XML Database Management Systems Research Articles

Pushing similarity joins down to the storage layer in XML databases

PurposeThis article aims to explore how to incorporate similarity joins into XML database management systems (XDBMSs). The authors aim to provide seamless and efficient integration of similarity joins on tree-structured data into an XDBMS architecture.Design/methodology/approachThe authors exploit XDBMS-specific features to efficiently generate XML tree representations for similarity matching. In particular, the authors push down a large part of the structural similarity evaluation close to the storage layer.FindingsEmpirical experiments were conducted to measure and compare accuracy, performance and scalability of the tree similarity join using different similarity functions and on the top of different storage models. The results show that the authors’ proposal delivers performance and scalability without hurting the accuracy.Originality/valueSimilarity join is a fundamental operation for data integration. Unfortunately, none of the XDBMS architectures proposed so far provides an efficient support for this operation. Evaluating similarity joins on XML is challenging, because it requires similarity matching on the text and structure. In this work, the authors integrate similarity joins into an XDBMS. To the best of the authors’ knowledge, this work is the first to leverage the storage scheme of an XDBMS to support XML similarity join processing.

A Dynamic Labeling Scheme Based on Logical Operators: A Support for Order-Sensitive XML Updates

Abstract Dynamic XML labeling schemes have demonstrated important usages in XML Database Management Systems. Several researches have been conducted to provide dynamic labeling schemes that can efficiently process queries with less label size and space overhead in addition to the capability of processing order-sensitive updates effectively and efficiently (i.e., without re-labeling). In this paper, we introduce a dynamic labeling scheme as an enhancement to our previous static one, XDAS. Dynamic XDAS is developed as a hybrid labeling scheme that combines the original XDAS with another labeling scheme called IBSL. Dynamic XDAS conveys all characteristics of the original XDAS in addition to the efficient treatment with update processes with no re-labeling, which is adapted from IBSL. Like the original XDAS, our experiments show that dynamic XDAS still can identify the A-D, P-C and sibling relationships using logical operators with efficient label size and storage space. Moreover, dynamic XDAS is capable for processing node/subtree updates efficiently with completely avoiding re-labeling or re-calculations, just like IBSL.

An active rule-based fuzzy XML database system

XML databases have been widely used for web applications to facility data exchanges through internet. Traditional database systems, including XML systems, usually handle precise and well-defined data. In the real world, there exist data that is uncertain and ambiguous. Fuzzy logic reflects human nature to express and evaluate the world in a vague manner. This paper describes our approach of incorporating fuzzy logic into XML database systems. Our system is built on top of an existing XML database management system, which allows the definition and storage of fuzzy data in addition to crisp information. We defined a query language based on the XQuery standard that allows users to query the underlying database using fuzzy expressions. Another important issue in a database system is integrity constraint management. Active rules, also named Event-Condition-Active rules, have mainly been used in relational database systems for integrity control, which are promising features for XML databases. Our fuzzy system includes an active rule-based subsystem that supports the specification and execution of active rules. Users can use fuzzy expressions in the rule definition to declaratively define business logic. The system supports different types of events, including temporal events and composite events, in addition to traditional mutation events.

XML indexing and storage: fulfilling the wish list

XML Indexing and Storage (XMIS) techniques are crucial for the functionality and the overall performance of an XML database management system (XDBMS). Because of the complexity of XQuery and performance demands of XML query processing, efficient path processing operators--including those for tree-pattern queries (so-called twigs)--are urgently needed for which tailor-made indexes and their flexible use are indispensable. Although XML indexing and storage are standard problems and, of course, manifold approaches have been proposed in the last decade, adaptive and broad-enough solutions for satisfactory query evaluation support of all path processing operators are missing in the XDBMS context. Therefore, we think that it is worthwhile to take a step back and look at the complete picture to derive a salient and holistic solution. To do so, we first compile an XMIS wish list containing what--in our opinion--are essential functional storage and indexing requirements in a modern XDBMS. With these desiderata in mind, we then develop a new XMIS scheme, which--by reconsidering previous work--can be seen as a practical and general approach to XML storage and indexing. Interestingly, by working on both problems at the same time, we can make the storage and index managers live in a kind of symbiotic partnership, because the document store re-uses ideas originally proposed by the indexing community and vice versa. The XMIS scheme is implemented in XTC, an XDBMS used for empirical tests.

Labeling Dynamic XML Documents: An Order-Centric Approach

Dynamic XML labeling schemes have important applications in XML Database Management Systems. In this paper, we explore dynamic XML labeling schemes from a novel order-centric perspective. We compare the various labeling schemes proposed in the literature with a special focus on their orders of labels. We show that the order of labels fundamentally impacts the update performance of a labeling scheme and develop an order-based framework to classify and characterize XML labeling schemes. Although there are dynamic XML labeling schemes that can completely avoid relabeling, the gain in update performance all come with considerable costs such as larger label size and lower query performance, even if the XML documents are hardly updated. We introduce vector order which is the foundation of the dynamic labeling schemes we propose. Compared with previous solutions that are based on natural order or lexicographical order, vector order is a simple, yet most effective solution to process updates in XML DBMS. We show that vector order can be gracefully applied to both range-based and prefix-based labeling schemes with little overhead introduced. Moreover, vector order-based labeling schemes are not only efficient to process, but also resilient to skewed insertions. Qualitative and experimental evaluations confirm the benefits of our approach compared to previous solutions.

Storing XML Data – The ExDB and CellStore Way in the Context of Current Approaches

In this paper we describe possible approaches how to store XML data, which is a key aspect for their further processing. One popular technique for managing XML data is to map the data to an existing database system, e.g., to the relational or object-relational database management system. We describe possible ways how to store XML data in relational databases, because relational systems are still widely used for various purposes, including XML data management. But XML data are trees, not tables, so the main focus of this article is oriented to native XML databases. We describe general properties of such kind of databases and, in particular, explain possible solutions on two experimental native XML database management systems – ExDB and CellStore. Both have been proposed, implemented and optimized in our research groups in recent years for experimental purposes.

An Efficient XML Index for Keyword Query with Semantic Path in Database

With the wide adoption of XML in many applications, people begin to manage thousands of XML documents in database. In many applications which backend data source powered by a XML database management system, k eyword search is important to query XML data with a regular structure if the user does not know the structure or only knows the structure partially. Essentially, many keyword search can be rewritten to XPath query Q = [//|/] e 1 [//|/] e 2 [//|/] … [//|/] e m [ text() =str ] -suppose there is a keyword search [ books William ] on XML data about publishing, the result could be the union of the results of the two queries after database system rewriting based on meta data: // books // chapters // authors [ text()=”William” ] and // books // authors [ text()=”William” ]. We propose an XML index structure BTP-Index, composed of XML structure index mechanism which backbone is a Suffix tree, for evaluation of path ([//|/] e 1 [//|/] e 2 [//|/]…[//|/] e m ) of Q , and XML content index mechanism which is based on Tries & Patricia tree, for the evaluation of [ text() = str ], filtering part of query Q. Using BTP-Index, we can process query Q efficiently . We have proven the effectiveness of BTP index in our Relation-XML dual engine database management system.

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.

Storing and querying XML data using denormalized relational databases

XML database systems emerge as a result of the acceptance of the XML data model. Recent works have followed the promising approach of building XML database management systems on underlying RDBMS’s. Achieving query processing performance reduces to two questions: (i) How should the XML data be decomposed into data that are stored in the RDBMS? (ii) How should the XML query be translated into an efficient plan that sends one or more SQL queries to the underlying RDBMS and combines the data into the XML result? We provide a formal framework for XML Schema-driven decompositions, which encompasses the decompositions proposed in prior work and extends them with decompositions that employ denormalized tables and binary-coded XML fragments. We provide corresponding query processing algorithms that translate the XML query conditions into conditions on the relational tables and assemble the decomposed data into the XML query result. Our key performance focus is the response time for delivering the first results of a query. The most effective of the described decompositions have been implemented in XCacheDB, an XML DBMS built on top of a commercial RDBMS, which serves as our experimental basis. We present experiments and analysis that point to a class of decompositions, called inlined decompositions, that improve query performance for full results and first results, without significant increase in the size of the database.

The carbohydrate sequence markup language (CabosML): an XML description of carbohydrate structures

Bioinformatics resources for glycomics are very poor as compared with those for genomics and proteomics. The complexity of carbohydrate sequences makes it difficult to define a common language to represent them, and the development of bioinformatics tools for glycomics has not progressed. In this study, we developed a carbohydrate sequence markup language (CabosML), an XML description of carbohydrate structures. The language definition (XML Schema) and an experimental database of carbohydrate structures using an XML database management system are available at http://www.phoenix.hydra.mki.co.jp/CabosDemo.html kikuchi@hydra.mki.co.jp.