Recognises an unmanaged duplicate column

K-601 · Skill knobit · Activity: Design the physical data model · Competence: Data modelling

A column copied from another table to save a join, with nothing keeping the copy equal to the original. The update anomaly the logical model removed, put back.

Can AI do this?

AI does this well Most of the tested AI models master this. 10 of 10 models master it.

Mastered means a probability of at least 90% that the model has this knobit, estimated from its graded answers. “Not shown” means the answers do not settle it either way. How the models are tested.

What it looks like in practice

Expected result: The copy, the original and what keeps them equal

How it is assessed: Flags the deficient case and passes the acceptable one. Deficient: account.holder_name copied from party.name for the account-servicing screen, no derivation, no DQ rule; the holder changes name and old accounts show the old one Acceptable: derivation names the source column and the mechanism that refreshes it, and a consistency DQ rule compares the two; or a view instead of a column. A copy meant to keep the value as at account opening is not a copy: the logical model says so (logical row 9)

Also known as: Unmanaged duplicate column (physical model)

Related knobits

Builds on

• K-502 Recognises an update anomaly in a logical data model
• K-651 Explains controlled denormalisation
• K-565 Explains derived data and point-in-time snapshots

Needed for

• K-704 Recognises a derived or copied column without a check

All 40 knobits of Design the physical data model.

Source: Review checklist 06-physical, row 1; Codd 1971; Kent 1983; E&N 1.6.1; C&B; S&W 12.6