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Data heterogeneity in XML retrieval activities can be tackled by giving users the possibility to obtain approximate answers to their queries. XPath query relaxation has been proposed as a mechanism to provide approximate answers in the case of positive XPath queries. Under this mechanism, the “satisfaction score” of an answer is defined by looking at how the query must be relaxed to produce that answer, and the user is provided with the best \(k\) answers according to their satisfaction score (top- \(k\) query answering). In this paper we investigate the problem of top- \(k\) query answering for XPath queries with negation. We tackle the challenging issues that need to be carefully considered when dealing with the approximation of negated conditions and propose an incremental top- \(k\) query answering technique based on query relaxation. Specifically, after defining a weighted query language and its semantics, we develop a general incremental query evaluation framework, which is flexible enough to support different evaluation strategies. The experimental assessment confirms the effectiveness of the whole framework. [ABSTRACT FROM AUTHOR]

Schemas are often used to constrain the content and structure of XML documents. They can be quite big and complex and, thus, difficult to be accessed manually. The ability to query a single schema, a collection of schemas or to retrieve schema components that meet certain structural constraints significantly eases schema management and is, thus, useful in many contexts. In this paper, we propose a query language, named XSPath, specifically tailored for XML schema that works on logical graph-based representations of schemas, on which it enables the navigation, and allows the selection of nodes. We also propose XPath/XQuery-based translations that can be exploited for the evaluation of XSPath queries. An extensive evaluation of the usability and efficiency of the proposed approach is finally presented within the (E\cal X up) system . [ABSTRACT FROM AUTHOR]

Caching stores the results of previously answered queries in order to answer succeeding queries faster by reusing these results. We propose two different approaches for using caches of XSLT transformed XML data in order to answer queries. The first approach checks whether or not a current query Q can be directly answered from the result of a previously answered query Qi stored in the cache. The new query is otherwise submitted to the source over the network, the answer of the query is determined, transmitted back to the client, and stored in the cache. The second approach determines only the intersection Q-Qi and integrates the result of Q-Qi into the previous results in the cache, which requires applying a numbering scheme for the output of the XSLT stylesheet. We show by experimental results that the second approach can significantly speed up the answering time in comparison to the first approach, but is not significantly slower in few worst cases than the second approach. [ABSTRACT FROM AUTHOR]

Streams are preferable over data stored in memory in contexts where data is too large or volatile, or a standard approach to data processing based on storing is too time or space consuming. Emerging applications such as publish-subscribe systems, data monitoring in sensor networks, financial and traffic monitoring, and routing of MPEG-7 call for querying streams. In many such applications, XML streams are arguably more appropriate than flat streams, for they convey (possibly unbounded) unranked ordered trees with labeled nodes. However, the flexibility enabled by XML streams in data modeling makes query evaluation different from traditional settings and challenging. This paper describes SPEX, a streamed and progressive evaluation of XML Path Language (XPath). SPEX compiles queries into networks of simple and independent transducers and processes XML streams with polynomial combined complexity. This makes SPEX especially suitable for implementation on devices with low memory and simple logic as used, for example, in mobile computing. [ABSTRACT FROM AUTHOR]