Nicola Onose

ASTERIX: towards a scalable, semistructured data platform for evolving-world models

ASTERIX is a new data-intensive storage and computing platform project spanning UC Irvine, UC Riverside, and UC San Diego. In this paper we provide an overview of the ASTERIX project, starting with its main goal—the storage and analysis of data pertaining to evolving-world models. We describe the requirements and associated challenges, and explain how the project is addressing them. We provide a technical overview of ASTERIX, covering its architecture, its user model for data and queries, and its approach to scalable query processing and data management. ASTERIX utilizes a new scalable runtime computational platform called Hyracks that is also discussed at an overview level; we have recently made Hyracks available in open source for use by other interested parties. We also relate our work on ASTERIX to the current state of the art and describe the research challenges that we are currently tackling as well as those that lie ahead.

Rewriting nested XML queries using nested views

We present and analyze an algorithm for equivalent rewriting of XQuery queries using XQuery views, which is complete for a large class of XQueries featuring nested FLWR blocks, XML construction and join equalities by value and identity. These features pose significant challenges which lead to fundamental extension of prior work on the problems of rewriting conjunctive and tree pattern queries. Our solution exploits the Nested XML Tableaux (NEXT) notation which enables a logical foundation for specifying XQuery semantics. We present a tool which inputs XQuery queries and views and outputs an XQuery rewriting, thus being usable on top of any of the existing XQuery processing engines. Our experimental evaluation shows that the tool scales well for large numbers of views and complex queries.

XQuery at your web service

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.

Highly distributed XQuery with DXQ

Many modern applications, from Grid computing to RSS handling, need to support data processing in a distributed environment. Currently, most such applications are implemented using a general purpose programming language, which can be expensive to maintain, hard to configure and modify, and require hand optimization of the distributed data processing operations. We present Distributed XQuery (DXQ), a simple, yet powerful, extension of XQuery to support distributed applications. This extension includes the ability to deploy networks of XQuery servers, to remotely invoke XQuery programs on those servers, and to ship code between servers. Our demonstration presents two applications implemented in DXQ: the resolution algorithm of DNS, the Domain Name System, and the Narada overlay-network protocol. We show that our system can flexibly accommodate different patterns of distributed computation and present some simple but essential distributed optimizations.

DXQ: a distributed XQuery scripting language

We present DXQ, an extension of XQuery to support the effective and efficient development of distributed XML applications. A DXQ program can invoke remote DXQ programs both synchronously and asynchronously and can dynamically ship DXQ code to execute at remote servers. We illustrate the power of the language with two distributed applications: the resolution algorithm of the Domain Name System (DNS) and the Narada overlay-network protocol. Our implementation permits concurrent evaluation of DXQ expressions at each server and can produce results extensionally (as XML values) or intensionally (as DXQ expressions).

XML query optimization in the presence of side effects

The emergence of database languages with side effects, notably for XML, raises significant challenges for database compilers and optimizers. In this paper, we extend an algebra for the W3C XML query language with operations that allow data to be immediately updated. We study the impact of that extension on logical optimization, join detection, and pipelining. The main result of this work is to show that, with proper care, a number of important optimizations based on nested relational algebras remain applicable in the presence of side effects. Our approach relies on an analysis of the conditions that must be checked in order for algebraic rewritings to hold. An implementation and experimental results demonstrate the effectiveness of the approach.

Efficient rewriting of XPath queries using Query Set Specifications

We study the problem of querying XML data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of XPath queries. To compactly specify such families of queries we adopt the Query Set Specifications [14], a formalism close to context-free grammars. We say that query Q is expressible by the specification P if it is equivalent to some expansion of P. Q is supported by P if it has an equivalent rewriting using some finite set of Ps expansions. We study the complexity of expressibility and support and identify large classes of XPath queries for which there are efficient (PTIME) algorithms. Our study considers both the case in which the XML nodes in the results of the queries lose their original identity and the one in which the source exposes persistent node ids.

A better semantics for XQuery with side-effects

Formal semantics for XQuery with side-effects have been proposed in [13,16]. We propose a different semantics which is better suited for database compilation. We substantiate this claim by formalizing the compilation of XQuery extended with updates into a database algebra. We prove the correctness of the proposed compilation by mapping both the source language and the algebra to a common core language with list comprehensions and extensible tuples.

Querying data sources that export infinite sets of views

We study the problem of querying data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of queries. We revisit a classical setting in which the application queries are conjunctive queries and the source accepts families of conjunctive queries specified as the expansions of a (potentially recursive) Datalog program. We say that query Q is expressible by the program P if it is equivalent to some expansion of P. Q is supported by P if it has an equivalent rewriting using some finite set of Ps expansions. We present the first study of expressibility and support for sources that satisfy integrity constraints, which is generally the case in practice.

Yoo-Hoo!: building a presence service with XQuery and WSDL

XML is at the heart of Web services: It is used as the format for the messages exchanged between services and applications (using SOAP [7]), to describe the structure of those messages (using XML Schema [6, 8]), and to describe Web services interfaces (using WSDL [12]). Current approaches [5] to development of Web services hide the XML layer behind Java or C# APIs, preventing the application direct access to the original data and interface. The goal of the XButler project is to support fast and reliable development of Web services by enabling direct access to the XML data and Web-service interfaces. The main technical contribution of XButler is a binding between WSDL [12], the Web Services Description Language, and XQuery [14], the W3C XML query language. In particular, we extend XQuery with an import service statement, which provides transparent access to Web services from within an XQuery program. Conversely, XButler provides tool (called xquery2soap) which takes an XQuery module and deploys it as a SOAP service. The XButler toolset and the corresponding XQuery extensions are implemented on top of the Galax [2] XQuery processor. In our demonstration, we use XButler to deploy a userpresence service, called Yoo-Hoo!. Yoo-Hoo! integrates user-presence information from multiple service providers and can provide Yoo-Hoo! clients with information such as “the requested subscriber is on-line at Jabber” or “the subscriber’s cell phone is busy”. XButler dramatically simplifies the implementation and deployment of the Yoo-Hoo! service – the client and server can manipulate XML messages directly in XQuery and all low-level handling of SOAP messages is entirely transparent.