XPlainer: Visual explanations of XPath queries

The popularity of XML has motivated the development of novel XML processing tools many of which embed the XPath language for XML querying, transformation, constraint specification, etc. XPath developers (as well as less technical users) have access to commercial tools to help them use the language effectively. Example tools include debuggers that return the result of XPath subexpressions visualized in the context of the input XML document. This paper introduces XPlainer, a language that provides explanations of why XPath expressions return a specific answer. An explanation returns precisely the nodes in the input XML document that contribute to the answer. We provide a complete formalization for explanation queries based on the semantics of XPath. This enables the use of XPath engines for the evaluation of explanation queries. We describe a tool that uses XPlainer queries to provide visual explanations. The XPlainer-Eclipse tool is built on an extensible development environment that includes editors for visualizing both XML documents and XPath expressions as trees together with the explanation of the answers.

Algebras for Querying Text Regions (Extended Abstract)

There is a significant amount of interest in combining and extending database and information retrieval technologies to manage textual data. The challenge is becoming more relevant due to the increased availability of documents in digital form. Document data has a natural hierarchical structure, which may be made explicit due to the use of markup conventions (as it is the case with SGML). An important aspect of managing structured and semi-structured textual data consists of supporting the efficient retrieval of text components based both on their content and structure. In this paper we study issues related to the expressive power and optimization of a class of algebras that support combining string (or pattern) searches with queries on the hierarch..