6
General Schema Manipulation Operators
In the last chapter, we saw techniques for taking two schemas and finding matches and mappings between them. Mappings and matches are directly useful for translating data from one schema to another, which is the focus of a good deal of this book. However, we may wish to do more with schemas than simply map data from one to the other. For instance, it may be useful to take two schemas and create a single merged schema that can represent all of their data. We may wish to translate a schema from one data model to another (e.g., relational to XML). Given three schemas A,B, and C and mappings 
and , we may wish ...
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