Semantic Integration "Basically semantic integration seems to involve using RDF/OWL to define mappings between XML vocabularies.
Recently I've been involved in co-ordinating a number of large scale data migrations to help integrate several systems. This inevitably involved exploring the business models in the affected applications to define a mapping layer to allow the data to be cleanly migrated. Also inevitably this mapping ends up being expressed as a bunch of (hairy!) procedural code. It would have been nice to have been able to express that mapping in a more declarative way, if no other reason than it's easier to understand and debug possible problems. An example of not being able to see the wood for the trees."
There are many way to declaratively map different schemas - SQL, OO and XML all have their own tools. The value that RDF has is that you can program to a single ontology and map all of these different data sources to it.
With RDF there's not only the ability to map between XML vocabularies but to program to an ontology rather than a schema. In this case, the problem goes from MxN to M+N (or even just M).
One of the articles that highlights this issue is The Impedance Imperative Tuples + Objects + Infosets =Too Much Stuff!.