Xcerpt and XChange – Logic Programming Languages for Querying and Evolution on the Web
The Semantic Web is an endeavor aiming at enriching the existing Web with meta-data and data (and meta-data) processing so as to allow computer systems to actually reason with the data instead of merely rendering it. To this aim, it is necessary to be able to query and update data and meta-data. Existing Semantic Web query languages (like DQL) are special purpose, they are not capable of processing generic Web data. On the other hand, the language Xcerpt [1,2] presented in the poster is a general purpose language that can query any kind of XML data and at the same time, being based on logic programming, provides advanced reasoning capabilities. Likewise, the maintenance and evolution of data on the (Semantic) Web is necessary: the Web is a ”living organism” whose dynamic character requires languages for specifying its evolution. This requirement regards not only updating data from Web resources, but also the propagation of changes on the Web. These issues have not received much attention so far, existing update languages (e.g. XML-RL Update Language ) and reactive languages  for the Web offer the possibility to execute simple update operations and, moreover, important features needed for propagation of updates on the Web are still missing. The language XChange also presented in the poster builds upon the query language Xcerpt and provides advanced, Web-specific capabilities, such as propagation of changes on the Web (change) and event-based communications between Web sites (exchange).
KeywordsLogic Programming Query Language Query Term Connected Query Logic Programming Language
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