Building the Data Warehouse

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The third construct is the connector. The connector relates data from one grouping to another. A relationship identified at the ERD level results in an acknowledgment at the DIS level. The convention used to indicate a connector is an underlining of a foreign key.

The fourth construct in the data model is “type of” data. “Type of” data is indicated by a line leading to the right of a grouping of data. The grouping of data to the left is the supertype. The grouping of data to the right is the subtype of data.

These four data modeling constructs are used to identify the attributes of data in a data model and the relationship among those attributes. When a relationship is identified at the ERD level, it is manifested by a pair of connector relationships at the DIS level. Figure 3.15 shows one of those pairs.

At the ERD, a relationship between customer and account has been identified. At the DIS level for account, there exists a connector beneath account. This indicates that an account may have multiple customers attached to it. Not shown is the corresponding relationship beneath the customer in the customer DIS. Here will be a connector to account, indicating that a customer can have an account or accounts.

Figure 3.15 The relationships identified in the ERD are reflected by connectors in the DIS. Note that only one connector—from acctno to customer—is shown in this diagram. In reality, another connector from customer to acctno would be shown elsewhere in the DIS for customer.

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