# Defining a transformation function between sets

• May 20th 2011, 08:38 AM
klendo
Defining a transformation function between sets
Hello,

I'm writing a work and I do not really know which is the best way to specify the following transformation function. Let me introduce it by a simple example.

Let us supose that we have defined a tuple of objets and relationships at a given moment $t$:

$T^t=\langle O^t,drives^t\rangle$

the set of objects is $O^t=\{P^t,C^t\}$, where:
$P^t=\{person1,person2\}$
$C^t=\{car1,car2\}$

and the relationships are $drives^t=\{drives(person1,car1),drives(person2,car 2)\}$

Given an initial tuple at moment $t$, I want to define a transformation function $\delta$. This function consists in applying the required changes (in terms of addition or deletion) in order to obtain an specific tuple at moment $t'$. That is, let us supose that the tuple that is wanted to be reached at moment $t'$ is the following:

$T^t'=\langle O^t',drives^t'\rangle$, where:

$O^t'=\{person1,person2,person3,car1,car2,car3\}$
$drives^t'=\{drives(person1,car3),drives(person2,ca r2),drives(person3,car1)\}$

Then, in order to obtain the final tuple from the initial tuple, we require to apply a set of changes $\tau$:

$\tau=\{add(person3),add(car3),delete(drives(person 1,car1)),add(drives(person3,car1)),add(drives(pers on1,car3))\}$

and here is when I don't know which is the best way to say the next:
A transformation function $\delta$ defines how a given tuple at a initial moment, can be transformed into another tuple at a final moment, that is, the changes that must be applied to the initial tuple at moment $T^t$ in order to obtain the final tuple at moment $T^t'$:

$\delta: T^t \times \tau \rightarrow T^t'$

But I think this is not correct, may be better in the following way??
$\delta: 2^T^t \times \tau \rightarrow 2^T^t'$
or this one??:
$\delta: 2^T^t \times 2^{\tau} \rightarrow 2^T^t'$

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Now let us supose that the relationship $drives$ consists on a function between a pair of objects such that, if returns 0 means that the person does not drive the car, if returns 1, the person drives the car:
$drives^t: P^t \times C^t \rightarrow \{0,1\}$

If I write this relationship in this way, I could say that a change of addition means that the funcion returns 1 and a change of deletion means that the function returns 0?? How I should specify this??

May I use the same notation than the first one?? I mean, may I say that exists a set of changes $\tau$, such that, when applied to the initial tuple we obtain the final one??

If this is correct, how I could write that a change of addition between a pair of objects $person_i$ and $car_i$ means that $drives^t'(person_i,car_i)=1$ and a change of deletion means that $drives^t'(person_i,car_i)=0$ ??
How could I write this??

That's all. If someone could help me I would be very grateful

Thank you.
• May 23rd 2011, 02:37 AM
klendo
Up.