Re: About grammar and syntax on a possible relational language

On 13 mar, 21:00, TroyK <cs_tr...@xxxxxxxx> wrote:
On Mar 12, 11:33 am, Cimode <cim...@xxxxxxxxxxx> wrote:



On Mar 12, 4:29 pm, TroyK <cs_tr...@xxxxxxxx> wrote:

On Mar 12, 8:33 am, Cimode <cim...@xxxxxxxxxxx> wrote:

On Mar 11, 5:38 pm, Cimode <cim...@xxxxxxxxxxx> 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

Basically if I write down

1) [MAKE VIP_MEMBER = {RICH_EMPLOYEE}]
or
2) [MAKE VIP_MEMBER = {MEMBER RICH_EMPLOYEE}]

I am defining VIP_MEMBER as having one attribute of type RICH_EMPLOYEE
(named RICH_EMPLOYEE in case 1 or MEMBER_RICH in case 2) while if I
write

[MAKE VIP_MEMBER = [RICH_EMPLOYEE]] I am actually equating the
relation VIP_MEMBER and the relation RICH_EMPLOYEE. Both are in fact
valid. It just depends if we are working at relation level or at
attribute level.- Hide quoted text -

- Show quoted text -

I think I'm getting tripped up over whether the declaration is of a
new relation (called VIP_MEMBER that has (a) one attribute that is a
relvar, or (b) one attribute that is a relation.
An un-ary relation is *de facto* is a type.
When using {}, (b) is correct

Is this syntax:
[MAKE VIP_MEMBER = [RICH_EMPLOYEE]]
a view definition, or an assignment?
A relation level assignment. Not a view.
When running...
[MAKE VIP_MEMBER = [RICH_EMPLOYEE]] I am creating a new relation whose
body is independent from RICH_EMPLOYEE. As soon as an operation
impacts any of the two bodies, the two relations do not equate
anymore.

As a consequence, if I then run
[MAKE VIP_MEMBER = VIP_MEMBER - {1, 1} ] --> delete
[MAKE RICH_EMPLOYEE = RICH_EMPLOYEE - {1, 2} ]

VIP_MEMBER and RICH_EMPLOYEE relation are not equal anymore because
only their header and constraint set are equal.

By the way, I should have prefaced my first response to the thread
with the disclaimer that I'm by no means a language designer, so you
can feel free to take my comments with a grain of salt.
I am trying to gain a feedback and perception from all users that can
help me sharpen the language. You help is appreciated.
TroyK

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