Storing Lots of Fiddly Bits (was Re: What is XML for?)

[Mark Birbeck]

I know this thread has progressed but one of the original points has not
been addressed so I'd like to re-raise it.

W. Eliot Kimber wrote on 30 January 1999 00:49
> But, the XML data model, that is, the abstract model for the
> *serialization* is not the same as the abstract model of the 
> data being
> serialized.

[and]

> Here is one possible (of an infinite number of possible) XML 
> serialization:
> 
> <?xml version="1.0"?>
> <data-serialization>
> <schema-ref>business objects schema</schema-ref>
> <data-instances>
> <entity-instance id="i0000">
>  <types>
>   <type>person</type>
>   <attributes>
>    <attribute>
>     <attname>name</attname>
>     <attvalue>Eliot</attvalue>
>    </attribute>
[etc.]

[and]

> You get the idea--clearly the in-memory abstraction of the 
> document bears
> no direct relationship to the in-memory abstraction of the 
> original data.

All this is true, but I wonder if you are not comparing like with like.
The model for your data should be more like:

<person oid="1">
  <name>Eliot</name>
  <sex>male</sex>
  <employer oid-ref="2" />
</person>

<enterprise oid="2">
  <name>ISOGEN International Corp</name>
  <address>Dallas, TX</address>
  <derived obj="employs" oid-ref="1" />
</enterprise>

Although you are right to say there are 'an infinite number' of possible
mappings, if you use a representation that relies on a completely
different DTD to represent the data, you shouldn't then be surprised if
your XML no longer mirrors that original data. Nothing says my mapping
is right, but at least it is based on the same schema that you
introduced at the beginning of your message, namely:

> TYPE gender ENUM;
>   male;
>   female;
>   unknown;
> END_TYPE:

> ENTITY person SUBTYPE OF being;
>   name : STRING;
>   sex  : gender;
>   employer : OPTIONAL enterprise;
> END_ENTITY;
[etc.]

I think, if we are to use object databases - and of course the jury is
still out - the issue is how do we import and export XML files, using
the relevant DTD to control the process. This is different to importing
and exporting using a 'serialisation DTD', which expresses nothing but
meta-data - not the original data.

Mark Birbeck
Managing Director
Intra Extra Digital Ltd.
39 Whitfield Street
London
W1P 5RE
w: http://www.iedigital.net/
t: 0171 681 4135
e: Mark.Birbeck at iedigital.net

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