Fact entity

Fact entities group measures (facts) that share dimensions at the same level of granularity. The fact entity is the core entity of a dimensional data structure. All or a subset of the measures and dimensions that are held in a fact entity may be used by one or more downstream data marts. The measures in the fact entities support the measures defined in the analytical requirements.

About fact entities

A fact entity is defined at a low level of granularity and with a number of dimensions that make its measures (facts) reusable in multiple aggregate fact entities. An instance of a fact entity represents the occurrence of an actual business transaction. It holds aggregated or snapshot measures resulting directly from such business transactions at a detail level.

Properties

Name (mandatory)

A textual name that identifies the fact entity in title case (all words start with a capital letter).

e.g. fact entity Meter Reading Fact
e.g. fact entity Asset Lifecycle Fact

Dimensional type (mandatory)

The dimensional type is set to Fact for all fact entities.

Owning package (mandatory)

The owning package to which the fact entity belongs.

e.g. package Meter owns fact entity Meter Reading Fact
e.g. package Asset owns fact entity Asset Lifecycle Fact

Description (mandatory)

A complete and unambiguous description of the fact entity.

Persistent (mandatory)

A flag that indicates whether the entity is persistent or not. All entities of the delivered model are set to persistent. When the persistent flag is enabled, the entity is included in the scope of the practitioner, project, or enterprise data model.

Note: a persistent entity is physically implemented when you transform the logical data model into a physical data model. When you harvest the data model, take care when you use the persistent flag. For example, project A can decide to include an entity, but project B can decide not to include it. When you harvest project A at the enterprise level, the entity is set to persistent, indicating that the entity is part of the enterprise data model. Afterward, when you harvest project B at the enterprise level, keep the entity as persistent, although project B does not include it.

Measure attributes (mandatory)

The measure attributes that describe the fact entity. Measure attributes are defined as having the following characteristics: regular aggregate and semi-aggregate.

e.g. measure attribute Purchased Count describes fact entity Asset Lifecycle Fact

Relationships (mandatory)

One or more relationships to the dimension entities, on which the measures of the fact entity can be analyzed. Each relationship indicates an axis of analysis for the measures in the fact entity. Each fact is related to the appropriate version of a dimension entity instance.

e.g. dimension entity Meter is parent of relationship Meter Reading Fact_Meter_FK with fact entity Meter Reading Fact

Primary key (mandatory)

By convention, the name of the primary key is the name of the fact entity suffixed with PK.

e.g. primary key Meter Reading Fact PK is the primary key of fact entity Meter
e.g. primary key Asset Lifecycle Fact PK is the primary key of fact entity Asset Lifecycle Fact

Assigned terms (optional)

The assigned terms maintain traceability between the DWM elements and the vocabulary. A fact entity may be mapped to a business term in the vocabulary.

e.g. business term Meter reading is assigned to fact entity Meter Reading Fact