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.

The XML Stream Machine (XSM) system is a novel XQuery processing paradigm that is tuned to the efficient processing of sequentially accessed XML data (streams). The system compiles a given XQuery into an XSM, which is an XML stream transducer, i.e., an abstract device that takes as input one or more XML data streams and produces one or more output streams, potentially using internal buffers. We present a systematic way to translate XQueries into efficient XSMs: First the XQuery is translated into a network of XSMs that correspond to the basic operators of the XQuery language and exchange streams. The network is reduced to a single XSM by repeated application of an XSM composition operation that is optimized to reduce the number of tests and actions that the XSM performs as well as the number of intermediate buffers that it uses. Finally, the optimized XSM is compiled into a C program. First empirical results illustrate the performance benefits of the XSM-based processor.

. This document proposes an algebra for XML Query. The algebra has been submitted to the W3C XML Query Working Group. A novel feature of the algebra is the use of regular-expression types, similar in power to DTDs or XML Schemas, and closely related to Hasoya and Pierce's work on Xduce. The iteration construct is based on the notion of a monad, and involves novel typing rules not encountered elsewhere. 1 Introduction This document proposes an algebra for XML Query. This work builds on long standing traditions in the database community. In particular, we have been inspired by systems such as SQL, OQL, and nested relational algebra (NRA). We have also been inspired by systems such as Quilt, UnQL, XDuce, XML-QL, XPath, XQL, XSLT, and YATL. We give citations for all these systems below. In the database world, it is common to translate a query language into an algebra; this happens in SQL, OQL, and NRA, among others. The purpose of the algebra is twofold. First, the algebra is used to give...

This article studies the complexity of evaluating functional query languages for complex values such as monad algebra and the recursion-free fragment of XQuery. We show that monad algebra with equality restricted to atomic values is complete for the class TA[2O(n) , O(n)] of problems solvable in linear exponential time with a linear number of alternations. The monotone fragment of monad algebra with atomic value equality but without negation is complete for nondeterministic exponential time. For monad algebra with deep equality, we establish TA[2O(n) , O(n)] lower and exponential-space upper bounds. We also study a fragment of XQuery, Core XQuery, that seems to incorporate all the features of a query language on complex values that are traditionally deemed essential. A close connection between monad algebra on lists and Core XQuery (with “child ” as the only axis) is exhibited, and it is shown that these languages are expressively equivalent up to representation issues. We show that Core XQuery is just as hard as monad algebra w.r.t. query and combined complexity, and that it is in TC0 if the query is assumed fixed. As Core XQuery is NEXPTIME-hard, it is commonly believed that any algorithm for evaluating Core XQuery has to require exponential amounts of working memory and doubly exponential time in the worst case. We present a property of queries – the lack of a certain form of composition – that virtually all real-world XQueries have and that allows for query evaluation in singly exponential time and polynomial space. Still, we are able to show for an important special case – Core XQuery with equality testing restricted to atomic values – that the composition-free language is just as expressive as the language with composition. Thus, under widely-held complexitytheoretic assumptions, the composition-free language is an exponentially less succinct version of the language with composition.

Even though XML was rst introduced as a schema-less, self-describing data representation

Abstract. In this article we investigate a novel execution paradigm—ML-like pattern-matching— for XML query processing. We show that such a paradigm is well adapted for a common and frequent set of queries and advocate that it constitutes a candidate for efficient execution of XML queries far better than the current XPath-based query mechanisms. We support our claim by comparing performances of XPath-based queries with pattern based ones, and by comparing the latter with the two efficiency-best XQuery processor we are aware of. 1 Introduction, Motivations

We are addressing the ecient processing of continuous XML streams, in which the server broadcasts XML data to multiple clients concurrently through a multicast data stream, while each client is fully responsible for processing the stream.

We present a visual language for querying and transforming XML data. The language is based on a visual document metaphor and the notion of document patterns and rules. It combines a dynamic form-based interface for defining queries and transformation rules with powerful pattern matching capabilities and offers thus a highly expressive visual language. The design of the visual language is specifically targeted at end users.

Abstract. We provide a formal definition of information flows in XML transformations and, more generally, in the presence of type driven computations and describe a sound technique to detect transformations that may leak private or confidential information. We also outline a general framework to check middleware located information flows. 1

The increased usage of mobile devices coupled with an unprecedented demand for information has pushed the scalability problem of pull-based data service to the focus.