I've been thinking a lot about the graph model question, and have been
doodling in Inkscape as a way of thinking about this.
Attached find three pictures, in editable (svg) and non-editable (png)
versions.
There's a graphical reflection of my comment about the semantics of
our graphs: "Evaluation of a subpipeline evaluates every component in
it exactly once, and a document (sequence) flows down every (grey)
pipe in it exactly once". Dotted lines are magic -- they have
different semantics depending on the kind of construct they're in.
fig2 is a careful version of Figure 2 from the WD. The dotted lines
are contingent, that is, they may or may not see data flow.
fig1a is a simple for-each example, taking Figure 1 in the WD and
embedding it in a for-each. Here the top dotted line iterates over
all the docs in the sequence input to the for-each, and the bottom
dotted line assembles the single outputs of each evaluation of the
XInclude/Valide subpipeline and outputs them as a document sequence on
the for-each output.
fig1b is the one I find most interesting -- the new (left hand) dotted
line _repeatedly_ flows its input to the 'schema' port of the Validate
step. The other two are as for fig1a.
ht
--
Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
Half-time member of W3C Team
2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
URL: http://www.ltg.ed.ac.uk/~ht/
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