ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE LOGICAL MODEL
• Relationship Type > Non-Identifying, Mandatory Relationships: Non-identifying relationships propagate the
parent's primary key to the non-key attributes of the child. A foreign key value must exist in the child entity and
the foreign key value must be found in the primary key of the parent.
The cardinality of a mandatory relationship must be in the form of one to something.
When generating a physical model, foreign key columns propagated by a mandatory relationship default to NOT
NULL.
• Relationship Type > Non-Specific Relationships: Non-specific relationships denote many-to-many
relationships. Because many-to-many relationships cannot be resolved, non-specific relationships do not
propagate any foreign keys. Many-to-many relationships are undesirable and should be removed as you
normalize your data model.
The following illustrates a non-specific relationship where the parent and the child are both optional. In the
Relationship Editor you can specify whether the parent and the child are optional or mandatory.
• Cardinality: Cardinality displays the ratio of related parent and child instances. The cardinality ratio for the parent
depends on whether the relationship is mandatory or optional. Although cardinality is a powerful concept for
expressing business rules, you should know that no database can directly enforce cardinality. Enforcing
cardinality constraints can be accomplished through procedural database logic or somewhere other than in the
database.
The iconic cardinality representations for IE (Crows Feet) notation are illustrated below:
Identifying
Relationship
Non-Identifying Relationship
Optional Mandatory
One to Zero or More Zero or One to Zero or More One to Zero or More
One to One or More Zero or One to One or More (P) One to One or More (P)
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 133