chapter  9
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Unfolding and folding

Computing the perfect model for a deductive database consists of populating the IDB relations starting with the EDB and iterating until a fixed point is reached. Following the definitions in Chapter 2, the EDB relations are normally update types, and at least some of the IDB relations are query types. It is frequently the case that some of the IDB relations are neither update nor query types. We called these intermediate types .