Populating the Fact Table
When you perform a full build of a cube, the system iterates through the records of the base table. For each record, the system does the following:
-
Examines the definition of each level and obtains either no value, a single value, or multiple values.
In this step, the system determines how to categorize the record.
-
Examines the definition of each measure and obtains either no value or a single value.
The system then writes this data to the corresponding row in the fact table and updates the indexes appropriately.
When you perform a Selective Build, the system iterates through an existing fact table and updates or populates the selected columns.
Determining the Values for a Level
Each level is specified as either a source property or a source expression. Most source expressions return a single value for given record, but if the level is of type list, its value is a list of multiple values.
For a given record in the base table, the system evaluates that property or expression at build time, stores the corresponding value or values in the fact table, and updates the indexes appropriately.
For example, the Age Bucket level is defined as an expression that returns one of the following strings: 0-9, 10-19, 20-29, and so on. The value returned depends upon the patient’s age. The system writes the returned value to the fact table, within the field that corresponds to the Age Bucket level.
For another example, the Allergy level is a list of multiple allergies of the patient.
Determining the Value for a Measure
When the system builds the fact table, it also determines and stores values for measures. Each measure is specified as either a source property or an ObjectScript source expression.
For a given row in the base table, the system looks at the measure definition, evaluates it, and stores that value (if any) in the appropriate measure field.
For example, the Test Score measure is based on the TestScore property of the patients.
Determining the Value for a Property
When the system builds the fact table, it also determines values for properties, but it does not store these values in the fact table. In addition to the fact table, the system generates a table for each level (with some exceptions; see Details for the Fact and Dimension Tables). When the system builds the fact table, it stores values for properties in the appropriate dimension tables.
