# Re: What databases have taught me

Date: Fri, 30 Jun 2006 21:23:46 GMT

Message-ID: <CDgpg.4287$pu3.100814_at_ursa-nb00s0.nbnet.nb.ca>

Marshall wrote:

> Bob Badour wrote:

*>
*

>>Marshall wrote: >> >>>Mmmm, what I was trying to point out is that it is a somewhat >>>OOish idea to consider functions on a type as part of the >>>definition of that type. >>> >>>Given a set A, and a set B. >>>Given a function f: A -> B >>> >>>We would not *necessarily* consider f as part of the definition of A. >> >>I would. I wouldn't necessarily require all operations defined on a type >>be declared to the dbms, but the type is a set of values and a set of >>operations on those values.

*>*

> Are you saying you "would consider f as part of the definition of A"

*> or are you saying you "would necessarily consider f as part of the*

*> definition of A."*

That depends on whether A is a data type or a set. A data type is a set of values and the set of operations defined on those values. (Note that is data type as opposed to the myriad other uses of 'type'.)

*> Other question:
**>
*

> given:

*> f: A, B -> C
**>
**> is f part of the defintion or A, or of B, or both? What about C?
**>
**> Just curious.
*

f is defined on all three A, B and C. Thus f is part of the definitions of three data types.

> Marshall

*>
**> PS. While you are at it, I need 500 words or more on
**> "what I did during my summer vacation" by next Tuesday.
*

Hey! I know it sometimes seems otherwise, but this is comp.databases.theory and not comp.databases.do.my.homework.for.me! Received on Fri Jun 30 2006 - 23:23:46 CEST