Building the Data Warehouse

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The entities that are shown in the ERD level are at the highest level of abstraction. What entities belong in the scope of the model and what entities do not are

An oval represents an entity, or major subject.

a 1:n relationship a 1:1 relationship an m:nrelationship

Figure 3.10 Representing entities and relationships.

determined by what is termed the “scope of integration,” as shown in Figure 3.11. The scope of integration defines the boundaries of the data model and needs to be defined before the modeling process commences. The scope is agreed on by the modeler, the management, and the ultimate user of the system. If the scope is not predetermined, there is the great chance that the modeling process will continue forever. The definition of the scope of integration should be written in no more than five pages and in language understandable to the businessperson.

As shown in Figure 3.12, the corporate ERD is a composite of many individual ERDs that reflect the different views of people across the corporation. Separate

Figure 3.11 The scope of integration determines what portion of the enterprise will be reflected in the data model.

user view (1)

Figure 3.12 The construction of the corporate ERD from the different user view ERDs.

user view (2)

user view (3) user view (n)

high-level data models have been created for different communities within the corporation. Collectively, they make up the corporate ERD.

The ERDs representing the known requirements of the DSS community are created by means of user view sessions, which are interview sessions with the appropriate personnel in the various departments.

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