The World Wide Web promises to transform human society by making virtually all types of information instantly available everywhere. Two prerequisites for this promise to be realized are a universal markup language and a universal query language. The power and flexibility of XML make it the leading candidate for a universal markup language. XML provides a way to label information from diverse data sources including structured and semi-structured documents, relational databases, and object repositories. Several XML-based query languages have been proposed, each oriented toward a specific category of information. Quilt is a new proposal that attempts to unify concepts from several of these query languages, resulting in a new language that exploits the full versatility of XML. The name Quilt suggests both the way in which features from several languages were assembled to make a new query language, and the way in which Quilt queries can combine information from diverse data sou...

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...

Computing and telecommunications are maturing, and the next century promises a shift away from technology-driven general-purpose devices. Instead, we will focus on the needs of consumers: easy-to-use, low-maintenance, portable, ubiquitous, and ultra-reliable task-specific devices. Such devices, although not as limited by computational speed or communication bandwidth, will instead be constrained by new limits on size, form-factor, and power consumption. Data that they generate will need to be injected into the Internet and find its way to the services to which the user has subscribed. This is not simply a problem of ad-hoc networking, but one that requires re-thinking our basic assumptions regarding network transactions and challenges us to develop entirely new models for distributed services. Network topologies will be intermittent and services will have to be discovered independently of user guidance. In fact, data transfers from user interfaces to services and back, will need to become invisible to the user and guided by the task rather than explicit commands. This paper outlines a vision of this future and identifies research problems that will require our attention in the areas of user interfaces, distributed services, and networking infrastructure. 1

Abstract. This paper describes general storage and retrieval methods for XML documents using object-relational databases. The storage method decomposes tree structure of XML documents into nodes, and stores them in relational tables according to the node types. By using this method, being independent of DTDs or element types, any XML documents can be stored in databases. Also it is possible to utilize index structures(e.g. B + trees, R trees, etc.) which are provided in database management systems. As for retrieval, we show the transformation of XQL queries into SQL queries. It is possible to realize the storage method by doing minimal extension to object-relational databases and the retrieval method by adding a preprocessor of a query language. We also performed experiments using XML documents on the plays of Shakespeare, to show the effectiveness of our methods. 1

The rapid growth of the Web and the ease with which data can be accessed facilitate the distribution and sharing of information. Information dissemination often takes the form of documents that are made available at Web servers, or that are actively broadcasted byWeb servers to interested clients. In this paper, we present an XML-compliant formalism for specifying security-related information for Web document protection. In particular, we introduce X -Sec, an XML-based language for specifying subject credentials and security policies and for organizing them into subject profiles and policy bases, respectively. The language is complemented by a set of subscription-based schemes for accessing distributed Web documents, which rely on defined XML subject profiles and XML policy bases.

We present WSQ/DSQ (pronounced "wisk-disk"), a new approach for combining the query facilities of traditional databases with existing search engines on the Web. WSQ, for Web-Supported (Database) Queries, leverages results from Web searches to enhance SQL queries over a relational database. DSQ, for Database-Supported (Web) Queries, uses information stored in the database to enhance and explain Web searches. This paper focuses primarily on WSQ, describing a simple, low-overhead way to support WSQ in a relational DBMS, and demonstrating the utility of WSQ with a number of interesting queries and results. The queries supported by WSQ are enabled by two virtual tables, whose tuples represent Web search results generated dynamically during query execution. WSQ query execution may involve many high-latency calls to one or more search engines, during which the query processor is idle. We present a lightweight technique called asynchronous iteration that can be integrated easily into a standard sequential query processor to enable concurrency between query processing and multiple Web search requests. Asynchronous iteration has broader applications than WSQ alone, and it opens up many interesting query optimization issues. We have developed a prototype implementation of WSQ by extending a DBMS with virtual tables and asynchronous iteration; performance results are reported. 1

One of the most important issue in source code analysis and software re-engineering is the representation of source code text at an abstraction level and form suitable for algorithmic processing. Moreover, source code representation schemes must be compact, accessible by well defined application programming interfaces (APIs) and above all portable to different operating platforms and various CASE tools. This paper proposes a program representation technique that is based on language domain modes and the XML markup language. In this context, source code is represented as XML DOM trees that offer a higher level of openess and portability than custom-made tool specific Abstract Syntax Trees. The DOM trees can be exchanged between tools in textual or binary form. Similarly, the domain model allows for language entities to be associated with analysis services offered by various CASE tools, leading to an Integrated Software Maintenance Environment. 1

The World Wide Web Consortium recommends both XSLT and XQuery as query languages for XML documents. XSLT, originally designed to transform XML into HTML, is nowadays a fully grown XML query language that is mostly suited for use by machines. XQuery on the other hand was particularly designed to be easily used by humans. Since both query languages receive a steady growth in user acceptance, it is important and natural to ask about their expressive power. We show here that both XSLT and XQuery are Turing-complete by reduction to µ-recursive functions. Keywords: XML, XSLT, XQuery, Turing-completeness 1

There has been recent interest in using relational database systems to store and query XML documents. Each of the techniques proposed in this context works by (a) creating tables for the purpose of storing XML documents (also called relational schema generation), (b) storing XML documents by shredding them into rows in the created tables, and (c) converting queries over XML documents into SQL queries over the created tables. Since relational schema generation is a physical database design issue- dependent on factors such as the nature of the data, the query workload and availability of schemas- there have been many techniques proposed for this purpose. Currently, each relational schema generation technique requires its own query processor to efficiently convert queries over XML documents into SQL queries over the created tables. In this paper, we present an efficient technique whereby the same query-processor can be used for all such relational schema generation techniques. This greatly simplifies the task of relational schema generation by eliminating the need to write a special-purpose query processor for each new solution to the problem. In addition, our proposed technique enables users to query seamlessly across relational data and XML documents. This provides users with unified access to both relational and XML data without them having to deal with separate databases. 1.

Although originally designed for large-scale electronic publishing, XML plays an increasingly important role in the exchange of data on the Web. In fact, it is expected that XML will become the lingua franca of the Web, eventually replacing HTML. Not surprisingly, there has been a great deal of interest on XML both in industry and in academia. Nevertheless, to date no comprehensive study on the XML Web (i.e., the subset of the Web made of XML documents only) nor on its contents has been made. This paper is the first attempt at describing the XML Web and the documents contained in it. Our results are drawn from a sample of a repository of the publicly available XML documents on the Web, consisting of about 200,000 documents. Our results show that, despite its short history, XML already permeates the Web, both in terms of generic domains and geographically. Also, our results about the contents of the XML Web provide valuable input for the design of algorithms, tools and systems that use XML in one form or another.