[developers] LKB vs. PET divergences

[Melanie Siegel]

Hi,
I've moved the definitions to the rule types (and let the instance 
inherit from one type only), and it looks right now. It's in CVS.

Melanie

Stephan Oepen wrote:

> hi again,
> 
> francis is still visiting, cracking the whip.  so we sat down to debug
> an unpleasant problem: the LKB and PET producing different results for
> some inputs.  after many hours staring at feature structures, it seems
> the problem originates in different `interpretations' of one rule from
> the grammar, viz. the `vstem-vstem-rule'.  i attach the AVMs for just
> the rule below (`dag.lkb' vs. `dag.pet'), so you will quickly see that
> the LKB has
> 
>   [ SYNSEM.LOCAL.CONT.HOOK #0, C-CONT.HOOK #0 ]
>   --> [ ], [ SYNSEM.LOCAL.CONT.HOOK #0 ]
> 
> whereas PET lacks the coreference with the HOOK of the second daughter.
> this would explain why PET sometimes finds additional derivations, i.e.
> ones that later fail to re-build in the LKB when treebanking.
> 
> looking at the definition of this rule in `japgram.tdl' and walking up
> the type hierarchy a little, we fail to see why the coreference should
> be there (the one to the second daughter, that is).  but given general
> exhaustion and the power of well-formed unification, we feel not quite
> certain of our analysis (having to assume that either the LKB or PET
> could be incorrect was hard enough :-).
> 
> hence, we are hoping experts in the grammar or formalism could give it
> a critical look over-night?  i attach the full grammar and the two DAG
> representations for the rule.  how many re-entrancies for HOOK should
> we expect to see in a fully expanded, well-formed `vstem-vstem-rule'?
> 
> looking at the definition of the rule, i also noticed it uses multiple
> supertypes in the instance definition.  this is generally illegal, but
> happens to succeed in this case, because for:
> 
>   vstem-vstem-rule := head-final-type & orth-princ & [...]
> 
> there appears to be a glb in the type hierarchy.  both systems seem to
> compile the above without complaint, but i believe the above situation
> should be flagged or outright rejected as syntactically ill-formed.
> 
>                                                        cheers  -  oe
> 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +++ Universitetet i Oslo (ILF); Boks 1102 Blindern; 0317 Oslo; (+47) 2285 7989
> +++     CSLI Stanford; Ventura Hall; Stanford, CA 94305; (+1 650) 723 0515
> +++       --- oe at csli.stanford.edu; oe at hf.uio.no; stephan at oepen.net ---
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

-- 
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Dr. Melanie Siegel	siegel at dfki.de
DFKI GmbH		Tel: (+49 681) 302-5288
Stuhlsatzenhausweg 3	Fax: (+49 681) 302-5338
D-66123 Saarbruecken	http://www.dfki.de/~siegel/
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