3. The method as claimed in claim 1 wherein each concept of the first graph represents a category of data that exists according to the first source schema.
3. The method as claimed in claim 1 wherein each concept of the first graph represents a category of data that exists according to the first source schema. 4. The method as claimed in claim 3 wherein each concept of the second graph represents a category of data that exists according to the second source schema, and wherein each concept of the first and second graph is a relation name with an associated set of attributes.