Context Of XML Research Articles

Benchmarking JSON Document Stores in Practice

The increasing dissemination of JSON as exchange and storage format through its popularity in business and analytical applications requires efficient storage and processing of JSON documents. Consequently, this led to the development of specialized JSON document stores and the extension of existing relational stores, while no JSON-specific benchmarks were available to assess these systems. In this work, we assess currently available JSON document store benchmarks and select the recently developed DeepBench benchmark to experimentally study important dimensions like analytical querying capabilities, object nesting and array unnesting. To make the computational complexity of array unnesting more tractable, we introduce an improvement that we evaluate within a commercial system as part of the common, performance-oriented development process in practice. We conclude our evaluation of well-known document stores with DeepBench and give new insights into strengths and potential weaknesses of those systems that were not found by existing, non-JSON benchmarking practices. In particular the algebraic optimization of JSON query processing is still limited despite prior work on hierarchical data models in the XML context.

A Survey to View Update Problem

Extensible markup language (XML) has become the de facto standard for representing and interchanging data in web-based applications. And XML view, a virtual window for specified users, has been widely applied. In practical systems, users encounter the so-called view update problem when they need update source data through the view. For a long time, the view update problem is an open question in database community. With the development of various data models, the corresponding view update problem has been widely researched. In this paper, we introduce the conception of view update problem. We survey and compare previous approaches. Especially, we emphasize the role of semantics. Focusing on the problem in XML context, we give a discussion and propose a framework, which collects the semantic information at view definition time. Some related techniques for implementing this framework are further introduced.

A Survey to View Update Problem

Extensible markup language (XML) has become the de facto standard for representing and interchanging data in web-based applications. And XML view, a virtual window for specified users, has been widely applied. In practical systems, users encounter the so-called view update problem when they need update source data through the view. For a long time, the view update problem is an open question in database community. With the development of various data models, the corresponding view update problem has been widely researched. In this paper, we introduce the conception of view update problem. We survey and compare previous approaches. Especially, we emphasize the role of semantics. Focusing on the problem in XML context, we give a discussion and propose a framework, which collects the semantic information at view definition time. Some related techniques for implementing this framework are further introduced.

Bidirectionalizing graph transformations

Bidirectional transformations provide a novel mechanism for synchronizing and maintaining the consistency of information between input and output. Despite many promising results on bidirectional transformations, these have been limited to the context of relational or XML (tree-like) databases. We challenge the problem of bidirectional transformations within the context of graphs, by proposing a formal definition of a well-behaved bidirectional semantics for UnCAL, i.e., a graph algebra for the known UnQL graph query language. The key to our successful formalization is full utilization of both the recursive and bulk semantics of structural recursion on graphs. We carefully refine the existing forward evaluation of structural recursion so that it can produce sufficient trace information for later backward evaluation. We use the trace information for backward evaluation to reflect in-place updates and deletions on the view to the source, and adopt the universal resolving algorithm for inverse computation and the narrowing technique to tackle the difficult problem with insertion. We prove our bidirectional evaluation is well-behaved. Our current implementation is available online and confirms the usefulness of our approach with nontrivial applications.

Reasoning about XML with temporal logics and automata

We show that problems arising in static analysis of XML specifications and transformations can be dealt with using techniques similar to those developed for static analysis of programs. Many properties of interest in the XML context are related to navigation, and can be formulated in temporal logics for trees. We choose a logic that admits a simple single-exponential translation into unranked tree automata, in the spirit of the classical LTL-to-Büchi automata translation. Automata arising from this translation have a number of additional properties; in particular, they are convenient for reasoning about unary node-selecting queries, which are important in the XML context. We give two applications of such reasoning: one deals with a classical XML problem of reasoning about navigation in the presence of schemas, and the other relates to verifying security properties of XML views.

Fragmenting very large XML data warehouses via K-means clustering algorithm

XML data sources are more and more gaining popularity in the context of a wide family of Business Intelligence (BI) and On-Line Analytical Processing (OLAP) applications, due to the amenities of XML in representing and managing semi-structured and complex multidimensional data. As a consequence, many XML data warehouse models have been proposed during past years in order to handle hetero-geneity and complexity of multidimensional data in a way traditional relational data warehouse approaches fail to achieve. However, XML-native database systems currently suffer from limited performance, both in terms of volumes of manageable data and query response time. Therefore , recent research efforts are focusing the attention on fragmentation techniques, which are able to overcome the limitations above. Derived horizontal fragmentation is already used in relational data warehouses, and can definitely be adapted to the XML context. However, classical fragmentation algorithms are not suitable to control the number of originated fragments, which instead plays a critical role in data warehouses, and, with more emphasis, distributed data warehouse architectures. Inspired by this research challenge, in this paper we propose the use of K-means clustering algorithm for effectively and efficiently supporting the fragmentation of very large XML data warehouses, and, at the same time, completely controlling and determining the number of originated fragments via adequately setting the parameter K. We complete our analytical contribution by means of a comprehensive experimental assessment where we compare the efficiency of our proposed XML data warehouse fragmentation technique against those of classical derived horizontal fragmentation algorithms adapted to XML data warehouses.

Information preserving XML schema embedding

A fundamental concern of data integration in an XML context is the ability to embed one or more source documents in a target document so that (a) the target document conforms to a target schema and (b) the information in the source documents is preserved . In this paper, information preservation for XML is formally studied, and the results of this study guide the definition of a novel notion of schema embedding between two XML DTD schemas represented as graphs. Schema embedding generalizes the conventional notion of graph similarity by allowing an edge in a source DTD schema to be mapped to a path in the target DTD. Instance-level embeddings can be derived from the schema embedding in a straightforward manner, such that conformance to a target schema and information preservation are guaranteed. We show that it is NP-complete to find an embedding between two DTD schemas. We also outline efficient heuristic algorithms to find candidate embeddings, which have proved effective by our experimental study. These yield the first systematic and effective approach to finding information preserving XML mappings.

Technical context and cultural consequences of XML

The Extensible Markup Language (XML) is an open standard for creating domain- and industry-specific markup vocabularies. XML has become the predominant mechanism for electronic data interchange between information systems and can be described as a universally applicable, durable “Code of Integration.” As we celebrate its tenth anniversary, it is appropriate to reflect on the role XML has played and the technical ecosystem in which it functions. In this paper, we discuss both the environment from which XML arose and its technical underpinnings, and we relate these topics to companion papers in this issue of the IBM Systems Journal. We discuss the broad consequences of XML and argue that XML will take its place among the technical standards having the greatest impact on the world in which we live. We conclude with some reflections on the significant technical, economic, and societal consequences that XML is likely to have in the future.

An information-theoretic approach to normal forms for relational and XML data

Normalization as a way of producing good relational database designs is a well-understood topic. However, the same problem of distinguishing well-designed databases from poorly designed ones arises in other data models, in particular, XML. While, in the relational world, the criteria for being well designed are usually very intuitive and clear to state, they become more obscure when one moves to more complex data models.Our goal is to provide a set of tools for testing when a condition on a database design, specified by a normal form , corresponds to a good design. We use techniques of information theory, and define a measure of information content of elements in a database with respect to a set of constraints. We first test this measure in the relational context, providing information-theoretic justification for familiar normal forms such as BCNF, 4NF, PJ/NF, 5NFR, DK/NF. We then show that the same measure applies in the XML context, which gives us a characterization of a recently introduced XML normal form called XNF. Finally, we look at information-theoretic criteria for justifying normalization algorithms.

Efficiently supporting order in XML query processing

XML is an ordered data model and XQuery expressions return results that have a well-defined order. However, little work on how order is supported in XML query processing has been done to date. In this paper we study the issues related to handling order in the XML context, namely challenges imposed by the XML data model, the variety of order requirements of the XQuery language, and the need to maintain order in the presence of updates to the XML data. We propose an efficient solution that addresses all these issues. Our solution is based on a key encoding for XML nodes that serves as node identity and at the same time encodes order. We design rules for encoding order of processed XML nodes based on the XML algebraic query execution model and the node key encoding. These rules do not require any actual sorting for intermediate results during execution. Our approach enables efficient order-sensitive incremental view maintenance as it makes most XML algebra operators distributive with respect to bag union. We prove the correctness of our order encoding approach. Our approach is implemented and integrated with Rainbow, an XML data management system developed at WPI. We have tested the efficiency of our approach using queries that have different order requirements. We have also measured the relative cost of different components related to our order solution in different types of queries. In general the overhead of maintaining order in our approach is very small relative to the query processing time.

Indexing in an XML context

Based on Cambridge University Press’s experiences, this paper provides an overview of the advantages and disadvantages of using XML to index books prior to typesetting.

TIMBER: A native XML database

This paper describes the overall design and architecture of the Timber XML database system currently being implemented at the University of Michigan. The system is based upon a bulk algebra for manipulating trees, and natively stores XML. New access methods have been developed to evaluate queries in the XML context, and new cost estimation and query optimization techniques have also been developed. We present performance numbers to support some of our design decisions. We believe that the key intellectual contribution of this system is a comprehensive set-at-a-time query processing ability in a native XML store, with all the standard components of relational query processing, including algebraic rewriting and a cost-based optimizer.

Active rules for XML: A new paradigm for E-services

XML is rapidly becoming one of the most widely adopted technologies for information exchange and representation. As the use of XML becomes more widespread, we foresee the development of active XML rules, i.e., rules explicitly designed for the management of XML information. In particular, we argue that active rules for XML offer a natural paradigm for the rapid development of innovative e-services. In the paper, we show how active rules can be specified in the context of XSLT, a pattern-based language for publishing XML documents (promoted by the W3C) which is receiving strong commercial support, and Lorel, a query language for XML documents that is quite popular in the research world. We demonstrate, through simple examples of active rules for XSLT and Lorel, that active rules can be effective for the implementation of e-commerce services. We also discuss the various issues that need to be considered in adapting the notion of relational triggers to the XML context.