The relational mistake

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Not quite

A relation is a function between sets. Relations and sets are not synonymous, though a relation is a set.

For example I take the set of all names and the set of all dates of birth and define a relation between them (note that this will give every relation between name and date of birth, not the date of birth of every person).

However I can hardly be expected to explain in this short space what should be basic knowledge for any practitioner who goes anywhere near a SQL-DBMS. I recommend C. J. Date's "Database in Depth" or "Applied Mathematics for Database Professionals" by Lex de Haan and Toon Koppelaars (a new and outstanding contribution to the literature).

Another important point, Codd definitely did not define the relational model as a data STORE. The relational model has nothing to say about data storage, its a mathematical model for REPRESENTING data. How the data is stored is irrelevant - from this one might also note that from a user or programmer perspective whether the data is on disk or in memory is wholly irrelevant, the only important thing is that if the system crashes it returns to the last definable logically consistent state.

Lastly although CRUD may be a way of making some of the concepts familiar to die hard DP guys, insert, update, delete and select are NOT relational operators, just occasionally convenient shortcuts - sadly SQL doesn't support the relational way of doing these things (just the cruddy ones I guess).

Saying you create, update or delete anything is a little bit like saying you create a new number when you say X = 20.

Posted by: jorwell   Posted on: 10/31/07 You are currently: a Guest | Members login | Terms of Use

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