# Re: Can relvars be dissymetrically decomposed? (vadim and x insight demanded on that subject)

Date: 17 Jul 2006 11:28:35 -0700

Message-ID: <1153160915.418315.93000_at_h48g2000cwc.googlegroups.com>

Cimode wrote:

> [snip]

*> > > [snip]
**> > > For instance, if you consider the function F(X) = A(X) and you add
**> > > the value B to F(X), you are basically doing a translation making a new
**> > > function T(X) = F(X) + B = A(X) + B In this case, the result of adding
**> > > B to the function can be expressed (characterized) as a mathematical
**> > > translation (jumping from F(X) to T(X)). It says a lot about the
**> > > function F(X) behavior and may help describe it better over time.
**> >
**> > But F isn't changing. You're creating a new function, not changing an
**> > existing one. Assuming the expression F(X)+B makes sense, T has the
**> Now that's finally getting interesting... If I follow your reasoning
**> that would mean that once an INSERT is done, there would be necessarily
**> a new relation resulting from the INSERT operation performed?
*

> > > The

*> > > challenge of this thread is to do a similar effort on relations. For
**> > > instance, an interesting question raised would be: is an INSERT
**> > > operation equivalent to a translation in relational perspective?
**> I rephrase then : is an INSERT operation equivalent to a translation in
**> relational perspective resulting in a new relation?
*

Any relational expression produces a relation value. If that's what you mean by the "new relation," then yes. If it's an UPDATE/INSERT/DELETE, that value is then assigned to the relvar, so the relvar has a new value - maybe that's what you mean.

> > > Overall, how does a relation R1 *changes* when an INSERT, UPDATE,

*> > > DELETE operation is made on it? Characterizing such change would help
**> > > describe better relations themselves.
**> Are operations in general performed on relations create new relations.?
*

Expressions (relational or otherwise) evaluate to values, which in the case of relational expressions are relations. "Create new" doesn't have much meaning in that context.

- erk