Integrating and querying information sources in the context of large-scale ontological knowledge

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Information abounds, and the introduction of commercially viable computer systems with mass storage to help manage information has prompted the development of database systems together with an underlying technology. By far the most successful are systems that are based on the relational data model. Such systems provide a clean conceptual domain specific interface to managed information. This shields application developers from the need to understand low level interfaces to existing data sources and their physical data organization and from the need to choose appropriate data structures and algorithms. Hence, for relational database systems, discovering efficient execution strategies, called plans, for data manipulation requests, called queries and updates, has been the focus of research for more than thirty years.