The structure of a dimensional model is predictable. There is a single fact table at the center of the model. The fact table has one or more dimension tables related to it. Each dimension will have zero, one, or more hierarchical tables related to it.
The relationships are not usually complex. Relationships are always “one to many” in a configuration where the dimension is at the “one” end of the relationship and the fact table is the “many” end. Where dimensional hierarchies exist, the outer entity (farthest from the fact table) is the “one” end and the inner entity (nearest to the fact table) is the “many” end.
“One-to-one” and “many-to-many” relationships are rare, although this changes when “time” is introduced. There is no real need to model the cardinality (degree) of the relationships.
The participation conditions do not need to be specified. The dimension at the “one” end of the relationship always has optional participation. The participation condition for the dimension, or fact, at the “many” end is always mandatory.
Entity super/subtypes do not feature in dimensional models.
There is no requirement to name or describe the relationships as their meaning is implicit. It is important to show how the dimensional hierarchies are structured, but that is the only information that is needed to describe relationships.
There is no requirement for the fact table rows to have a unique identifier.
There is no requirement to model inclusive nor exclusive relationships.
The structure of a dimensional model is predictable. There is a single fact table at the center of the model. The fact table has one or more dimension tables related to it. Each dimension will have zero, one, or more hierarchical tables related to it.
The relationships are not usually complex. Relationships are always “one to many” in a configuration where the dimension is at the “one” end of the relationship and the fact table is the “many” end. Where dimensional hierarchies exist, the outer entity (farthest from the fact table) is the “one” end and the inner entity (nearest to the fact table) is the “many” end.
“One-to-one” and “many-to-many” relationships are rare, although this changes when “time” is introduced. There is no real need to model the cardinality (degree) of the relationships.
The participation conditions do not need to be specified. The dimension at the “one” end of the relationship always has optional participation. The participation condition for the dimension, or fact, at the “many” end is always mandatory.
Entity super/subtypes do not feature in dimensional models.
There is no requirement to name or describe the relationships as their meaning is implicit. It is important to show how the dimensional hierarchies are structured, but that is the only information that is needed to describe relationships.
There is no requirement for the fact table rows to have a unique identifier.
There is no requirement to model inclusive nor exclusive relationships.