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20/12/1999 06:06:51
Walter Meester
HoogkarspelPays-Bas
 
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Divers
Thread ID:
00305642
Message ID:
00306026
Vues:
82
>Walter,
>
>>>There is no product on the market that meets Codd's rules completely. Some meet more of them than others and xBase is somewhere at the bottom of the list on this point.
>>
>>As far as I know SQL is not number 1 on this list too.
>
>As I said before, there is NO true RDBMS available on the market today.

As for the bottom of the list, i'd like to see it climb a few places.

>>>Codd's whole point is that a relational product will not have any way to access the data other than the relational way. If there is another way then the product is not relational.

>>In this part I disagree. I've recently had a discussion if C++ was a pure object orient language. By definition a language is a pure OO when it does not have ways to violate the OO rules. C++ certainly has functionality to violate the OO rules, but does this make the language less OO ? I think not.

>Walter, Yyou can disagree with Codd if you like, but his rule number 0 was "The only way to access the data is through the relational operations."

>>To me this argument is not that important. BTW if you read John Petersen messages, you'll discover that SQL-server also have record oriented operations. Does it make the product less Relational. IMO not.

>Yes, it does make SQL Server less relatinal. As a mater of fact, taking Codd's original 13 rules for being a relational database management system it totally negates SQL Server as relational.

So where do we stand now? How does this involve my wish? I want more Relational behavour in the product, but to me you're saying, you cannot have it because Fox will never be relational. It does not make sense to me.

>>My argument was based on that generated Pk are not a part of the logical design.
>They most certainly are part of the logical design. They are added to the entity schema at the logical design time.

Since this another issue, we've discussed througely before, lets skip this part.

>We can implement relational designs and manipulate relational database systems.

Hold on a second, 'we can manipulate relational database systems'? I thought we agreed there ARE NO RDBMSs ?

>That does not make the product itself an RDBMS.
Agreed, so ?

Nope, but as I said before, I would like to see more RDBMS properties into the product.

>>>Relational database theory and SQL were both invented by E. F. Codd while he was working for IBM in the 70's.
>>
>>Have you any docs to back this up ? I've got trouble to believe this. From what I know is that Codd invented the relational language, which is in fact less restrictive than SQL. SQL is derived from that language.
>
>Not off the top of my head. However, theer is an error in your statemtns. Relatinal databse theory is a mathematical theory with mathematical proofs of validity in manuipulating sets of data. SQL is the language that Codd developed to work with relational data. So SQL is the language and Relational Theory is the basis for the design methodology.

DATE describes the relational language in it's book and discusses the differences between this (theorectical) language and SQL. as far as I'm concerned THIS is the relational language, NOT SQL.

>I am not arguing that your wish could or could not do all of the things needed in manipulating the data. I am agruing that I don't think implementing your wish is a valauble thing for the MS developers to spend their time on.

I think this could be a missed opportunity, because all (R)DMBSs I know of suffer the same problems related to SQL's copying mechanism. when VFP got its own database (DBC) with validations and RI (though implemented by triggers) it was a step forward to the relational theory, I think we should not hesitate to take the next.

Walter,
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