Re: Substitution groups and Parsing Efficiency

Mark Feblowitz <mfeblowitz@frictionless.com> writes:

> While (ab)using a particular substitution group, I noticed in the XSV error
> report that the fsm for the substitution group was huge.
> 
> The substitution group is indeed large (many possible substitutions), and is
> referenced in many places, with a cardinality of 0..unbounded. This means
> that any number of the substitutions could appear any number of times, and
> in any order. This, indeed, would lead to a large fsm - in fact to an "nfsm"
> (with a non-finite set of potential states).
>
> My question is, do schema validators typically have efficient algorithms for
> handling such cases? How about cases that are finite but large?

The REC mandates that a substitution group head be treated as a
disjunction over its members.  It follows that a 0..unbounded s-g head
is no different than a 0..unbounded xs:choice of all its members.  The
fsm fragment for such a choice is straight-forward, and certainly
never infinite.  The UPA guarantees that there are no unbounded
multiplicative effects of having several such fragments in the overall
fsm for a content model: at worst every edge following such a fragment
has to be duplicated once.  For example the regexp corresponding to
the determinised fsm for (a|b)*(c|d)*e is (a|b)*(e|((c|d)(c|d)*e)).

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
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Received on Tuesday, 8 January 2002 04:03:15 UTC