Abstract not found

XQuery is the de facto standard XML query language, and it is important to have efficient query evaluation techniques available for it. It is a well-known fact that a formal bulk algebra is essential for efficient query evaluation, and the Tree Algebra for XML (TAX), among others, is invented for this purpose. It can be shown in this thesis that a substantial subset of XQuery can be expressed as TAX. An XML document is often modelled as an ordered label tree. A core opera-tion in the evaluation of XQuery is the finding of matches for specified tree patterns against the data tree (or forest), and there has been much work towards algorithms for finding such matches efficiently. Multiple XPath expressions can be evaluated by computing one or more tree pattern matches. However, because of the flexibility of XML data, the efficient evaluation of XQuery queries as a whole is much more than a tree pattern match and combining matchings of multiple tree patterns is not the most efficient evaluation plan for XQuery. In this thesis a structure called generalized tree pattern (GTP) is proposed to concisely represent a whole XQuery expression. Evaluating a query reduces to finding the matches of its GTP, which leads to more efficient evaluation plans. Algorithms are developed to translate an XQuery expression, possibly involving join, quantifiers, grouping, aggregation and nesting, to its GTP, and to generate ii efficient physical plans for a specified GTP. XML data often conforms to a schema. Relevant constraints from the schema give rise to further opportunities to optimize queries. Algorithms are given in the thesis to automatically infer structural constraints from a given schema and to sim-plify a GTP given a set of structural constraints. Finally, a detailed set of experi-ments using the TIMBER XML database system shows that plans via GTPs (with or without schema knowledge) significantly outperform plans based on navigation and straightforward plans obtained directly from the query. iii

product, having over a million lines of Erlang code. This product (the AXD301) is thought to be one of the most reliable products ever made by Ericsson.

XML is the W3C standard document format for writing and exchanging information on the Web. RDF is the W3C standard model for describing the semantics and reasoning about information on the Web. Unfortunately, RDF and XML---although very close to each other---are based on two different paradigms. We argue that in order to lead the Semantic Web to its full potential, the syntax and the semantics of information needs to work together. To this end, we develop a model theory for the XML XQuery 1.0 and XPath 2.0 Data Model, which provides a unified model for both XML and RDF. This unified model can serve as the basis for Web applications that deal with both data and semantics. We illustrate the use of this model on a concrete information integration scenario. Our approach enables each side of the fence to benefit from the other, notably, we show how the RDF world can take advantage of XML query languages, and how the XML world can take advantage of the reasoning capabilities available for RDF.

XML messaging is at the heart of Web services, providing the flexibility required for their deployment, composition, and maintenance. Yet, current approaches to Web services development hide the messaging layer behind Java or C# APIs, preventing the application to get direct access to the underlying XML information. To address this problem, we advocate the use of a native XML language, namely XQuery, as an integral part of the Web services development infrastructure. The main contribution of the paper is a binding between WSDL, the Web Services Description Language, and XQuery. The approach enables the use of XQuery for both Web services deployment and composition. We present a simple command-line tool that can be used to automatically deploy a Web service from a given XQuery module, and extend the XQuery language itself with a statement for accessing one or more Web services. The binding provides tight-coupling between WSDL and XQuery, yielding additional benefits, notably: the ability to use WSDL as an interface language for XQuery, and the ability to perform static typing on XQuery programs that include Web service calls. Last but not least, the proposal requires only minimal changes to the existing infrastructure. We report on our experience implementing this approach in the Galax XQuery processor.

XQuery is a strongly typed, functional language, which supports the common processing, transformation, and querying tasks of a wide variety of XML applications. Following the tradition of other functional languages, XQuery includes a complete formal semantics. In this paper, we argue that basing an XQuery implementation on the XQuery Formal Semantics not only ensures correctness, but is a good foundation for optimization. We describe an architecture that we have implemented and that is based on the XQuery Formal Semantics and describe several logical and physical optimizations that can be easily integrated in the above architecture.

We distinguish between two broad categories of e-services: discrete services (e.g., add item to shopping cart, charge a credit card), and sessionoriented ones (teleconference, collaborative text chat, streaming video, ccommerce interactions). Discrete services typically have short duration, and cannot respond to external asynchronous events. Session-oriented services have longer duration (perhaps hours), and typically can respond to asynchronous events (e.g., the ability to add a new participant to a teleconference). When composing discrete e-services it usually suffices to use a process model and engine that composes the e-services as relatively independent tasks. But when composing session-oriented e-services, the engine must be able to receive asynchronous events and determine how and whether to impact the active sessions. For example, if a teleconference participant loses his wireless connection then it might be appropriate to trigger an announcement to some or all of the other participants. In this paper we propose a process model and architecture for flexible composition and execution of discrete and session-oriented services. Unlike previous approaches, our model permits the specification of scripted "active flowcharts" that can be triggered by asynchronous events, and can appropriately impact active sessions. We introduce here a model and language for specifying process schemas (essentially a collection of active flowcharts) that combine multiple e-services, and describe a prototype engine for executing these process schemas.

XML is the W3C standard document format for writing and exchanging information on the Web. RDF is the W3C standard model for describing the semantics and reasoning about information on the Web. Unfortunately, RDF and XML -- although very close to each other -- are based on two different paradigms. We argue that in order to lead the Semantic Web to its full potential, the syntax and the semantics of information need to work together. To this end, we develop a model theory for the XML XQuery 1.0 and XPath 2.0 Data Model, which provides a unified model for both XML and RDF. This unified model can serve as the basis for Web applications that deal with both data and semantics. We illustrate the use of this model on a concrete information integration scenario. Our approach enables each side of the fence to benefit from the other, notably, we show how the RDF world can take advantage of XML Schema description and XML query languages, and how the XML world can take advantage of the reasoning capabilities available for RDF. Our approach can also serve as a foundation for the next layer of the Semantic Web, the ontology layer, and we present a layering of an ontology language on top of our approach.

Methodologies for the engineering of Web applications typically provide models that drive the generation of the hypermedia navigation structure in the application. Most of these methodologies and their models consider link following as the only materialization of the navigation structure. In this paper we see how extended user input can dynamically influence the navigation structure. By means of Hera it is shown how one can define this extended user input and capture the functional aspects related to the hypermedia dynamics in the RDF(S)-based design models. For this purpose we discuss the definition of input controls, the representation of state information, and the embedding of both in the application model. We also present the XML/RDF-based architecture implementing this.

We present XML schemas and our design for related data services for describing faults and surface displacements, which we use within earthquake modeling codes. These data services are implemented using a Web services approach and are incorporated in a portal architecture with other, general purpose services for application and file management. We make use of many Web services standards, including WSDL and SOAP, with specific implementations in Java. We illustrate how these data models and services may be used to build distributed, interacting applications through data flow.