Re: BSR - the Basic Semantic Register

[Martin Bryan <mtbryan@sgml.u-net.com>]

Philip

>   There are 2 scenarios which I would liek to contemplate:
>
>   1. One Product packed in many containers.
>
>         The layout in XML could be as follows
>
>           <Product>
>                 <Container> </Container>
>                 <Container> </Container>
>                 <Container> </Container>
>                  ........
>          </Product>
> 2. Many products in one container
>
>           <Container>
>                  <Product> </Product>
>                  <Product> </Product>
>                  <Product> </Product>
>            </Container>
>
>   The challenge is one cannot predict how a packer will pack a
consignment -
> It will depend on many factors like the size
> of containers, the dimension of product/s etc or just how a particualar
> packer feels on a particular day !!!

Agreed, but then what is the business process? If the process is shipping
then you start from the container that has to be moved. If the process is
ordering you start from the products that have to be packed in the
container. The person ordering does not care how many containers are needed.
The shipper gets to match the orders with the containers.
>
>        There are of couyrse solutions to the above like allowing one OR
"|"
> the other BUT if a hierarchy is expressed in
> sevearal levels the permutations become larger.

XML models have choices defined using OR groups, and choices based on the
use of all of a set of elements without ordering.

> Thus this becomes a
> generalised problem of many to many relationships
> and how to handle them in a hierarchical structure.

Any one instance of a message has a single hierarchy because it has chosen
one of the alternatives, but the model allows for all possible hierarchies.

>        This was a common problem in the 1970's when virtually all DBs were
> Hierarchical. I remember it well.

Those of us with fond memories of Hierarchical DBs are getting rarer by the
day :-)

But do not confuse the hierarchical nature of the message for the need to
store it in a hierarchical database. A good XML database uses XML datatypes
to define the hierarchy, not the XML elements that form the message.
>
>        In general designers tended to flatten the hierarchies as much as
> possible and relate hierarchies thru data fields -
>        and then Ted Codd et al 'invented' the relational Database which is
> the main paradigm today.

>       How does XML deal with many to many ?
>       How will ebXML deal with many to many ?

Through divorcing modelling from instances. Each message has a single
hierarchy that represents a choice from a model that defines the set of
permitted hierarchies.

Martin Bryan