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Re: Using the catalogue

From: Alexandr Savinov <spam_at_conceptoriented.com>
Date: Wed, 16 Nov 2005 14:12:18 +0100
Message-ID: <437b3042$1@news.fhg.de>


amado.alves_at_netcabo.pt schrieb:
> Suppose a RDBMS has a catalogue with schema
>
> Relations (Name) with key (Name)
> Fields (RelationName,FieldName,FieldType) with key
> (RelationName,FieldName)
>
> The catalogue is reflexive i.e.
>
> relation Relations contains { (Relations), (Fields) }
>
> relation Fields contains
> { (Relations, Name, Symbol),
> (Fields, RelationName, Symbol),
> (Fields, FieldName, Symbol),
> (Fields, FieldType, Symbol) }
>
> Suppose a database instance, and a query like
>
> all triplets (field name, value, relation), from any relation, such
> that field name is in {Name, Designation}, field type is String, and
> field value = "King"
>
> Please confirm that this query is impossible to express in SQL, and
> suggest other relational languages where it is possible. Tutorial D,
> Alaphor, the original relational calculus or algebra?
>
> Note that what is at stake is the capability of the language to
> transfer from field values to relation and field names. RDF has the
> corresponding capability in its data model. XQuery?

As far as I understand, this cannot be solved (easily) in traditional data models where relations and fields are dedicated elements with special role. This has significant advantages but the price we pay for them is also very high especially in the case of large systems.

However, I seriously doubt that the solution proposed by RDF can be qualified as satisfactory. The problem is deeper than it seems to be. (Although it is better than nothing.)

-- 
http://conceptoriented.com
Received on Wed Nov 16 2005 - 07:12:18 CST

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