With the recommondation of the xschema by the w3c in may 2001, xml instances now provide a lot more opportunities for semantic data checks.
Now it is possible to defines elements and attributes with certain data-types like date, time, long, 6 character string, list of values etc. etc.
This approach is a big step forward in particular for the exchange of engineering data. They consits often of non human readable information which have to be used in several tool chains and processes, which require strict data typing.
But there is still a lack of functionality!
Every constraints relate on a fixed strucuture. But what happen, if the structure itself (including list of values, attribute lists, mandatory elements...) changes by e.g. the maturity level of a information.
This will happen in the life-cycle of a document like a processing guide: If a document becames valid, a signature of a member of a specific group is mandatory, but not in the first initial draft phase.
Another usecase is e.g. in the manufacture/supplier relationship.
It is very useful, to have basic structure definitions (in a dtd or schema...) for exchanging information, but in addition to that every company may have different value lists for team-members, maturity levels due to internal policies or database related value lists for variable names.
To avoid now to develop and spread a bunch of DTD's for every company and for every process step the DCI approach allows the customization of a DTD to specific needs and support basic aggreements of the data-structures.
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