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Re: ISSUE-186: Last Call Comment: Mappings

From: Alistair Miles <alistair.miles@zoo.ox.ac.uk>
Date: Wed, 22 Oct 2008 10:40:00 +0100
To: public-swd-wg@w3.org
Cc: public-esw-thes@w3.org
Message-ID: <20081022093958.GA9340@skiathos>

Hi all,

At yesterday's telecon Guus took an action to respond to this
comment. Here are a few notes of my own based on comment I made
yesterday.

On Wed, Oct 08, 2008 at 10:09:25AM +0000, SWD Issue Tracker wrote:
> 
> 
> ISSUE-186: Last Call Comment: Mappings
> 
> http://www.w3.org/2006/07/SWD/track/issues/186
> 
> Raised by: Sean Bechhofer
> On product: SKOS
> 
> Raised by Michael Panzer [1]:
> 
> 6. Mappings
> -----------
> 
> The problem of restricting SKOS to one-to-one mappings has already been
> raised as ISSUE-131. We share the concerns expressed there.
> 
> We also see potential problems in deriving the mapping relations
> skos:broadMatch and skos:narrowMatch from skos:broader and
> skos:narrower. In ISO standard and current practices many multilingual
> thesauri did not use broader or narrower to indicate the mapping
> relations. SKOS should revisit those standards and follow the current
> standards' development to make sure SKOS is consistent in representing
> the indicators used by standards (and the thesauri following those
> standards) for so many years.  

The SKOS mapping properties have their roots in ISO 5964 and have been
informed more recently by BS 8723 part 4.

I don't have ISO 5964 to hand so I may not quote precisely from it
here, hopefully others can correct me if I make any glaring errors.

ISO 5964 introduced the notions of exact, inexact and partial
correspondance between thesaurus descriptors. These provided
inspiration for the SWAD-Europe report on inter-thesaurus mapping,
which first described the use of the SKOS Mapping RDF schema [1].

Note in particular that the "partial" correspondance as described in
ISO 5964 indicated that the meaning of one descriptor *either*
subsumes *or* is subsumed by the meaning of the other. Hence [1]
refined the notion of a partial mapping to provide broad and narrow
mapping properties, which are clearly more useful than the ambiguous
"partial". We felt this was consistent with the intention of ISO 5964
(see also note [2]).

BS 8723 part 4 ("interoperability between vocabularies") provides a
clear (IMO) discussion of mapping between extant vocabularies. It
illustrates the use of standard hierarchical and associative
relationships (BT, NT and RT), in addition to an equivalence (EQ)
relationship, to assert mappings between vocabularies, in what they
call "differentiated mappings". These directly correspond to the
skos:broadMatch, skos:narrowMatch, skos:relatedMatch and
skos:exactMatch properties. (See also note [3].)

We realise that "undifferentiated mappings" (where the nature of the
correspondance is not specified) may represent the majority of real
world mapping data. However, "differentiated mappings" are also an
important resource, and are being constructed at scale e.g. by FAO.

Hence the current design for SKOS is based on a perceived consensus
for mapping between vocabularies, which is to ground the different
types of mapping relationship in the notions of hierarchical and
associative relationships, and we believe that this consensus is
consistent with existing standards.

Cheers,

Alistair.

[1] http://www.w3.org/2001/sw/Europe/reports/thes/8.4/ 

[2] IMO ISO 5964 requires careful interpretation. From previous
readings, I understood that ISO 5964 is primarily aimed at describing
the *process* of constructing a single multilingual thesaurus, *not*
on mapping between extant monolingual thesauri in either the same or
different languages. The notions of "exact", "inexact" and "partial"
are used to describe the types of correspondance that can be
encountered between different language components *during the process
of constructing a multilingual thesaurus*, with the implication being
that anything other than an exact correspondance must usually be more
closely aligned before the thesaurus is finally published.

[3] Although the main body of BS 8723-4 discusses mapping between
vocabularies (sections 5-8), where the assumption is that
modifications to each vocabulary cannot be made to improve the
alignment, BS8723-5 also discusses the process of constructing a
single multilingual thesaurus (section 9), where changes can be made
to each language component to improve the overall alignment of the
thesaurus. IMO section 9, whilst valuable, is out of place in
BS8723-4, because the process of constructing a single multilingual
thesaurus (where language components can be modified to improve
alignment) is different from the process of mapping between extant
thesauri (where mappings have to describe aligment as-is), and would
be better treated in a separate document.

-- 
Alistair Miles
Senior Computing Officer
Image Bioinformatics Research Group
Department of Zoology
The Tinbergen Building
University of Oxford
South Parks Road
Oxford
OX1 3PS
United Kingdom
Web: http://purl.org/net/aliman
Email: alistair.miles@zoo.ox.ac.uk
Tel: +44 (0)1865 281993
Received on Wednesday, 22 October 2008 09:40:41 GMT

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