how to make barcode in vb.net 2010 Dimension Roles and Aliasing in Software

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Dimension Roles and Aliasing
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Measurement of a business process can involve more than one instance of a dimension. When an auto dealer sells a car, for example, two employees are associated with the transaction: the salesperson who sold the car and the manager who approved the sale. These two relationships are called roles. In a fact table, they are represented by multiple foreign key references to the same dimension table. At query time, each role can be isolated by using a technique called aliasing.
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In a star schema, the multiple roles played by a dimension are represented by multiple foreign keys in the fact table. Database designers with a background in ER modeling are comfortable with this technique. It is not uncommon to have more than one relationship between the same pair of tables; ER models usually go so far as to name every relationship. For those unfamiliar with this technique, a brief example is warranted. A bank uses the star schema in Figure 6-7 to track mortgage settlements. A settlement is an event at which a loan application is signed and becomes a binding contract. The grain of the fact table is one row per settlement. The day dimension represents the date of the settlement, and the application dimension describes the mortgage application that goes into effect. In this example, when a mortgage goes into effect, there are three employees of the bank who are involved. The mortgage officer is the person who interacts directly with the customer, providing counsel on the types of mortgages available and helping the customer choose the right one. The mortgage processor s job is to gather documents from the applicant that will be used to assess his or her ability to repay a loan, such as bank statements, tax returns, and credit reports. The person who evaluates the application and approves it is known as the underwriter. In Figure 6-7, each of these employees is represented by a foreign key in the fact table: employee_key_officer, employee_key_processor, and employee_key_underwriter.
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DAY MORTGAGE_ SETTLEMENT_FACTS day_key application_key employee_key_officer employee_key_processor employee_key_underwriter mortgage_amount (additional facts) . . . APPLICATION
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EMPLOYEE: 3 Roles Officer Processor Underwriter
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MORTGAGE_SETTLEMENT_FACTS employee_ employee_ employee_ key_ key_ key_ day_key application_ officer processor underwriter key 338882 77777 201 336 557
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EMPLOYEE employee_ employee_name key_ 201 366 557 Eve Adelson Dan Roberts Chiu Mieng
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Multiple foreign keys: . Different key columns for different roles . All reference the same dimension table
Figure 6-7
Employee plays multiple roles in this fact table
Each of these three foreign keys refers to a row in the employee dimension as designated by an employee_key. An example of a row in the fact table is depicted in the bottom of the figure. In this sample row, the application represented by application_key 77777 contains employee_key_officer = 201. In the employee dimension table, employee 201 is someone named Eve Adelson. Similarly, the employee_key_processor refers to Dan Roberts, and the employee_key_underwriter refers to Chiu Mieng. It is possible that multiple roles are played by the same dimension instance. When this occurs, the fact table foreign keys for the roles will contain the same values. If Eve Adelson had been the mortgage officer and processor, for example, then employee_key_officer and employee_key_processor would each contain the value 201. TIP A dimension table can participate in more than one relationship with a fact table. Each relationship is known as a role.
Part III
PART III
Dimension Design
When a fact table refers to a dimension table, the foreign key column normally bears the same name as the corresponding primary key column. This is not possible when there are two or more roles. Instead, the foreign key columns should be given names that connote each role. The designation of a standard can help here. In Figure 6-7, for example, the three foreign key references to employee append role descriptors to the key name from the employee table: employee_key_officer, employee_key_processor, and employee_key_ underwriter. This makes each role readily identifiable when examining column names in the fact table. Every time a dimension table is referred to by a fact table, the relationship represents a role. Even if there are not two relationships, it can be useful to name the role designated by each join. This is particularly helpful with time dimensions, which play a different role in each star. In Figure 6-7, for example, the role of the day dimension is day of settlement. Identifying this context provides useful documentation of the star and may be particularly handy when building drill-across reports.
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