Re: Re: From TODO, XML?

mlw <markw(at)mohawksoft(dot)com> wrote:

> "Frank Ch. Eigler" wrote:
> > : So a parser that can scan a DTD and make a usable create table (...)
> > : line would be very helpful. [...]
> >
> > Hmm, but hierarchically structured documents such as XML don't map
> > well to a relational model. The former tend to be recursive (e.g.,
> > have more levels of containment than the one or two that might be
> > mappable to tables and columns.)
>
> Yes!!! Exactly, being able to understand the recursive nature of XML and
create
> relations on the fly would be a very cool feature.

I think there is a pretty straight forward mapping, except for one possible
ambiguity.

If an element, say <address>, is contained within another element, say
<employee>, it could either be a column (or group of columns) in an Employee
table, or it could be a table Address which references Employee.

When you say "create relations on the fly", what exactly do you mean? I can
see it would be handy to have CREATE TABLE statements written for you, but
it seems likely that a human would want to edit them before the tables are
actually created. You cannot infer much type information from the DTD. I
don't think there's a way to infer a primary key from a DTD, so you would
want to either specify one or add a serial column (or perhaps that would
always be done automatically). An XML schema would have more information,
of course.