Building the Data Warehouse

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34.    What audit requirements are there? How will audit requirements be met?

ISSUE: As a rule, system audit can be done at the data warehouse level, but this is almost always a mistake. Instead, detailed record audits are best done at the system-of-record level.

35.    Will compaction of data be used? Has the overhead of compacting/decom-pacting data been considered? What is the overhead? What are the savings in terms of DASD for compacting/decompacting data?

ISSUE: On one hand, compaction or encoding of data can save significant amounts of space. On the other hand, both compacting and encoding data require CPU cycles as data is decompacted or decoded on access. The designer needs to make a thorough investigation of these issues and a deliberate trade-off in the design.

36.    Will encoding of data be done? Has the overhead of encoding/decoding been considered? What, in fact, is the overhead?

ISSUE: (See issue for question 35.)

37.    Will meta data be stored for the data warehouse environment?

ISSUE: Meta data needs to be stored with any archival data as a matter of policy. There is nothing more frustrating than an analyst trying to solve a problem using archival data when he or she does not know the meaning of the contents of a field being analyzed. This frustration can be alleviated by storing the semantics of data with the data as it is archived. Over time, it is absolutely normal for the contents and structure of data in the data warehouse environment to change. Keeping track of the changing definition of data is something the designer should make sure is done.

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