Analyzing Current Systems › Summary of Current Systems Analysis Guidelines › Guidelines for Implied Entity Types

Guidelines for Implied Entity Types

• An implied entity type corresponds to a key and a set of fields that are dependent on that key and nothing else.
• Define relationships between all key groups.
• Purchase Order has a one-to-many relationship with Purchase Order Item, but a relationship cannot always be defined with certainty. Supplier, for example, cannot be associated with any other entity type based solely on its key.
• Include every relationship.

The implied data model includes many relationships, some of which may be redundant. See the chapter "Building the Analysis Model" for a discussion of redundancy.

During comparison checking, determine which relationships to keep.

• Many-to-many relationships that have attributes are resolved by using associative entity types.
• An associative entity type must have for its key the identifiers of all implied entity types that it associates.
• Optionality of relationships is undefined.
• Duplicate attributes must be identifiers.