Information Modeling and Relational Databases, 2nd Edition

3.5. CSDP Step 3: Trim Schema; Note Basic Derivations

Having drawn the fact types and performed a population check, we now move on to step 3 of our design procedure. Here we check to see if there are some entity types that should be combined. We also check to see if some fact types can be derived from the others by arithmetic computation.

CSDP step 3: Check for entity types that should be combined; note any arithmetic derivations

To understand the first part of this step, we need to know how the objects in the UoD are classified into types. Figure 3.22 shows the basic division of objects into entities (non-lexical objects) and values (lexical objects). Entities are identified by definite descriptions and may typically change their state, whereas ...