# Thread: A question in Set Dependency prof

1. ## A question in Set Dependency prof

Dear All,

I am trying to find a mathematic prof for the following question and i also would like to know what do you call this problems in mathematic term so that i could find the right materials in web.

The question

you have the table that consist of severals attributes a1,a2,a3,a4,...,am with numbers of rows Rn. There is a dependency between attributes. For example, a1 -> a3 (as postcode -> suburb). Similarly, a2->a4 (job titles->income).
The thing that i would like to know is it true to say
if
a1->a3 and a2->a4
then
{a1,a2}->{a3,a4}

I also appreciate if you could recommend some web site that discuss this concept.

2. This questions seems to be coming from database theory. I don't know off top of my head any web sites that are devoted to it, but I am sure there are plenty and that basic textbooks on databases discuss this.

To discuss this outside of database context, one has to define dependency and {a1, a2} (is it an ordered pair? unordered pair?). I guess there is a dependency between two columns of a table if these columns define a function, i.e., for each value in the first column there is one and only one value in the same row in the second column. Then yes, if a3 depends on a1 and a4 depends on a2, then there is a dependency between two columns a1, a2 viewed as a column of ordered pairs and two columns a3, a4.

3. Originally Posted by Nont
Dear All,

I am trying to find a mathematic prof for the following question and i also would like to know what do you call this problems in mathematic term so that i could find the right materials in web.

The question

you have the table that consist of severals attributes a1,a2,a3,a4,...,am with numbers of rows Rn. There is a dependency between attributes. For example, a1 -> a3 (as postcode -> suburb). Similarly, a2->a4 (job titles->income).
The thing that i would like to know is it true to say
if
a1->a3 and a2->a4
then
{a1,a2}->{a3,a4}
Well, that depends upon what you mean by "{a1,a2}->{a3,a4}". If you mean it simply as shorthand for "a1->a3" and "a2->a4", then, yes, of course, if "a1->a3" and "a2->a4" then "{a1, a2}-> {a3, a4}". That follows just from the definition of "{a1, a2}->{a3, a4}". If you mean something else by that, we would need to know what you mean by "{a1, a2}->{a3, a4}".

I also appreciate if you could recommend some web site that discuss this concept.