Re: Proposed change to the charter, section 4. Deliverables, Recommendation Track

Dear Holger,

I am not experienced in W3C procedures and didn't phrase it correctly so
I'll try it again.

I think what you suggested is rushing into something without all the
options on the table.
(disclaimer: I would be in favor of a Shapes-like / SPIN-like / CWA OWL
option)

Since the announcement of ShEx, almost everybody rushed into rejecting ShEx
as it is not appropriate for validation and proposed their existing options.
For me Shapes contains many semantics that many people in this list
(including TopQuadrad) rejected already, yet I see now you proposing Shapes
as an option.

What I suggested was taking one step back and see all the options in
action.
- Not everyone is expert in all technologies so a general overview is
needed before defining the requirements
- The issue example that everyone uses is wear-off and not very helpful
- This list is full of disperse example snippets

Using PROV as a use case has many advantages
- We can compare options in the exact same context
- There are many real-world datasets that can be used as validation input
- All efforts will be coordinated from now on and (hopefully) comments will
target actual use cases
- As I said, PROV constraints have some moderate complexity
- The work done here will also benefit the prov community

An expert of each validation language could easily transform all
constraints very fast (less than a day) and we could use a website (even
purl.org/net/rdf-validation) where we post validation snippets for each
constraint.
Thus, with a couple of days work max in total, all the discussions will be
more constructive.

Please correct me if I am completely wrong or completely off-topic here.

Best,
Dimitris




On Sun, Aug 3, 2014 at 12:29 PM, Holger Knublauch <holger@topquadrant.com>
wrote:

>  Hi Dimitris,
>
> yes such exercises are important and should be done at some stage. I guess
> the actual WG could tackle those. This discussion thread here is all about
> the charter so that we can start a WG in the foreseeable future. I
> therefore believe you may want to open a separate email thread for your
> specific proposal. I don't understand your "it would be more interesting".
>
> I am sure there are other, similar example scenarios, including the SKOS
> Integrity Constraints [1] and the hundreds of use cases to be collected by
> the requirements task force. It is fairly obvious to me that no single
> approach will be the ideal choice for all of them, which is why I believe
> that a combination of
>
> 1) SPIN (to bring in the flexibility of SPARQL, and as a meta-language for
> 2)
> 2) A Shapes vocabulary (as a collection of frequently needed constraints
> that is easy-to-use)
> 3) OWL Closed World (for existing ontologies and OWL compliance)
>
> will be our safest bet to satisfy most requirements. The list above
> outlines the three mandatory deliverables that I would like to see.
>
> Regards,
> Holger
>
> [1] http://www.w3.org/2001/sw/wiki/SKOS/Validation
>
>
>
> On 8/3/2014 18:30, Dimitris Kontokostas wrote:
>
>
>
>
> On Sun, Aug 3, 2014 at 9:21 AM, Holger Knublauch <holger@topquadrant.com>
> wrote:
>
>> A pragmatic proposal: I do believe there is consensus that this WG can
>> potentially create some useful and relevant output that could lead to
>> broader use cases for semantic web technology as a whole. There are several
>> proposals on the table that are potentially complementary to each other.
>> Assuming there are enough people who actually sign up for the work, why not
>> produce multiple deliverables that cover more use cases?
>>
>> 1) Shapes + SPIN, with an explicit mandate to have semantics that are
>> executable by SPARQL engines, from day one. The alternative would be ShEx
>> and this could be figured out in the beginning of the WG. This deliverable
>> would be like an extension to SPARQL.
>>
>> plus
>>
>> 2) OWL closed world semantics, so that existing OWL ontologies can be
>> reused. This deliverable would basically be an "appendix" to the OWL 2 spec.
>>
>> This would allow the interest groups to stay on their home turf without
>> blocking each other, because blocking each other would be the worst outcome
>> of all. I see no technical difficulties with such as stack, because these
>> technologies are complementary to each other: we use OWL closed world +
>> SPIN all the time, and it works well in practice. In fact I believe both
>> specifications have a good and stable starting point so that we could
>> proceed with the process very swiftly.
>>
>
>  From my POV it would be more interesting to do a comparison in action by
> implementing PROV Constraints (http://www.w3.org/TR/prov-constraints/) in
> all proposed solutions (ShEx, SPIN, Shapes, ICV, OWL).
> I think PROV is a nice use case because it has a moderate complexity and
> can reveal weaknesses / strengths in terms of expressivity, readability &
> compactness. A plus would be to capture the constraints of the PROV
> ontology in CWA.
> Paul Groth already made an attempt to port these constraints in SPIN [1]
> but I am not aware if these are complete or optimized.
>
>  In addition this would be a great contribution to the PROV community.
>
>  @Arthur, Eric, Jose
> It would be great if you could shed some light in the actual differences
> between ShEx and Shapes (besides the syntax and the property group
> extensions by ShEx)
>
>  Best,
> Dimitris
>
>  [1]
> https://github.com/pgroth/prov-constraints-validator-spin/blob/master/python/prov-constraints.py
>
>
>
>>
>> Peter, would this be an acceptable direction for you?
>>
>> Thanks,
>> Holger
>>
>>
>>
>> On 8/3/14, 9:14 AM, Peter F. Patel-Schneider wrote:
>>
>>> I have indicated that I am satisfied with the current mention of
>>> possible solutions at the end of Section 3.
>>>
>>> The work currently mentioned there is targeted towards RDF validation.
>>>  I am not in favour of including work that is not targeted towards RDF
>>> validation. If SPARQL fits into this category then I am not in favour of
>>> including SPARQL in this part of the charter at all.
>>>
>>> I have never indicated that all possible solutions have to be included
>>> in the charter.  Suggesting this is just inflammatory.  I have never
>>> indicated that no possible solutions can be included in the charter.
>>>  Suggesting this is also inflammatory.
>>>
>>> I am in favour of including multiple possible solutions, and in favour
>>> of including the ones that I think have sufficient gravitas.
>>>
>>>
>>>
>>> Why do you think that SPARQL should be given the prominent place in the
>>> charter that it has in your suggested wording for deliverables?
>>>
>>>
>>> peter
>>>
>>>
>>>
>>>
>>>
>>> On 08/02/2014 03:37 PM, Irene Polikoff wrote:
>>>
>>>> Sort of. I believe you are interpreting "a blank sheet" in a very
>>>> literal sense of the words which is clearly not what I meant. Other than
>>>> that, I wanted to clarify if you are saying:
>>>>
>>>> 1) It is OK to state the possible solution in the charter as long as it
>>>> is not mentioned in the deliverables section or
>>>> 2) It is OK to state the possible solution in the charter as long as it
>>>> is not SPARQL or
>>>> 3) The charter should not mention any possible solutions anywhere or
>>>> 4) The charter should equally mention all possible solutions that may
>>>> exist in the world irrespective of their maturity and the number of such
>>>> possible alternatives or
>>>> 5) some combination of the above or something else altogether
>>>>
>>>> Irene
>>>>
>>>> -----Original Message-----
>>>> From: Peter F. Patel-Schneider [mailto:pfpschneider@gmail.com]
>>>> Sent: Saturday, August 02, 2014 6:11 PM
>>>> To: Irene Polikoff; 'Arthur Ryman'; public-rdf-shapes@w3.org
>>>> Subject: Re: Proposed change to the charter, section 4. Deliverables,
>>>> Recommendation Track
>>>>
>>>> You indeed have misunderstood my position.
>>>>
>>>> I don't think that I have previously indicated that starting with a
>>>> blank sheet is suboptimal, although I do agree that it is generally not a
>>>> good idea.
>>>>    No charter draft that I have seen does start with a blank sheet, so
>>>> this is somewhat of a moot point.
>>>>
>>>> There are several implemented and deployed systems that claim to
>>>> provide constraints for RDF.  Not all of them are given meaning in terms of
>>>> SPARQL.
>>>> There is new work that claims to provide constraints for RDF. It is not
>>>> based on SPARQL at all.  I have seen no work showing that SPARQL is
>>>> adequate as an underpinning of all these systems.  Under these
>>>> circumstances I feel that it is completely wrong to have SPARQL mentioned
>>>> at all in the deliverables of the working group.
>>>>
>>>> It this clear enough for you?
>>>>
>>>> peter
>>>>
>>>>
>>>>
>>>>
>>>> On 08/02/2014 02:54 PM, Irene Polikoff wrote:
>>>>
>>>>> Peter,
>>>>>
>>>>> I thought you agreed that starting with a blank sheet has proven to be
>>>>> suboptimal to ensuring success of a working group and its timely progress.
>>>>> And that while you were not against SPARQL per se, you were concerned with
>>>>> mandating its use in case the working group finds that it does not satisfy
>>>>> requirements.
>>>>>
>>>>> Since my proposed wording addresses both of the issues, I must have
>>>>> misunderstood your position.
>>>>>
>>>>> Irene
>>>>>
>>>>> -----Original Message-----
>>>>> From: Peter F. Patel-Schneider [mailto:pfpschneider@gmail.com]
>>>>> Sent: Saturday, August 02, 2014 5:09 PM
>>>>> To: Irene Polikoff; 'Arthur Ryman'; public-rdf-shapes@w3.org
>>>>> Subject: Re: Proposed change to the charter, section 4. Deliverables,
>>>>> Recommendation Track
>>>>>
>>>>> Again, your proposed wording goes far beyond simply mentioning a
>>>>> possible solution.  Your proposed wording says that a particular approach
>>>>> is to be followed unless it is shown to be inadequate.
>>>>>
>>>>> I do not support this proposed wording.  I do support wording like
>>>>> what is currently at the end of Section 3.
>>>>>
>>>>> peter
>>>>>
>>>>>
>>>>> On 08/02/2014 01:21 PM, Irene Polikoff wrote:
>>>>>
>>>>>> Because it identifies a possible solution and says that if it proves
>>>>>> to be inadequate, the working group will choose another approach. Thus, the
>>>>>> prime candidate is identified, but the group is not mandated to use it.
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Peter F. Patel-Schneider [mailto:pfpschneider@gmail.com]
>>>>>> Sent: Saturday, August 02, 2014 4:18 PM
>>>>>> To: Irene Polikoff; 'Arthur Ryman'; public-rdf-shapes@w3.org
>>>>>> Subject: Re: Proposed change to the charter, section 4. Deliverables,
>>>>>> Recommendation Track
>>>>>>
>>>>>> Why would you think that this would be acceptable to me? This goes
>>>>>> well beyond pointing at possible solutions or mentioning possible starting
>>>>>> points.
>>>>>>
>>>>>> peter
>>>>>>
>>>>>> On 08/02/2014 01:13 PM, Irene Polikoff wrote:
>>>>>>
>>>>>>> Then, Arthur's strawman with the modification below should be
>>>>>>> acceptable:
>>>>>>>
>>>>>>> The WG MUST produce:
>>>>>>>
>>>>>>> 1. A high-level RDF vocabulary that expresses commonly occurring
>>>>>>> constraints.
>>>>>>> 2. The semantics of the high-level constraints expressed in terms of
>>>>>>> SPARQL or, if SPARQL proves to be unsuitable for the use cases determined
>>>>>>> by the group, in an alternative language.
>>>>>>> 3. An RDF extension mechanism for expressing additional constraints,
>>>>>>> expressed in SPARQL.
>>>>>>>
>>>>>>> The WG MAY produce:
>>>>>>>
>>>>>>> 1. A new compact, human readable syntax for expressing constraints
>>>>>>> with a corresponding semantics expressed in SPARQL or, if SPARQL proves to
>>>>>>> be unsuitable for the use cases determined by the group, in an alternative
>>>>>>> language.
>>>>>>> 2. A specification of how constraint validation interacts with
>>>>>>> inference.
>>>>>>> 3. A specification for graph normalization.
>>>>>>> [1] http://www.w3.org/2014/data-shapes/charter
>>>>>>>
>>>>>>> Irene
>>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: Peter F. Patel-Schneider [mailto:pfpschneider@gmail.com]
>>>>>>> Sent: Saturday, August 02, 2014 1:17 AM
>>>>>>> To: Irene Polikoff; 'Arthur Ryman'; public-rdf-shapes@w3.org
>>>>>>> Subject: Re: Proposed change to the charter, section 4.
>>>>>>> Deliverables, Recommendation Track
>>>>>>>
>>>>>>> I don't see much wrong in pointing at potential solutions, and even
>>>>>>> less mentioning possible starting points, but that's not what the proposed
>>>>>>> change to the charter is. Instead the proposed change mandates SPARQL as
>>>>>>> the semantics of constraints.  I think that this is in advance of any
>>>>>>> worked-out proposal for actually using SPARQL for this purpose.
>>>>>>>
>>>>>>> If it turns out that SPARQL can be used to specify the semantics of
>>>>>>> constraints, then it may be reasonable to use SPARQL for this purpose.
>>>>>>> However, mandating SPARQL's use even before its suitability has been
>>>>>>> demonstrated doesn't seem to me to be a good idea.
>>>>>>>
>>>>>>> peter
>>>>>>>
>>>>>>>
>>>>>>> On 08/01/2014 06:54 PM, Irene Polikoff wrote:
>>>>>>>
>>>>>>>> Not necessarily. As Jeremy Carroll said in one of the previous
>>>>>>>> e-mails "W3C experience indicates that a WG with a blank sheet at the
>>>>>>>> beginning often delivers the wrong stuff, late - and the broad ship that
>>>>>>>> sails ends up as a narrow clique on arrival".
>>>>>>>>
>>>>>>>> It is better to set a charter that identifies the prime candidate.
>>>>>>>> As the work proceeds, the group may decide that the candidate doesn’t meet
>>>>>>>> key requirements, but having initial stake in the ground is important to
>>>>>>>> the effectiveness of the group, its ability to deliver on time and quality
>>>>>>>> of its deliverables.
>>>>>>>>
>>>>>>>> Irene
>>>>>>>>
>>>>>>>> -----Original Message-----
>>>>>>>> From: Peter F. Patel-Schneider [mailto:pfpschneider@gmail.com]
>>>>>>>> Sent: Friday, August 01, 2014 5:53 PM
>>>>>>>> To: Arthur Ryman; public-rdf-shapes@w3.org
>>>>>>>> Subject: Re: Proposed change to the charter, section 4.
>>>>>>>> Deliverables, Recommendation Track
>>>>>>>>
>>>>>>>> All these arguments may be fine, but isn't that up to the working
>>>>>>>> group to decide?
>>>>>>>>
>>>>>>>> peter
>>>>>>>>
>>>>>>>>
>>>>>>>> On 08/01/2014 02:42 PM, Arthur Ryman wrote:
>>>>>>>>
>>>>>>>>> Peter,
>>>>>>>>>
>>>>>>>>> Thx for the response. I'm glad that we agree on making the
>>>>>>>>> compact, human-friendly syntax optional.
>>>>>>>>>
>>>>>>>>> Here is my rationale for advocating for the use of SPARQL.
>>>>>>>>>
>>>>>>>>> 1. We need to be precise about the meaning of constraints.
>>>>>>>>> Therefore, we need to select some formalism for expressing the
>>>>>>>>> semantics.
>>>>>>>>>
>>>>>>>>> 2. The candidates for expressing semantics include:
>>>>>>>>> 2.1 Natural language
>>>>>>>>> 2.2 OWL ICV
>>>>>>>>> 2.3 SPARQL
>>>>>>>>> 2.4 Z
>>>>>>>>> 2.5 some other existing formal language
>>>>>>>>> 2.6 a new specification language that the wg invents
>>>>>>>>>
>>>>>>>>> Pros and Cons
>>>>>>>>>
>>>>>>>>> 2.1 Natural language is imprecise and non-executable
>>>>>>>>> 2.2 OWL ICV is well-defined and executable, but not a W3C standard
>>>>>>>>> and is not expressive enough as a general constraint language
>>>>>>>>> 2.3 SPARQL is a W3C standard, is very expressive, and is
>>>>>>>>> executable
>>>>>>>>> 2.4 Z is very expressive but not well known and is non-executable
>>>>>>>>> 2.5 There are many other formal specification languages. Does
>>>>>>>>> anyone want to advocate for one?
>>>>>>>>> 2.6 A new formalism - not the core focus of the workgroup.
>>>>>>>>>
>>>>>>>>> 3. Some one will need to build a reference implementation. A
>>>>>>>>> SPARQL implementation will be easy to build if the semantics of
>>>>>>>>> the constraints are in SPARQL.
>>>>>>>>>
>>>>>>>>> 4. We want the specification to be implemented and adopted. SPARQL
>>>>>>>>> is a known quantity and many implementations exist.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> __________________________________________________________________
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _____
>>>>>>>>> Arthur Ryman, PhD
>>>>>>>>>
>>>>>>>>> Chief Data Officer, Rational
>>>>>>>>> Chief Architect, Portfolio & Strategy Management Distinguished
>>>>>>>>> Engineer | Master Inventor | Academy of Technology
>>>>>>>>>
>>>>>>>>> Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> From:   "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
>>>>>>>>> To:     Arthur Ryman/Toronto/IBM@IBMCA, public-rdf-shapes@w3.org,
>>>>>>>>> Date:   08/01/2014 05:22 PM
>>>>>>>>> Subject:        Re: Proposed change to the charter, section 4.
>>>>>>>>> Deliverables, Recommendation   Track
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I do agree that the emphasis in the charter on creating a
>>>>>>>>> human-readable syntax is misplaced and that this deliverable
>>>>>>>>> should be made optional. The proposal here, however, does very
>>>>>>>>> much more than fixing this problem, and I view most of the other
>>>>>>>>> changes in the proposal as undesirable.
>>>>>>>>>
>>>>>>>>> Why should the group be required to specify semantics in terms of
>>>>>>>>> SPARQL?
>>>>>>>>> There hasn't even been anything to show that SPARQL is adequate
>>>>>>>>> for this purpose.  Why should the group be required to specify two
>>>>>>>>> ways of expressing constraints, and one of them be SPARQL itself?
>>>>>>>>> There hasn't been anything to show that this division is needed.
>>>>>>>>> Why should a human-readable syntax for constraints be new?  There
>>>>>>>>> hasn't been anything to show that existing syntaxes are unsuitable
>>>>>>>>> for this purpose.  I don't think that it is appropriate to tie the
>>>>>>>>> hands of the working group in any of these ways.
>>>>>>>>>
>>>>>>>>> I do agree that the group should be required to define the meaning
>>>>>>>>> of constraints.  This was a peculiar lack in the deliverables.
>>>>>>>>>
>>>>>>>>> So my proposal would be to change the recommendation track
>>>>>>>>> deliverables to
>>>>>>>>>
>>>>>>>>> something like:
>>>>>>>>>
>>>>>>>>> 1. A syntax and semantics for shapes specifying how to construct
>>>>>>>>> shape expressions and how shape expressions are evaluated against
>>>>>>>>> RDF graphs.
>>>>>>>>>
>>>>>>>>> 2. An RDF vocabulary for expressing these shapes in RDF triples,
>>>>>>>>> so they can be stored, queried, analyzed, and manipulated with
>>>>>>>>> normal RDF tools.
>>>>>>>>>
>>>>>>>>> 3. OPTIONAL A specification of how shape verification interacts
>>>>>>>>> with inference.
>>>>>>>>>
>>>>>>>>> 4. OPTIONAL A compact, human-readable syntax for expressing shapes.
>>>>>>>>>
>>>>>>>>> I would prefer the third deliverable to be required, but I'm not
>>>>>>>>> going to complain if it is optional.
>>>>>>>>>
>>>>>>>>> Although there are three syntaxes mentioned in these deliverables,
>>>>>>>>> in keeping with the usual RDF situation there is nothing saying
>>>>>>>>> that all of these three need to be different or even that they are
>>>>>>>>> not all the same.  (Well, nothing beyond the implausibility of
>>>>>>>>> using RDF triples as the basis of a compact, human-readable
>>>>>>>>> syntax.)
>>>>>>>>>
>>>>>>>>> peter
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 08/01/2014 12:44 PM, Arthur Ryman wrote:
>>>>>>>>>
>>>>>>>>>> The output of the wg is defined by its deliverables. Here is the
>>>>>>>>>> current text [1]
>>>>>>>>>>
>>>>>>>>>> Recommendation Track:
>>>>>>>>>> 1.      Compact, human readable syntax for expressing constraints
>>>>>>>>>> on RDF
>>>>>>>>>> graph patterns (aka shapes), suitable for the use cases
>>>>>>>>>> determined by
>>>>>>>>>>
>>>>>>>>> the
>>>>>>>>>
>>>>>>>>>> group. This syntax might be a variation of an existing standard,
>>>>>>>>>> such as templates for SPARQL, or something new, such as ShExC.
>>>>>>>>>> 2.      An RDF vocabulary, such as Resource Shapes 2.0, for
>>>>>>>>>> expressing
>>>>>>>>>> these shapes in RDF triples, so they can be stored, queried,
>>>>>>>>>> analyzed,
>>>>>>>>>>
>>>>>>>>> and
>>>>>>>>>
>>>>>>>>>> manipulated with normal RDF tools.
>>>>>>>>>> The WG MAY produce a Recommendation for graph normalization.
>>>>>>>>>>
>>>>>>>>>> This text is not acceptable to IBM because of the primary
>>>>>>>>>> emphasis it places on defining a possibly new compact, human
>>>>>>>>>> readable syntax.
>>>>>>>>>> I believe this concern has been expressed repeatedly by many
>>>>>>>>>> people on the mailing list. Many people have indicated a strong
>>>>>>>>>> preference for
>>>>>>>>>>
>>>>>>>>> building
>>>>>>>>>
>>>>>>>>>> on existing standards. However, we have not seen any
>>>>>>>>>> corresponding modification of the charter. I'd therefore like to
>>>>>>>>>> propose a strawman change to this section of the charter and
>>>>>>>>>> invite comment.
>>>>>>>>>> Here is the proposed new text:
>>>>>>>>>> The WG MUST produce:
>>>>>>>>>> 1. A high-level RDF vocabulary that expresses commonly occurring
>>>>>>>>>> constraints.
>>>>>>>>>> 2. The semantics of the high-level constraints expressed in terms
>>>>>>>>>> of SPARQL.
>>>>>>>>>> 3. An RDF extension mechanism for expressing additional
>>>>>>>>>> constraints, expressed in SPARQL.
>>>>>>>>>> The WG MAY produce:
>>>>>>>>>> 1. A new compact, human readable syntax for expressing
>>>>>>>>>> constraints with
>>>>>>>>>>
>>>>>>>>> a
>>>>>>>>>
>>>>>>>>>> corresponding semantics expressed in SPARQL.
>>>>>>>>>> 2. A specification for graph normalization.
>>>>>>>>>> [1] http://www.w3.org/2014/data-shapes/charter
>>>>>>>>>>
>>>>>>>>>> Regards,
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> __________________________________________________________________
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _
>>>>>>>>> _____
>>>>>>>>>
>>>>>>>>>> Arthur Ryman, PhD
>>>>>>>>>>
>>>>>>>>>> Chief Data Officer, Rational
>>>>>>>>>> Chief Architect, Portfolio & Strategy Management Distinguished
>>>>>>>>>> Engineer | Master Inventor | Academy of Technology
>>>>>>>>>>
>>>>>>>>>> Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>>
>
>
>  --
>  Dimitris Kontokostas
> Department of Computer Science, University of Leipzig
> Research Group: http://aksw.org
> Homepage:http://aksw.org/DimitrisKontokostas
>
>
>


-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org
Homepage:http://aksw.org/DimitrisKontokostas