Abstract not found

Keywords. Data exchange, XML, Relational databases, XML Queries. XML is the standard format for data exchange between inter-enterprise applications on the Internet. To facilitate data exchange, industry groups dene public document type denitions (DTDs) that specify the format of the XML data to be exchanged between their applications. In this paper, we address the problem of automating the conversion of relational data into XML. We describe SilkRoute, a general, dynamic, and ecient tool for viewing and querying relational data in XML. SilkRoute is general, because it can express mappings of relational data into XML that conforms to arbitrary DTDs, not just a canonical mapping of the relational schema. We call these mappings views. Applications express the data they need as an XML-QL query over the view. SilkRoute is dynamic, because it only materializes the fragment of an XML view needed by an application, and it is ecient, because it fully exploits the underlying RDBMs que...

This paper presents structural recursion as the basis of the syntax and semantics of query languages for semistructured data and XML. We describe a simple and powerful query language based on pattern matching and show that it can be expressed using structural recursion, which is introduced as a top-down, recursive function, similar to the way XSL is defined on XML trees. On cyclic data, structural recursion can be defined in two equivalent ways: as a recursive function which evaluates the data top-down and remembers all its calls to avoid infinite loops, or as a bulk evaluation which processes the entire data in parallel using only traditional relational algebra operators. The latter makes it possible for optimization techniques in relational queries to be applied to structural recursion. We show that the composition of two structural recursion queries can be expressed as a single such query, and this is used as the basis of an optimization method for mediator systems. Several other fo...

XML is becoming the most relevant new standard for data representation and exchange on the WWW. Novel languages for extracting and restructuring the XML contenthave been proposed, some in the tradition of database query languages #i.e. SQL, OQL#, others more closely inspired by XML. No standard for XML query language has yet been decided, but the discussion is ongoing within the World Wide Web Consortium and within many academic institutions and Internet-related major companies. We present a comparison of #ve, representative query languages for XML, highlighting their common features and di#erences. 1 Introduction to the #ve languages 1.1 LOREL LOREL was originally designed for querying semistructured data and has now been extended to XML data; it was conceived and implemented at Stanford University #S. Abiteboul, D. Quass, J. McHugh, J. Widom, J. Wiener# and its prototype is at http:##www-db.stanford.edu#lore. It is a user-friendly language in the SQLnOQL style, it includes a...

Abstract. An increasing number of distributed applications will be written for mobile hosts, such as laptop computers, third generation mobile phones, personal digital assistants, watches and the like. Application engineers have to deal with a new set of problems caused by mobility, such as low bandwidth, context changes or loss of connectivity. During disconnection, users will typically update local replicas of shared data independently from each other. The resulting inconsistent replicas need to be reconciled upon re-connection. To support building mobile applications that use both replication and reconciliation over ad-hoc networks, we have designed xmiddle, a mobile computing middleware. In this paper we describe xmiddle and show how it uses reflection capabilities to allow application engineers to influence replication and reconciliation techniques. xmiddle enables the transparent sharing of XML documents across heterogeneous mobile hosts, allowing on-line and off-line access to data. We describe xmiddle using a collaborative e-shopping case study on mobile clients.

XML documents are typically queried with a combination of value search and structure search. While querying by values can leverage traditional database technologies, evaluating structural relationship, specifically parent-child or ancestor-descendant relationship, between XML element sets has imposed a great challenge on efficient XML query processing. This paper proposes XR-tree, namely, XML Region Tree, which is a dynamic external memory index structure specially designed for strictly nested XML data. The unique feature of XR-tree is that, for a given element, all its ancestors (or descendants) in an element set indexed by an XRtree can be identified with optimal worst case I/O cost. We then propose a new structural join algorithm that can evaluate the structural relationship between two XR-tree indexed element sets by effectively skipping ancestors and descendants that do not participate in the join. Our extensive performance study shows that the XR-tree based join algorithm significantly outperforms previous algorithms. 1.

In this paper, we argue that middleware for wired distributed systems cannot be used in a mobile setting, as the principle of transparency that has driven their design runs counter to the new degrees of awareness imposed by mobility. We propose the marriage of reflection and metadata as a means for middleware to give applications dynamic access to information about their execution context. Finally, we describe a conceptual model that provides the basis of our reflective middleware.

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XML queries are usually expressed by means of XPath expressions identifying portions of the selected documents. An XPath expression defines a way of navigating an XML tree and returns the set of nodes which are reachable from one or more starting nodes through the paths specified by the expression. The problem of efficiently answering XPath queries is very interesting and has recently received increasing attention by the research community. In particular, an increasing effort has been devoted to define effective optimization techniques for XPath queries. One of the main issues related to the optimization of XPath queries is their minimization. The minimization of XPath queries has been studied for limited fragments of XPath, containing only the descendent, the child and the branch operators. In this work, we address the problem of minimizing XPath queries for a more general fragment, containing also the wildcard operator. We characterize the complexity of the minimization of XPath queries, stating that it is NP-hard, and propose an algorithm for computing minimum XPath queries. Moreover, we identify an interesting tractable case and propose an ad hoc algorithm handling the minimization of this kind of queries in polynomial time.

Recent advances in wireless networking technologies and the growing success of mobile computing devices, such as laptop computers, third generation mobile phones, personal digital assistants, watches and the like, are enabling new classes of applications that present challenging problems to designers. Mobile devices face temporary loss of network connectivity when they move; they are likely to have scarce resources, such as low battery power, slow CPU speed and little memory; they are required to react to frequent and unannounced changes in the environment, such as high variability of network bandwidth, and in the resources availability. To support designers building mobile applications, research in the field of middleware systems has proliferated. Middleware aims at facilitating communication and coordination of distributed components, concealing complexity raised by mobility from application engineers as much as possible. In this survey, we examine characteristics of mobile distributed systems and distinguish them from their fixed counterpart.