Re: database design method

Lauri Pietarinen wrote:
>
>OK, I get the picture. But to me it looks like you
>are trying to undermind the original power of the RM
>by somehow introducing new kinds of data dependencies,
>i.e. entities not identified by value but by "position".

No, in fact, that is exactly the problem. If the nodes or subtrees are identified by position then I could easily model it in the flat relational model. But in the examples I gave they are true values and identified by their components.

>What use are my powerfull relational operators if I have to write
>a program to navigate the structure?

All you need is a while-loop or recursion and Tutorial-D has that.

>Anyway, whats so frightening about artificial node identifiers?

Not much, the usual arguments are that they don't have "business meaning" and they make it necessary to add explicit other key constraints to indicate the "real identifier" and in this case you also need extra explicit constraints to indicate that they form a tree. So if we can easily avoid them by extending the data model a little I think we should.

• Jan Hidders