Hi Markus,

On 01.06.2016 12:58, Markus Kroetzsch wrote:
On 01.06.2016 10:46, Sebastian Hellmann wrote:
https://en.wikipedia.org/wiki/Unique_name_assumption

The UNA is a principle in formal logic and knowledge representation. It is not really related to this discussion. For example, standard DBMS all make the UNA, but you can still have many identifiers (keys) for the same object in a database.

Then the database does not use UNA. The above sentence reads like you could have two primary keys, but then still have them pointing to the same row. UNA means, if you have two identifiers A, B you add a triple A owl:differentFrom B at all times.

Sebastian

The explanation is that UNA refers to the internal interpretation of symbols in the database, whereas the outside, user-level notions of "identifier" and "concept" may be represented in a database by many symbols and their relationships.

Markus


On 01.06.2016 10:02, Markus Kroetzsch wrote:
Re "a concept cannot have multiple IDs":

There seems to be some major misconception underlying the below email.
It is certainly not the case that identifiers must be unique by
definition. Every identifier must identify a unique object, but a single
object can have multiple identifiers. This is standard meaning of
"identifier" applies to URIs just as well as to IDs in databases and all
kinds of other areas.

Requiring that every concept can only be identified in one way would
make things very hard in decentralised data ecosystems such as LOD. In
fact, it would already cause problems in individual databases, which
often need to merge identifiers as they improve over time (e.g.,
MusicBrainz Ids 2ca98ac1-62f0-4cdc-89ad-9d4b7602440a and
6a10f49d-e7db-40d3-a348-bbd5717ebbbe refer to the same concept).

Cheers,

Markus

On 31.05.2016 17:53,jacc...@petrobras.com.br  wrote:
Clarifying:

The function of an ID (identifier) is to identity a concept, not to
describe it. So they must be unique by definition, a concept can not
have multiple IDs . Multiple concepts may be equivalent to one another,
but that doesn't mean they are the same. If you have two different IDs
(i.e. the Unicode comparison of the strings results in mismatch) you
have by definition two different concepts. That is not what you want.
You want multiple labels for the same concept/ID.

The description of a concept (or definition, philosophically speaking)
is the whole group of other properties you ascribe to the concept by
referencing its ID, including as may human readable labels as you need
and relations to other concepts.  You can choose to use an automatic
generated ID in order to guarantee uniqueness or use manually ascribed
human readable strings, but with the later you must guarantee the
uniqueness by process (as is the case with DBpedia IDs, which are
derived from Wikipedia IDs).

It is not a RDF requirement for the IRIs to be simple (although that
saves parsing time) or human readable, but they MUST be unique and
stable, otherwise the identity of the concept is compromised.  Human
readable IDs are only helpful in manual edition of files, which happens only in examples and didactic purposes. Real world IDs are mostly UUIDs
   (universally unique IDs) generated by the system (for Java, see
java.util.UUID ). Some systems use prefixed URLs in order to embed
provenance into the ID, but that is a very, very bad practice:
provenance is metadata as any other, you should use specific properties
for that. IDs were not designed to provide any other semantics besides
identity.

Cheers.
=============================================
Marcelo Jaccoud Amaral
PETROBRAS
Tecnologia da Informação e Comunicações - Arquitetura Tecnológica
   (TIC/ARQTIC/AT)
=============================================
dum loquimur, fugetir invida aetas: carpe diem, quam minimum credula
postero.
-- Horatius





De: Katie Frey<kf...@cfa.harvard.edu>
Para: Markus Kroetzsch<markus.kroetz...@tu-dresden.de>
Cc: "DBpedia Discussion \(ML\)"<dbpedia-discussion@lists.sourceforge.net>
Data: 2016-05-31 11:50
Assunto: Re: [Dbpedia-discussion] Concept Identifiers
------------------------------------------------------------------------



Dear Markus,

Thank you for the insight. We might also try to assign both numeric and
descriptive IDs to a concept.  It seems as though best practices don't
really exist in this area, other than the general imperative to keep the
URIs simple and as stable as possible.

Best,
Katie
<https://www.wikidata.org/entity/Q544>

--
Katie E. Frey
John G. Wolbach Library, Harvard-Smithsonian Center for Astrophysics
60 Garden Street, MS-56, Cambridge, MA 02138
email: _kfrey@cfa.harvard.edu_<mailto:kf...@cfa.harvard.edu>| phone:
617-496-7579_
__http://astrothesaurus.org_ <http://astrothesaurus.org/>           |
_http://library.cfa.harvard.edu/_

"Surprising what you can dig out of books if you read long enough, isn’t
it?"
- Rand al'Thor (in Robert Jordan's The Shadow Rising, Book Four of the
Wheel of Time)

"This is insanity!"   "No, this is scholarship!"
- Yalb and Shallan (in Brandon Sanderson's Words of Radiance, Book Two
of the Stormlight Archive)

On Thu, May 26, 2016 at 4:06 PM, Markus Kroetzsch
<_markus.kroetzsch@tu-dresden.de_
<mailto:markus.kroetz...@tu-dresden.de>> wrote:
Dear Katie,

DBpedia mostly uses descriptive URIs that are based on the titles of
Wikipedia articles in a specific language. These URIs change if pages
are renamed, but for many concepts, this does not occur so often. You
would probably only notice it if you are using the URIs for several years.

If you instead want to use numeric IDs based on Wikipedia pages (or
DBpedia URIs), you can take them from Wikidata. These IDs are stable,
but not descriptive. They are kept unique in that they can only be
deleted but not reused. For example,
_http://dbpedia.org/page/Solar_System_is  currently the same as_
__https://www.wikidata.org/entity/Q544_.

The Wikidata URI uses content negotiation to redirect you to the HTML
page if you open it in a browser, and to RDF if you open it with an RDF
crawler. See _https://www.wikidata.org/wiki/Wikidata:Data_access_for
direct links to the RDF content.

To manually find out what the Wikidata ID is for a Wikipedia page, you
can go to the Wikipedia page and use the link to "Wikidata item" on the
left. To do this in an automated fashion, you can use the SPARQL
endpoint, e.g., with the query

SELECT *
WHERE {
<_https://en.wikipedia.org/wiki/Solar%20System_> schema:about ?item .
}

(try it in the Wikidata SPARQL UI: _http://tinyurl.com/jlk4fz2_)

The Wikidata Web API can also map page titles to IDs for you prefer JSON
over SPARQL:
_
__https://www.wikidata.org/w/api.php?action=wbgetentities&format=json&sites=enwiki&titles=Solar+System&props=_

Each of these methods can also be used to fetch many IDs at once. So
basically it is fairly straightforward to translate from DBpedia URIs to
Wikidata URIs. The mapping between the two changes over time only when
DBPedia URIs change their meaning (e.g., if "Solar System" is renamed to
"Solar System (astronomy)" or something).

Best regards,

Markus



On _26.05.2016 20_ <tel:26.05.2016%2020>:43, Katie Frey wrote:
Hello,

How are concept IDs handled for DBpedia? It looks like the concept URIs
are descriptive (i.e. for the concept_
__http://dbpedia.org/page/Solar_System_, the concept ID is
"Solar_System"). Are the descriptive IDs used throughout all of dbpedia
(back and front end) or are terms ultimately kept unique by using
numeric identifiers?

I've been developing a controlled vocabulary and I would also like to
use URIs so that my terms can be used with other linked data schemes.
My group and I have had a lot of discussions regarding the concept IDs;
some want them to be descriptive, based on the preferred term for each
concept so that they are human readable but this could cause problems if
the terms used to describe each concept change over time, others want
them to be randomly generated so that if the description of a term
drifts over time the URI for the concept will always remain static.

We are trying to figure out if there are any standards or best practices
we should be looking towards when it comes to concept IDs. Any
thoughts/comments/justifications would be appreciated.

Best,
Katie

--
Katie E. Frey
John G. Wolbach Library, Harvard-Smithsonian Center for Astrophysics
60 Garden Street, MS-56, Cambridge, MA 02138
email: _kfrey@cfa.harvard.edu_
<mailto:kf...@cfa.harvard.edu><mailto:_kfrey@cfa.harvard.edu_
<mailto:kf...@cfa.harvard.edu>>  |   phone:_
__617-496-7579_ <tel:617-496-7579> <tel:_617-496-7579_ <tel:617-496-7579>>_
__http://astrothesaurus.org_ <http://astrothesaurus.org/>          |
_http://library.cfa.harvard.edu/_

"Surprising what you can dig out of books if you read long enough, isn’t
it?"
- Rand al'Thor (in Robert Jordan's The Shadow Rising, Book Four of the
Wheel of Time)

"This is insanity!"   "No, this is scholarship!"
- Yalb and Shallan (in Brandon Sanderson's Words of Radiance, Book Two
of the Stormlight Archive)


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--
Markus Kroetzsch
Faculty of Computer Science
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__+49 351 463 38486_ <tel:%2B49%20351%20463%2038486>_
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All the best,
Sebastian Hellmann

AKSW/KILT research group at Leipzig University
Insitute for Applied Informatics (InfAI) at Leipzig University
DBpedia Association
Events:
* *April 24, 2016* Submission Deadline, SEMANTiCS 2016: Workshop &
Tutorial Proposals
<https://docs.google.com/document/d/1VOWyU9Oo2KOuRh09R9CJeC9aWcSNokDW4yHeuGHICPI/pub>
* *May 10th, 2016* Submission Deadline, SEMANTiCS 2016: Research &
Innovation Papers
<https://docs.google.com/document/d/1bYXVeO-vWwIctJgDv4rS3H5oFv0Yz_tyTo0xQcAEtPU/pub>
* *Sep 12th-15th, 2016* SEMANTiCS 2016, Leipzig <http://semantics.cc/>
Venha para a Alemanha como PhD: http://bis.informatik.uni-leipzig.de/csf
Projects: http://dbpedia.org, http://nlp2rdf.org,
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<http://www.w3.org/community/ld4lt>
Homepage: http://aksw.org/SebastianHellmann
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Thesis:
http://tinyurl.com/sh-thesis-summary
http://tinyurl.com/sh-thesis


--
All the best,
Sebastian Hellmann

AKSW/KILT research group at Leipzig University
Insitute for Applied Informatics (InfAI) at Leipzig University
DBpedia Association
Events:
* *April 24, 2016* Submission Deadline, SEMANTiCS 2016: Workshop & Tutorial Proposals <https://docs.google.com/document/d/1VOWyU9Oo2KOuRh09R9CJeC9aWcSNokDW4yHeuGHICPI/pub> * *May 10th, 2016* Submission Deadline, SEMANTiCS 2016: Research & Innovation Papers <https://docs.google.com/document/d/1bYXVeO-vWwIctJgDv4rS3H5oFv0Yz_tyTo0xQcAEtPU/pub>
* *Sep 12th-15th, 2016* SEMANTiCS 2016, Leipzig <http://semantics.cc/>
Venha para a Alemanha como PhD: http://bis.informatik.uni-leipzig.de/csf
Projects: http://dbpedia.org, http://nlp2rdf.org, http://linguistics.okfn.org, https://www.w3.org/community/ld4lt <http://www.w3.org/community/ld4lt>
Homepage: http://aksw.org/SebastianHellmann
Research Group: http://aksw.org
Thesis:
http://tinyurl.com/sh-thesis-summary
http://tinyurl.com/sh-thesis
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