Database Reference
In-Depth Information
Schema Revisions
Application enhancements generally require revisions to the database schema.
Depending on the type and extent of application enhancements, schema revisions
may comprise the following kinds of revisions:
•
Changes to data types or sizes of individual attributes
•
Additions of new columns to individual tables
•
Additions of new tables
•
Deletions of any redundant columns
•
Changes to uniqueness constraints
•
Inclusion of new foreign keys
The revisions to the database schema are first made in the test database
environment, tested, and only then applied to the production schema. Figure 17-5
illustrates how schema revisions are implemented.
Here are a few practical suggestions with regard to schema revisions:
Approval for revisions.
All revisions to database schema must be subject to serious
consideration and approval. Scrutinize the revisions and ensure that they do not
violate any standards. Extensive revisions must be treated with great care as if they
are part of the overall design.
Procedure for revisions.
Have a formal procedure establishing the method for
requesting, testing, validating, and approving the revisions. Include the users con-
cerned as part of the process. Identify the responsibilities and assign relevant tasks
to the DBA, programmers, analysts, and user representatives. Each revision must
follow the prescribed procedure.
TEST ENVIRONMENT
PRODUCTION ENVIRONMENT
Production
and test
schema
definitions
Production
version of
schema
definitions
DATA
DICTIONARY
DATA
DICTIONARY
DATA
DATA
Test instance
of
Production
instance of
Tested
versions
Limited copy
of production
data and
test data
DBMS
Production
data
DBMS
Production
versions of
needed
programs and
test versions
of revised
programs
Production
version of
each program
APPLICATION
PROGRAMS
APPLICATION
PROGRAMS
Figure 17-5
Database schema revisions.
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