LISTSERV mailing list manager LISTSERV 16.5

Help for CODE4LIB Archives


CODE4LIB Archives

CODE4LIB Archives


CODE4LIB@LISTS.CLIR.ORG


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

CODE4LIB Home

CODE4LIB Home

CODE4LIB  September 2013

CODE4LIB September 2013

Subject:

Re: Expressing negatives and similar in RDF

From:

Karen Coyle <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Tue, 17 Sep 2013 09:54:33 -0700

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (94 lines)

Agreed that SPARQL is ugly, and there was  discussion at the RDF 
validation workshop about the need for friendly interfaces that then 
create the appropriate SPARQL queries in the background. This shouldn't 
be surprising, since most business systems do not require users to write 
raw SQL or even anything resembling code - often users fill in a form 
with data that is turned into code.

But it really is a mistake to see OWL as a constraint language in the 
sense of validation. An ontology cannot constrain; OWL is solely 
*descriptive* not *prescriptive.* [1]

Inferencing is very different from validation, and this is an area where 
the initial RDF documentation was (IMO) quite unclear. The OWL 2 
documents are better, but everyone admits that it's still an area of 
confusion. (In a major act of confession at the DC2013 meeting, Ivan 
Herman, head of the W3C semantic web work, said that this was a mistake 
that he himself made for many years. Fortunately, he now helps write the 
documentation, and it's good that he has that perspective.) In effect, 
inferencing is the *opposite* of constraining. Inferencing is:

"All men are liars. Socrates is a man. Therefore Socrates is a liar."
"Every child has a parent. Johnny is a child. Therefore, Johnny has a 
parent." (whether you can find one or not is irrelevant)
"Every child has two parents. Johnny is a child. Therefore Johnny has 
two parents. Mary is Johnny's parent." (no contradiction here, we just 
don't know who the other parent is)
"Every child has two parents. Johnny is a child. Therefore Johnny has 
two parents. Mary is Johnny's parent. Jane is Johnny's parent. Fred is 
Johnny's parent." Here the reasoner detects a contradiction.

The issue of dct:titles is an interesting example. dct:title takes a 
literal value. If you create a dct:title with:

X dct:title http://example.com/junk

with OWL rules that is NOT wrong. It simply provides the inference that 
"http://example.com/junk" is a string - but it can't prevent you from 
creating that triple, because it only operates on existing data.

If you say that every resource MUST have a dct:title, then if you come 
across a resource without a dct:title that is NOT wrong. The reasoner 
would conclude that there is a dct:title somewhere because that's the 
rule.  (This is where the Open World comes in) When data contradicts 
reasoners, they can't work correctly, but they act on existing data, 
they do not modify or correct data.

I'm thinking that OWL and constraints would be an ideal training 
webinar, and I think I know who could do it!

kc

[1] http://www.w3.org/TR/2012/REC-owl2-primer-20121211/
"OWL 2 is not a schema language for syntax conformance. Unlike XML, OWL 
2 does not provide elaborate means to prescribe how a document should be 
structured syntactically. In particular, there is no way to enforce that 
a certain piece of information (like the social security number of a 
person) has to be syntactically present. This should be kept in mind as 
OWL has some features that a user might misinterpret this way. "


On 9/17/13 4:50 AM, [log in to unmask] wrote:
> I don't think anyone would want to use one ontology for all work, especially not a public ontology. I can imagine people using ontology extensions that are specific to the purpose of validation, and I've found them useful myself.
>
> I'm not arguing against using SPARQL for validation. I do think that OWL offers a more natural-feeling language for discussing constraint for most folks, and I suppose that's why we've seen the introduction of extension languages like SPIN to intermediate a little between the user and plain SPARQL.
>
> ---
> A. Soroka
> The University of Virginia Library
>
> On Sep 16, 2013, at 11:00 PM, CODE4LIB automatic digest system wrote:
>
>> From: Karen Coyle <[log in to unmask]>
>> Date: September 16, 2013 10:22:47 AM EDT
>> Subject: Re: CODE4LIB Digest - 12 Sep 2013 to 13 Sep 2013 (#2013-237)
>>
>>
>> On 9/16/13 6:29 AM, [log in to unmask] wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> I'd suggest that perhaps the confusion arises because "This instance is (not) 'valid' according to that ontology." might be inferred from an instance and an ontology (under certain conditions), and that's the soul of what we're asking when we define constraints on the data. Perhaps OWL can be used to express conditions of validity, as long as we represent the quality "valid" for use in inferences.
>> Based on the results of the RDF Validation workshop [1], validation is being expressed today as SPARQL rules. If you express the rules in OWL then unfortunately you affect downstream re-use of your ontology, and that can create a mess for inferencing and can add a burden onto any reasoners, which are supposed to apply the OWL declarations.
>>
>> One participant at the workshop demonstrated a system that used the OWL "constraints" as constraints, but only in a closed system. I think that the use of SPARQL is superior because it does not affect the semantics of the classes and properties, only the instance data, and that means that the same properties can be validated differently for different applications or under different contexts. As an example, one community may wish to say that their metadata can have one and only one dc:title, while others may allow more than one. You do not want to constrain dc:title throughout the Web, only your own use of it. (Tom Baker and I presented a solution to this on the second day as Application Profiles [2], as defined by the DC community).
>>
>> kc
>> [1] https://www.w3.org/2012/12/rdf-val/agenda
>> [2] http://www.w3.org/2001/sw/wiki/images/e/ef/Baker-dc-abstract-model-revised.pdf

-- 
Karen Coyle
[log in to unmask] http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

March 2024
February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
July 2022
June 2022
May 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
September 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004
July 2004
June 2004
May 2004
April 2004
March 2004
February 2004
January 2004
December 2003
November 2003

ATOM RSS1 RSS2



LISTS.CLIR.ORG

CataList Email List Search Powered by the LISTSERV Email List Manager