Schema Evolution publication categorizer

Database middleware systems integrate data from multiple sources.
To be effective, such systemsmust provide a unified, queryable schema, and must be able to transform data from different sources to conform to this schema when queries against the schema are issued. The power of their query engines and their ability to connect to several information sources makes them a natural base for doing
more complex transformations as well. In this paper, we look at database middleware systems as tranformation engines, and discuss when and how data is transformed to provide users with the information they need.