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DC-ARCHITECTURE  February 2012

DC-ARCHITECTURE February 2012

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Subject:

Re: DCAM: the analogy to SKOS

From:

Pete Johnston <[log in to unmask]>

Reply-To:

DCMI Architecture Forum <[log in to unmask]>

Date:

Wed, 1 Feb 2012 17:38:45 +0000

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Hi all,

I'm a bit (OK, very!) confused about this analogy between DCAM and SKOS.

To me, SKOS has two components:

- a model of (a part of) the "world" as made up of concepts, concept schemes, lexical terms etc, which have certain attributes and certain relationships between them
- an RDF vocabulary (or two if you distinguish base SKOS and SKOS-XL) for use in creating RDF graphs/triples to describe that "world"

SKOS is quite generalised so it can condition how we choose to model our "worlds" in other domains (e.g. do I model my "places" as SKOS Concepts with broader/narrower relations or as spatial things with contains/is-contained-by relations? And so on)

But using SKOS doesn't determine/change the nature of my data structures, or the "lens" I apply to those data structures; it only changes my "world" structures: using SKOS I'm still squarely within the framework of RDF graph and triple data structures. SKOS Concept Schemes and Concepts are just more "things" in the "world", but in terms of how my data about those things is "packaged", SKOS Concept Schemes and Concepts are treated exactly the same as any other thing (a foaf:Person, a bibo:Document, a dcmitype:Collection etc etc etc).

But - with its notions of Description Set, Description and Statement - DCAM does introduce new data structures, or at least (as I prefer to try to think of it) a new "lens on", a new way of looking at and referring to parts of, the RDF graph/triple structure. 

In contrast to SKOS, with DCAM, it's not a question of looking at "the world" in a different way. Whether I think of my data as an RDF graph or a DCAM Description Set (or as both, depending on how I'm looking at it!), my "world" is still the same: it has foaf:Persons who author bibo:Documents that are about skos:Concepts that are in skos:ConceptSchemes. 

Rather with DCAM, I'm looking at the structure of my _data_ in a different way. 

So I'm afraid I'm struggling to grasp the significance of comparing the DCAM to SKOS - at least at the level that comparison seems to be being applied in these discussions. I understood Andy's mention of SKOS on 05/01 

https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=DC-ARCHITECTURE;dc1738b9.1201

to be about the practical usefulness of SKOS, the fact that it addresses a requirement that people have ("how do I represent my thesaurus using RDF?"), not saying that DCAM was something "similar in nature" to SKOS.

Further on in that thread, Kai said on 09/01:

https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=DC-ARCHITECTURE;1fc1d387.1201

> RDF is not only defined for the representation
> of metadata, it is so abstract that at the same time, it allows for instance the
> definition of ConceptSchemes in SKOS. And if there is a need for the
> definition of a ConceptScheme, I argue that there is a need for the definition
> of a DescriptionSet, too.

I think this is where I got lost :)

(To me), a SKOS Concept Scheme is just another thing in my "world" (alongside a FOAF person etc), another thing to be named with a URI and described in my data, my graph, using RDF triples. 

But a DCAM Description Set is "a thing in my data", not in my "world". Sure, I could name and describe it (just as I could name and describe an RDF graph or an RDF triple) but my main "use" of the Description Set notion is as a way of structuring my data.

So, from my perspective, I can't help feeling that an SKOS Concept Scheme and a DCAM Description Set are very different things, and I'm struggling to grasp why comparing them is useful. 

I'm not saying it isn't useful, just that, right now, I don't "get it" :)

Pete

Pete Johnston
Technical Researcher
Eduserv
E: [log in to unmask]
T: +44 (0)1225 474323
F: +44 (0)1225 474301
www.eduserv.org.uk
Eduserv is a company limited by guarantee (registered in England & Wales, company number: 3763109) and a charity (charity number 1079456), whose registered office is at Royal Mead, Railway Place, Bath, BA1 1SR.


> -----Original Message-----
> From: DCMI Architecture Forum [mailto:DC-
> [log in to unmask]] On Behalf Of Thomas Baker
> Sent: 26 January 2012 23:31
> To: [log in to unmask]
> Subject: DCAM: the analogy to SKOS
> 
> In yesterday's Provenance Task Group telecon we found ourselves talking
> about DCAM [1].  One point of discussion was the analogy of DCAM to SKOS.
> 
> On January 5, Andy had written:
> 
> > So I think the pertinent question that needs to be answered pretty
> > early on in the outer layers of Stuart's onion is "why should I invest
> > time understanding the DCAM when I could be learning RDF/Linked
> Data/whatever instead?".
> >
> > If we compare the DCAM with, say, SKOS and ask the same kind of
> > question the answer is more obvious I think - people need to
> > understand both RDF and SKOS because SKOS gives them something useful
> > in the area of 'vocabulary' handling that RDF on its own doesn't give them.
> >
> > The answer for the DCAM is much less clear except in terms of the
> > original rationale for having the DCAM at all, i.e.
> >
> > "It provides an information model which is independent of any
> > particular [DCMI] encoding syntax. Such an information model allows us
> > to gain a better understanding of the kinds of [DCMI] descriptions
> > that we are encoding and facilitates the development of better mappings
> and cross-syntax translations"
> > ("[DCMI]" additions by me).
> >
> > which, unfortunately, is a very inward looking (and rather narrow)
> > rationale that is unlikely (as history has shown us) to be of much
> widespread interest.
> 
> To which Kai had responded:
> 
> > [The] analogy to SKOS is perfect, because that was exactly how I
> > started the RDF-based DCAM wiki page yesterday [1].
> > Provide DCAM as a model for metadata just like SKOS is for vocabulary
> > handling.
> >
> > [1] http://wiki.dublincore.org/index.php/DCAM_Revision_Tech
> 
> In yesterday's call, Kai elaborated on the notion of DCAM as an equivalent of
> SKOS for metadata.  I understood him to say that SKOS is an RDF vocabulary,
> but one might also see it as an Abstract Model that could be used by people
> who do not care about RDF.
> 
> This reminded me that in the Semantic Web Deployment WG, we did in
> effect try to express a high-level "abstract model" for SKOS (a formulation I
> actually helped write) [2]:
> 
>     Using SKOS, _concepts_ can be identified using URIs, _labeled_ with lexical
>     strings in one or more natural languages, assigned _notations_ (lexical
>     codes), _documented_ with various types of note, _linked to other
> concepts_
>     and organized into informal hierarchies and association networks,
>     aggregated into _concept schemes_, grouped into labeled and/or ordered
>     _collections_, and _mapped_ to concepts in other schemes.
> 
> ...summarizing the essence of SKOS in just one sentence.  Arguably, this is
> the sort of formulation -- one which does not itself even mention RDF but
> which maps to RDF in the specification -- we could aspire to make for DCAM.
> 
> I cannot readily formulate one sentence that summarizes what I think DCAM
> can offer, though it would perhaps be interesting to try.  The story I have in
> mind for DCAM might say that metadata uses items of information -- strings
> and URIs, perhaps belonging to sets of strings or URIs (i.e., syntax or
> vocabulary encoding schemes) -- to describe (make statements about) things
> of interest; that it groups these items into Descriptions about one particular
> thing of interest and groups related Descriptions into Description Sets, which
> are often instantiated in implementations as "records".
> 
> How these items are used to make meaningful "statements" about things
> would be the part that one inherits from RDF.  DCAM, as I see it, can provide
> an "interface" to underlying (meaningful) statements by specifying patterns
> of information items grouped into Descriptions and Description Sets.
> 
> If that is what DCAM is, or should be, then I wonder whether we can specify
> those patterns in enough detail to be useful as an interface to triples without
> becoming too complicated.  In 2007-2008, for example, it seemed reasonable
> to translate "DCAM statements" about value resources using RDF statements
> with rdf:value and literals or RDF statements with dcam:memberOf and
> vocabulary encoding scheme URIs [3].  From the perspective of best practice,
> that looks like an oversimplification.  Today, one might want to consider using
> various other properties in statements about a value resource -- rdfs:label,
> skos:prefLabel, skos:notation, foaf:name, or dcterms:title... -- though
> perhaps _not_ rdf:value [4].  Can a DCAM still be defined as an interface to
> triples as straightforward as [4], or would it need to evolve in the direction of
> a more complex and differentiated set of patterns?
> 
> For discussion on Monday's call (at 11:00 EST)...
> 
> Tom
> 
> [1] http://wiki.bib.uni-mannheim.de/dc-
> provenance/doku.php?id=minutes_2012_01_15
> [2] http://www.w3.org/TR/skos-reference/
> [3] http://dublincore.org/documents/dc-rdf/#sect-4
> [4] http://www.w3.org/2011/rdf-wg/track/issues/27
> 
> --
> Tom Baker <[log in to unmask]>

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