Topic: database change management

Summary

Databases change frequency. New, updated, and deleted rows happen continuously. Each change may update numerous indices. Triggers and constraints may cascade. For example, deleting a row may automatically delete dependent rows in other tables.

Furthermore, database administrators add new tables, new columns, new indices, and reorganize existing tables. These schema changes require careful management. Existing applications must continue to run, while new applications subtly change the meaning of data.

Periodically, a database may migrate to a new schema. For example, the underlying software may need upgrading to a new version. If so, the database may require thorough checking for inconsistencies, migration to the new format, and reverification. These steps must be quick and accurate, otherwise downtime may be excessive. New types may define type migrators to support older applications (e.g., the view mentioned previously).

Distributed databases make change more complicated. A change to one physical database may need corresponding changes in multiple databases. (cbb 8/06)

Subtopic: automatically handle change

Quote: arbitrary changes to database schemas are needed for a design environment [»zdonSB10_1986]

Quote: changes in an integrated database are automatically made everywhere

Quote: a database could activate a module whenever data is modified or the situation matches a pattern; this defines the application's control structure [»balzRM_1986]

Quote: an interactive database should converge to a consistent state [»stefM1_1987]

Quote: over time databases expand and some information may be dropped; applications easily adjusted [»coddEF_1990]

Subtopic: objects with out-of-date types

Quote: what happens to old objects and their programs when a type definition changes; assumptions will no longer hold [»zdonSB10_1986]

Quote: handle modified types by defining error handlers for each version; these handlers fixup an old version's behavior [»zdonSB10_1986]

Subtopic: inheritance

Quote: inheritance is important for management of change, especially long-term [»wegnP10_1986]

Subtopic: personal information

Quote: in Lisa List, you can rearrange columns or add new ones at any time [»stewG3_1983]

Quote: Lisa List can add or change fields at any time; allows any amount of text [»willG2_1983]

Quote: a personal information system must allow free format text, dynamically defined structure, and arbitrary report formats [»kaplSJ7_1990]

Quote: without a fixed field/value orientation, Agenda can present data in any format

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