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Semantics of rdfs:seeAlso (Was: Is it best practices to use a rdfs:seeAlso link to a potentially multimegabyte PDF?)

From: Tim Berners-Lee <timbl@w3.org>
Date: Thu, 13 Jan 2011 06:29:00 -0500
Cc: Nathan Rixham <nathan@webr3.org>, Vasiliy Faronov <vfaronov@gmail.com>, Toby Inkster <tai@g5n.co.uk>, Peter DeVries <pete.devries@gmail.com>, Linked Open Data <public-lod@w3.org>, Dan Brickley <danbri@danbri.org>, Ivan Herman <ivan@w3.org>, Thomas Roessler <tlr@w3.org>
Message-Id: <5C6C3671-6EEB-4D4A-9504-C9E5CE18B9A7@w3.org>
To: Martin Hepp <martin.hepp@ebusiness-unibw.org>

On 2011-01 -13, at 05:10, Martin Hepp wrote:
> I don't buy in to restricting the meaning of "data" in the context of RDF to "RDF data".

You can define "data" however you like for the purpoes of an argument, but with
nothing to do with how rdfs:seeAlso is defined.

> If the subject or object of RDF triples can be any Web resource (information and non-information resource),

That is true.

> then the range of rdfs:seeAlso should also include information resources (i.e., data) of a variety of conceptual and syntactic forms.

That does not follow at all. You just made that up.

It totally depends on the semantics we define for rdfs:seeAlso.
Now, we could define many things, but the older FOAF practice has encouraged many people to use it as part 
a protocol in which the writer writes
		<#i> foaf:knows   [ foaf:name "Fred"; foaf:personalMailbox mailto:fred@acme.org;   rdfs:seeAlso <http://acme.org/people/fred>.

and the reader follows the see:Also, gets RDF and and does smushing.
I referred to that in the LinkedData note.

> And PDF, HTML without RDFa as well as images clearly qualify as data.

The protocol deployed in FOAF and linked data clients requires it to be RDF.

We can push the community either way, but either we have to use rdfs:seeAlso in that way or we have to push a lot of people
to change their fFOAF-generators and their FOAF-crawlers and their LOD-client libraries to stop following those links.

> They are also clearly machine-accessible. If you are still not convinced: What about CSV files or text files containing ACE (controlled English), or OData / GData?

Those do not wok in the protocol.  FOAF crawlers and tabulator wlll not use them to make a vast web of data as they do currently when they use RDF.

> By the way, the problem of having to load huge amounts of data following rdfs:seeAlso is not limited to PDFs - even obeying Tim's proposal means there could be huge RDF graphs linked to via rdfs:seeAlso, and that is of course conceptually perfectly okay.

Conceptually perfectly OK is one thing, of course. But that doesn't give us practically perfectly OK.
This is a practical engineering exercise, building LOD protocols which work.

> After all, rdfs:seeAlso is not rdfs:linkToASmallChunkOfVeryRelatedDateInRDF ;-)

The words in the URI of course have no semantics themselves, as you know. They
are only mnemonics.

> Data management and data quality heuristics should not be solved at the conceptual level. If old clients employ outdated heuristics, those clients should update their heuristics, IMO.

This is the Linked Open Data list.
The Linked Data world is a well-defined bit of engineering.
It has co-opted the rdf:seeAlso semantics of "if you are looking up x load y" from the much 
earlier FOAF work.  This protocol is heavily used in code and data out there.

The URI space is full of empty space waiting for you to define terms
with whatever semantics you like for your own use.
But one cant argue philosophically that for some reason 
the URI rdfs:seeAlso should have some other meaning when people are using it and 
there have been specs.

One *can* argue that the RDFS spec is definitive, and it is very loose in its definition.
We could look at maybe asking for an erratum to the spec
to make it clear and introduce the other term int the same spec.
But if the result is to make rdf:seeAlso the general term which cannot be automated
then we have to be aware that there is a bunch of code to be changed.


> Best
> Martin
> On 12.01.2011, at 16:13, Nathan wrote:
>> Hi Martin,
>> Martin Hepp wrote:
>>> For my taste, using rdfs:seeAlso is perfectly valid (yet suboptimal, because too unspecific), according to the RDFS spec:
>>> http://www.w3.org/TR/rdf-schema/#ch_seealso
>>> Quote: "rdfs:seeAlso is an instance of rdf:Property that is used to indicate a resource that might provide    additional information about the subject resource.
>>> A triple of the form:
>>> S rdfs:seeAlso O
>>> states that the resource O may provide additional information about S. It may be possible to retrieve representations of O from the Web, but this is not required. When such representations may be retrieved, ***no constraints are placed on the format of those representations***."
>> Generally it appears to me that rdfs:seeAlso is a property for a machine to follow in order to get more information, and that much of the usage mentioned in this thread requires a property which informs a human that they may want to check resource O for more information - essentially something similar to a hyperlink in a html document with no @rel value.
>> Best,
>> Nathan
Received on Thursday, 13 January 2011 11:29:09 UTC

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