CODASYL BDAM DML   Oracle Tips by Burleson Consulting

High Performance Data Warehousing

The CODASYL Generation Of Database Management 

There were several advantages to the CODASYL approach, primarily with performance and the ability to represent complex data relationships. In the following example, BDAM is invoked for the OBTAIN CALC CUSTOMER statement, and linked lists are used in the statement OBTAIN NEXT CUSTOMER WITHIN CUSTOMER-ORDER.

For example, to navigate a one-to-many relationship, (i.e., to get all of the orders for a customer), a CODASYL programmer would enter the following code:

MOVE 'IBM' to CUST-ID.
OBTAIN CALC CUSTOMER.
PERFORM ORDER-LOOP UNTIL END-OF-SET.

ORDER-LOOP.
OBTAIN NEXT ORDER WITHIN CUSTOMER-ORDER.
MOVE ORDER-NO TO OUT-REC.
WRITE OUT-REC.

As a visual tool, the set occurrence diagram, shown in Figure 1.8, has great potential for understanding internal data relationships. The relationships between the objects are readily apparent, and the programmer can easily visualize the navigation paths. For example, in the sample diagram, you can easily see that order 123 is for 19 pads, 3 pencils, and 12 pens. Cross over to the item side of the diagram, and you can easily see which orders include pens. For systems that physically link objects, the set occurrence diagram is an extremely useful visual tool.

Figure 1.8 The set occurrence diagram.

Although the design of the CODASYL network model is very elegant, there were serious problems with the ongoing use of network databases. Network databases, much like hierarchical databases, are very difficult to navigate and administer. Learning the Data Manipulation Language (DML), especially for complex navigation, is a skill acquired through many months of training.

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This is an excerpt from "High Performance Data Warehousing", copyright 1997.

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