Re: Hierarchies in the relational model

Paul wrote:
> I wonder if these additions can be somehow incorporated into an
> extended relational model instead of being added on as a kind of
> afterthought? And whether such a thing is in fact necessary or
> desirable?

Instead of transitive closure operator can I alternatively suggest a distance function? Suppose we have

table graph (

    tail integer,
    head integer
)

view nodes
select tail as node from graph
union
select head as node from graph

select a.node as head, b.node as tail from nodes a, nodes b where distance(a.node, b.node, graph) > 0

Note, that this is purely declarative definition, no inflationary semantics, etc. Received on Tue Oct 21 2003 - 19:22:33 CEST