-based node labels, and present a lock management design that fulfills all these requirements and allows us to perfectly exploit the advantages of our tailor-made lock protocols for XML trees. Our design also supports the flexible use of heuristics for dynamic lock escalation to enhance workload adaptivity. Benchmark runs convincingly illustrate flexibility and performance benefits of this approach and reveal that careful lock protocol optimization pays off.