Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Jon Heggland wrote:
> In article <dSCwe.133254$g25.7165020_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...

>>
>>Who needs rows? We only have objects (or identities) and binary 
>>relationship between objects and values (attributes, like between a user 
>>and an e-mail address) and between objects and objects (relationships, 
>>like between a person and person-details). [...] 

Yes, correct.

>>>>Yes, that is at the core of my suggestion: a decent theoretical
>>>>foundation for opaque keys, abstract identifiers, or whatever you want
>>>>to call them.

In some sense, but it would be a bit like saying that references fulfill the purpose of pointers you don't do pointer-arithmetic with. That's true, but it misses the essence. Opaque keys would come with a formalization that better captures what they mean and how they should be treated. It's the difference between informally stating that certain fields are surrogate keys and waving your hands a bit, and coming up with a precise formal theory of what that exactly means.

> [...] Perhaps I am skeptical to
> your proposals because from my point of view, identity separate from
> value makes thing more complicated, not simpler. And/or because looking
> at everything as objects/entities and relationships is a too restrictive
> worldview for me. I guess I would be happier if this was presented as a
> layer on top of the RM instead of as a replacement.

Well, if that makes you happier then by all means let us present it as such. :-) So where do you get the feeling hat this worldview would be somehow restrictive? What do you think that becomes more difficult to model?

> Anyway, there is one thing that is bugging me when I read articles about
> object data models like Calvanese/Lenzerini and Van den Bussche /
> Paredaens. If objects are just identity points, and the properties of
> objects are other objects, where do actual data values enter into the
> picture?

Data values are special objects that have one or more representations associated with them by which they are identified. Like LOTs and NOLOTs in NIAM.

• Jan Hidders