Re: Database-valued attributes?

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:_C_rb.122225$9E1.607217_at_attbi_s52...
> There's been the occasional incidental discussion of relation-valued
> attributes on the list lately. This has got me thinking: what about
> database-valued attributes? That is to say, what about an attribute
> that consists of a set of relation values?
>
> The reason I ask is because I have been thinking about expressing
> trees as values. The canonical logical representation of a tree from
> "Practical Issues in Database Management" is a pair of relations:
> one for nodes, one for edges.
>
> If one wanted to have an attribute that belonged to the tree domain,
> one would need to support an attribute with such a pair of relation
> values.
>
> Does this raise any problems? I don't see any immediate issues, but
> it's not an idea I've ever heard mentioned anywhere else.
>
> Comments welcome, including alternative ideas.

All you have done is describe a data type with a possrep consisting of two RVA's. Such a data type is perfectly acceptable. The equivalent of a "database value" with multiple views would be a similar type with multiple possreps. Received on Tue Nov 11 2003 - 13:26:42 CET