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W. E. Perry scripsit:
> Indeed they do, but in my opinion they should be basing those decisions on the data
> instances which they have actually got rather than upon some authority which purports to
> govern such instances. (This gulf between revelatio and auctoritas is certainly nothing
> new).
The trouble with "the data instances which they have actually got" is that
they may represent an undersample of the actual data to be received during
the life of the application. An application driven by input data is in
the position of a judge attempting to interpret a statute: any available
information on authorial intent is valuable.
Fundamentally, validation serves one of two purposes: self-consistency and
suitability. Classic DTDs were designed to provide self-consistency (an
instance respects the constraints it says it respects) and have nothing to
do with suitability. However, it is also possible to use schemas
(including DTDs) as suitability testers, and this is the explicit use model
of RELAX NG. Here a receiver expresses declaratively a set of constraints
that would otherwise have to be programmed into its code that restrict the
sort of input it is willing to deal with. Depending on the overall system,
rejected input can be sent down a channel or just dropped.
This leads to the notion of a Linda system in which one accepts XML documents
from the Lindasphere based on a RELAX NG schema: documents which match the
application-provided schema are read (and typically, but not necessarily),
removed; other documents persist until some other reader accepts them.
--
John Cowan jcowan@reutershealth.com
At times of peril or dubitation, http://www.ccil.org/~cowan
Perform swift circular ambulation, http://www.reutershealth.com
With loud and high-pitched ululation.
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