Don’t Scrap It, Wrap It! A Wrapper Architecture for Legacy Data Sources (1997) by Mary Tork Roth isn’t the latest word on wrappers but is well written. (longer version, A Wrapper Architecture for Legacy Data Sources (1997) )
The wrapper idea is a good one, although Roth uses it in the context of a unified schema, which is then queried. With a topic map, you could query on the basis of any of the underlying schemas and get the data from all the underlying data sources.
That result is possible because a topic map has one representative for a subject and can have any number of sources for information about that single subject.
I haven’t done a user survey but suspect most users would prefer to search for/access data using familiar schemas rather than new “unified” schemas.