[dsdl-discuss] Selection and Dispatching are different

Part 4, which is now called NVDL (Namespace-based Validation Dispatching Language),
is *not* for selection but for dispatching. The NVDL dispatcher does:

1) create sections from an XML document,
2) combine sections with <attach> and <unwrap>,
3) slightly change combined sections to form validation candidates, and
4) invoke validators for validation candidates

The easiest is 4). Certainly, it should be possible to use Part 10
from 4). I think that the schema attribute of <validate> elements is
good enough for this purpose. We only have to reference to Part 10
schemas (or scripts) with this attribute.

I believe that 2) and 3) are very different from what Martin and Alex
imagine as a selection language. These two steps are the most
difficult part of Part 4. To clarify these steps, I am trying to
provide formal semantics.

Now, it remains to consider 1). This is different from mere
selection, since sections are required to contain slot nodes. If
sections do not contain slot nodes, we cannot apply 2) or 3) to
sections.

At present, 1) uses namespace-based selection (i.e., <namespace
ns="..."> or <anyNamespace>) followed by the introduction of slot
nodes. However, there are no reasons to exclude other selection
mechanisms. In fact, somebody said to me that he wants to create
sections for subtrees rooted by particular elements such as <table>.
This use case requires tag-name-or-attribute-name-based selection. It
might be useful to add this feature before Part 4 becomes an IS.

More sophisticated selection mechanisms (such as XPath) might be
required for creating sections. I think that such an extension should
be done by *borrowing* selection mechanisms from other specs and that
we should not try to stretch Part 4 any further. In other words, I
think that Part 4 should not try to be a selection language, Selection
mechanisms should be detached from Part 4, unless they are extremely
simple.

Cheers,

-- 
MURATA Makoto <murata@hokkaido.email.ne.jp>
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