# Re: Function

From: Kira Yamato <kirakun_at_earthlink.net>

Date: Tue, 15 Jan 2008 14:14:45 -0500

Message-ID: <2008011514144516807-kirakun_at_earthlinknet>

>>>>> [Codomain]

>>>>> 2. A domain is a set of values: for example

>>>>> 3. Domain of a function. See function, math context.

>>>>> [Function]

>>>>> Three different contexts, but just about the same meaning:

Date: Tue, 15 Jan 2008 14:14:45 -0500

Message-ID: <2008011514144516807-kirakun_at_earthlinknet>

On 2008-01-15 11:29:40 -0500, mAsterdam <mAsterdam_at_vrijdag.org> said:

> Kira Yamato schreef: >> mAsterdam said: >> >>> vldm10 wrote: >>>> [...] >>> How about this: >>> cdt glossary proposal: >>>

>>>>> [Codomain]

*>>>>> See function, math context.**>>>>>**>>>>> [Domain]**>>>>> 1. Given a relation R, a domain is a set Sn such**>>>>> that for each tuple (A1, A2, ...An, ...Am) in R,**>>>>> An is an element of Sn.*>> >> This is not good enough. > > Could you provide a better text?

A domain is simply a set of values.

> >> It is possible that a value exists in the domain Sn yet the relation >> has no corresponding tuple which holds that value for An. > > Does the current text forbid that?

In your original definition, you require a tuple in R that holds that value in order for that value to be in Sn.

I'm saying that this requirement is not needed.

>

>>>>> 2. A domain is a set of values: for example

*>>>>> "integers between 0 and 255",**>>>>> "character strings less than 10 characters long",**>>>>> "dates".**>>>>> Sometimes used synonymously with type.*>> >> This seems right. A domain is just a set of values. In relational >> algebra, this set is required to be non-empty since attributes are >> non-null. > > It is worm season, it seems :-)

Yea. Some relational algebra textbooks make a big case of why attributes should not be null.

>

>>>>> 3. Domain of a function. See function, math context.

>> >> On the other hand, mathematics does not require a domain to be non-empty. >>

*>>>>>**>>>>>**>>>>>*>>>>> [Function]

*>>>>> For now we have to live with different meanings**>>>>> of _function_ when talking about databases:**>>>>> "The function of this function is to get the tuples from B**>>>>> that are functionally dependant on A."*>> >> No, there is always just one meaning of function in database. > > Would s/meanings/uses/ take away your objection? > If not, which one meaning?

Perhaps s/meanings/definition/ is better.

>

>>>>> Three different contexts, but just about the same meaning:

*>>>>>**>>>>> 1. General**>>>>> A purpose or use.**>>>>>**>>>>> 2. Math**>>>>> A binary mathematical relation over two sets D and C that associates**>>>>> with each element in D exactly one element in C.**>>>>> Set D is called the domain of the function, C its codomain.*>> >> Essentially correct, although to be rigorous you need to define how >> such binary relation can define the meaning of "associating each >> element in D exactly one element in C." >> >> Not all binary relation has this property. > > IMHO this goes way beyond the glossaries purpose. > However, if you have a simple replacement that would cover this it > would be welcome.

It is over the top for practical uses. I was just being pedantic. :)

> [...]

-- -kiraReceived on Tue Jan 15 2008 - 20:14:45 CET