XSchema: Namespace PIs in XSchemas considered harmful
cowan at locke.ccil.org
Tue Jul 7 21:43:58 BST 1998
I believe that the emerging consensus for using namespace PIs,
with or without XSC:Namespace elements, to identify the
prefixes of element/attribute names being described by the XSchema
is a Bad Thing. Namespace PIs, on the other hand, are necessary
for defining the XSchema prefix (nominally "XSC:") and for identifying
prefixes in metadata elements physically within the XSchema.
The trouble comes when the same namespace is referred to in both
places but with a different prefix. For instance, suppose we
have an XSchema defining SomeML. The prefix used in SomeML documents
is "SML:", and a namespace PI (with or without an XSC:Namespace
element) is used to define this.
However, the XSchema may also wish to have metadata elements drawn
from other sources. If the XSchema draws from SimpleML and uses
the same prefix "SML:" for it, there is a conflict between using
the "SML:" prefix and mentioning it.
I propose, therefore, that namespace PIs be reserved for the use
of prefixes (in element names and attributes) in XSchemas, and
XSC:Namespace elements be used as the sole indicators of mentioned
prefixes (in declarations of element names and attributes).
John Cowan http://www.ccil.org/~cowan cowan at ccil.org
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