Conceptual – Logical – Physical

One would assume that a speaker on a Data Management Conference got the distinction between conceptual, logical and physical right? Well … no :)

It’s very common to define these terms based on the level of detail they contain. There are a few things wrong with this definition:

First, it completely ignores what we know about idealization. Idealization is the idea that defines terms like conceptual, logical and physical. People familiar with the Zachman framework will recognize this.

Secondly, it’s a very ambigious defition. What if I add a small detail to a conceptual model, did it just became logical? If not, what if I add this other small detail?

These are the definitions I use, based on idealization:

Conceptual Model. A model describing a system where there is complete abstraction of any implementation with an information system.

Logical Model. A model describing a system where we don’t abstract away a realisation with an information system, meaning we have to make design choices, but we still abstract away the technology used.

Physical Model. A model where neither the fact it is implemented using a particular information system nor the technology used, is abstracted away.

You can still have ‘very detailed’ or ‘high level’ if you want, since that is ortogonal to the above. You can have a high level physical model or a very detail conceptual model.