Re: About grammar and syntax on a possible relational language

On Mar 12, 8:33 am, Cimode <cim..._at_hotmail.com> wrote:
> On Mar 11, 5:38 pm, Cimode <cim..._at_hotmail.com> wrote:
>
> > > Why not:
> > > [MAKE RICH_EMPLOYEE = {EMPLOYEE WITH SALARY > 100000}]
> > > (with curly braces around the derivation expression)? It seems a
> > > little "off" to use them only sometimes.
>
> > Because I reserved '[]' to relation operation and '{}' to relation
> > definition.  I will keep the remark in mind though
>
> To be more explicit {} is attribute level manipulation and [] is
> relation level manipulation to keep the language as versatile as
> possible.  For example
>
> [MAKE R0 = {ATTRIBUTE0_1, ATTRIBUTE0_2}]
> [MAKE R1 = {ATTRIBUTE1_1, ATTRIBUTE1_2}]
> [MAKE R2 = R0 UNION R1]
> PRESENT2D [R2]
>
> does the same thing as
>
> PRESENT2D [{ATTRIBUTE0_1, ATTRIBUTE0_2} UNION {ATTRIBUTE1_1,
> ATTRIBUTE1_2}]
>
> It is also about the coherence of the computing model behind.  The
> input of the media layer is necessarily a relation.  The input of the
> logical layer may either be a relation or an attribute set.

I see what you're aiming for and I think that I agree with the syntax. The example that introduced the confusion for me is this: [MAKE VIP_MEMBER = {RICH_EMPLOYEE}] where "RICH_EMPLOYEE" refers to a relation.

TroyK Received on Wed Mar 12 2008 - 17:29:17 CET