Re: Very simple question to relational theorists.

On Friday, August 17, 2012 4:14:04 PM UTC-7, Evgeniy Grigoriev wrote:

> 1) About this thread. Here I just want to show that I can use such complex names to name relational attributes.

Understand.

> 2) I don't understand your remark about "special" operator. As I understand I can use any copmplex name to denote relation and any copmplex names to denote its attributes. This complexity means nothing for how this relation can be used. From the viewpoint of the formal relational data model, all these complex names are equal to names used to denote abstract relation R(a1, a2…). So usual relational opertion can be used, nothing special.

Read my message. Codd's relation operators are to be used in a certain way. You are building different ("special") operators. You are merely implementing yours in terms of his. You are using them and other non-relation operators to build yours that operate on relations specially. Your operators know about the special structure and disassemble it. (Pointer values or dotted attribute and variable names.) Codd's do not. You aren't even operating on relations: your operator behaviour depends on the names of variables, so your manipulated values are some kind of name+relation things. I told you, you are using relations non-relationally to implement/represent some relation-like and database-like things. As to whether the resulting things and operators are "relational" depends on details you didn't give.

> 3) About predicates and what I must associate with relation. Relational data model is abstract mathematics. Relation is a formal and meaningless data structure. If a data structure is equal to formal definition of a relation (I prefer to use the one given in "The Theory Of Relational Database" by David Maier) it is a relation. Relation doesn't have to tell something to DBA about the world to be relation. It's not only my viewpoint (http://www.dbdebunk.blogspot.com/2012/07/meaning-and-database-management.html#more)

I repeat, just using relations is **not** being relational.

The Maier book begins with "Each row in the table summarizes some object or relationship in the real world." At the dbdebunk link Hugh writes "The meaning of relation SP as understood by the user is: Supplier S# supplies part P# in a quantity of QTY". A formal system does not know meanings, but it produces meanings given other meanings. Codd's relation operators are designed specifically so that if the value of a relation is the set of all tuples that make its predicate true then a query result is the set of tuples that make its predicate true. That query meaning is in terms of the meanings of relations and meanings of the relation operators.

> 4) About my papers. I have another ones on ODBMS.ORG where the experimental system is described where this simple rule is implemented fully. But in this thread I want to show that dot in the name is just a part of name. Just a character. Nothing more. (Anyway, thank you very much that you read my paper :) )

I'll look.

> By the way, from my viewpoint the relation
> (1+2) 'DOC(ID, .No, .Lines.Item , .Items,Qty)
> is full of sence.

Yes, I expect that it is. And I expect that its meaning is in terms of the meaning of DOC.lines and the other dotless-attribute DOC and whatever special operator you are offering that produced it from them.

philip Received on Sat Aug 18 2012 - 09:29:29 CEST