Tuesday, February 21, 14:00 in Celestijnenlaan 200S room 01.04
Representation and Query Answering of the Local Closed-World Assumption
By Alvaro Cortes Calabuig (DTAI)
One of the basic problems in the context of information integration systems over a number of independent data-sources is the representation of external knowledge about the data stored in each individual source. This meta-information is known as the local closed-world assumption (LCWA) of a data-source.
In this talk, we present an expressive and intuitively method of representing LCWA of autonomous data-sources. This approach distinguishes between the explicit data that is conveyed by a data-source and the implicit knowledge about the completeness of this data. The explicit data remains a set of facts, i.e., a relational database that can be queried in the standard way, whereas the implicit knowledge about its completeness is expressed by a first order theory that can be processed by an independent reasoning system (sometimes called the mediator). We consider different ways of representing our approach, relate it to other methods of representing local closed-world assumptions of data-sources, and show some useful properties of our framework which facilitate its application in real-life systems.