Journal of Theoretical and Applied Information Technology
In the past, to answer a user query, the authors generally extract data from one centralized database or from multiple sources with the same structure. Then things have been changed and they are facing the fact that in some cases, it is necessary to use a set of data sources to provide a complete information. These sources are physically separated, but they are logically seen as a single component to the final user. Besides the structure heterogeneity, there is another important point for what specialists are trying to find a solution which is the semantic heterogeneity of data sources.