Optimization challenges in EMERAC
Each relation is exported in to-to by a single database
All sources are assumed to be fully relational
Multiple sources export partial and overlapping portions of a relation
- Need to minimize plans to remove redundancy
Sources are rarely fully relational
- Only limited types of queries allowed
- Wrapped web-pages
- Form-interfaced databases
- Certain forms of join computation may be precluded
- Need to model query capabilities