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Resolving the Dimension Key Using Lookup

If the dimension key is not provided to the ADI through database joins, the ADI performs the lookup in the dimension table. The ADI does this using prepackaged lookup transformations.

The ADI uses the Dimension Key ID, the Source ID and Lookup date in looking up the dimension key. All these columns are necessary for the ADI to return the dimension key. The ports are described in Table 23.

In Figure 31, the Supplier Products Key Lookup transformation illustrates the three input columns needed for the ADI lookup—the Key ID, Source ID, and Date (lookup date). The transformation then outputs the Supplier Product key (the dimension key) to the data warehouse table IA_SPLR_PRODS.

Figure 31. Example of Input Columns Required for the ADI

If Type II slowly changing dimensions are enabled, the ADI uses the unique effective dates for each update of the dimension records. When a dimension key is looked up, it uses the fact's primary date to resolve the appropriate dimension key.

The effective date range gives the effective period for the dimension record. The same entity can have multiple records in the dimension table with different effective periods due to Type II slowly changing dimensions. This effective date range is used to exactly identify a record in its dimension, representing the information in a historically accurate manner. In the lookup for Employee Contract Data shown in Figure 32, you can see the effective dates used to provide the effective period of employee contracts.

Figure 32. Effective Dates Used in Slowly Changing Dimension