Hi:

Why did you use exact match (P2888) instead of equivalent class (P1709) and equivalent property (P1628)?

peter

On 9/22/18 5:07 AM, Andra Waagmeester wrote:

Hi Maarten,

We are actively mapping to other ontologies using the exact match P2888 property. The disease ontology is one example which is actively synchronized in Wikidata using the exact match property (P2888). This property is inspired by the SKOS:exact match property. SKOS it self had more mapping properties and I think it is a good idea to introduce some of the other SKOS mapping properties in Wikidata such broad match and narrow match.

Andra

On Sat, Sep 22, 2018 at 7:30 AM Maarten Dammers <maarten@mdammers.nl mailto:maarten@mdammers.nl> wrote:

Hi everyone,

Last week I presented Wikidata at the Semantics conference in Vienna (
https://2018.semantics.cc/ ). One question I asked people was: What is
keeping you from using Wikidata? One of the common responses is that
it's quite hard to combine Wikidata with the rest of the semantic web.
We have our own private ontology that's a bit on an island. Most of our
triples are in our own private format and not available in a more
generic, more widely use ontology.

Let's pick an example: Claude Lussan. No clue who he is, but my bot
seems to have added some links and the item isn't too big. Our URI is
http://www.wikidata.org/entity/Q2977729 and this is equivalent of
http://viaf.org/viaf/29578396 and
http://data.bibliotheken.nl/id/thes/p173983111 . If you look at
http://www.wikidata.org/entity/Q2977729.rdf this equivalence is
represented as:
<wdtn:P214 rdf:resource="http://viaf.org/viaf/29578396"/>
<wdtn:P1006 rdf:resource="http://data.bibliotheken.nl/id/thes/p173983111"/>

Also outputting it in a more generic way would probably make using it
easier than it is right now. Last discussion about this was at
https://www.wikidata.org/wiki/Property_talk:P1921 , but no response
since June.

That's one way of linking up, but another way is using equivalent
property ( https://www.wikidata.org/wiki/Property:P1628 ) and equivalent
class ( https://www.wikidata.org/wiki/Property:P1709 ). See for example
sex or gender ( https://www.wikidata.org/wiki/Property:P21) how it's
mapped to other ontologies. This won't produce easier RDF, but some
smart downstream users have figured out some SPARQL queries. So linking
up our properties and classes to other ontologies will make using our
data easier. This is a first step. Maybe it will be used in the future
to generate more RDF, maybe not and we'll just document the SPARQL
approach properly.

The equivalent property and equivalent class are used, but not that
much. Did anyone already try a structured approach with reporting? I'm
considering parsing popular ontology descriptions and producing reports
of what is linked to what so it's easy to make missing links, but I
don't want to do double work here.

What ontologies are important because these are used a lot? Some of the
ones I came across:
* https://www.w3.org/2009/08/skos-reference/skos.html
* http://xmlns.com/foaf/spec/
* http://schema.org/
* https://creativecommons.org/ns
* http://dbpedia.org/ontology/
* http://vocab.org/open/
Any suggestions?

Maarten


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Interesting. I am very interested in this topic. Is there a page on Wikidata where all this information is collected? One day I read about the disease ontology mentioned by Andra Waagmeester. But I don't know where I can track the progress of the mapping, not only to the disease ontology.

Thanks in advance.

Regards, Iván

On 9/22/18 1:13 PM, Federico Leva (Nemo) wrote:

Maarten Dammers, 22/09/2018 14:28:

...

What ontologies are important because these are used a lot? Some of the ones I came across:

• https://www.w3.org/2009/08/skos-reference/skos.html
• http://xmlns.com/foaf/spec/
• http://schema.org/

Since 2016 there was some progress: https://github.com/schemaorg/schemaorg/issues/280 https://github.com/schemaorg/schemaorg/issues/1186

The last time I looked into it was for music: https://www.wikidata.org/?oldid=297764900#schema.org/MusicRecording

Mapping properties is tedious but a relatively amount of work (tens of hours rather than hundreds) can make a significant difference.

Federico

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@Andra Waagmester: I am a little disconcerted by the property P288 "exact match" https://www.wikidata.org/wiki/Property:P2888. I see it is mostly used to link entities, not properties, and I can't figure out how it differs from an external id (unless it's just a convenient way of linking concepts to databases that do not have an external id in Wikidata?)

On Sat, 22 Sep 2018 at 15:55, Peter F. Patel-Schneider < pfpschneider@gmail.com> wrote:

It is indeed helpful to link the Wikidata ontologies to other ontologies, particularly ones like the DBpedia ontology and the schema.org ontology. There are already quite a few links from the Wikidata ontology to several other ontologies, using the Wikidata equivalent class and property properties. Going through and ensuring that every class and property, for example, in the DBpedia ontology or the schema.org ontology is the target of a correct (!) link would be useful. Then, as you indicate, it is not so hard to query Wikidata using the external ontology or map Wikidata information into information in the other ontology.

The Wikidata ontology is much larger (almost two million classes) and much more fine grained than most (or maybe even all) other general-purpose ontologies. This is appealing as one can be much more precise in Wikidata than in other ontologies. It does make Wikidata harder to use (correctly) because to represent an entity in Wikidata one has to select among many more alternatives.

This selection is harder than it should be. The Wikidata ontology is not well organized. The Wikidata ontology has errors in it. There is not yet a good tool for visualizing or exploring the ontology (although there are some useful tools such as https://tools.wmflabs.org/bambots/WikidataClasses.php and http://tools.wmflabs.org/wikidata-todo/tree.html).

So it is not trivial to set up good mappings from the Wikidata ontology to other ontologies. When setting up equivalences one has to be careful to select the Wikidata class or property that is actually equivalent to the external class or property as opposed to a Wikidata class or property that just happens to have a similar or the same label. One also has to be similarly careful when setting up other relationships between the Wikidata ontology and other ontologies. As well, one has to be careful to select good relationships that have well-defined meanings. (Some SKOS relationships are particuarly suspect.) I suggest using only strict generalization and specialization relationships.

So I think that an effort to completely and correctly map several external general-purpose ontologies into the Wikidata ontology would be something for the Wikidata community to support. Pick a few good external ontologies and put the needed effort into adding any missing mappings and checking the mappings that already exist. Get someone or some group to commit to keeping the mapping up to date. Announce the results and show how they are useful.

Peter F. Patel-Schneider Nuance Communications

On 9/22/18 4:28 AM, Maarten Dammers wrote:

...

Hi everyone,

Last week I presented Wikidata at the Semantics conference in Vienna ( https://2018.semantics.cc/ ). One question I asked people was: What is

keeping

...

you from using Wikidata? One of the common responses is that it's quite

hard

...

to combine Wikidata with the rest of the semantic web. We have our own

private

...

ontology that's a bit on an island. Most of our triples are in our own

private

...

format and not available in a more generic, more widely use ontology.

Let's pick an example: Claude Lussan. No clue who he is, but my bot

seems to

...

have added some links and the item isn't too big. Our URI is http://www.wikidata.org/entity/Q2977729 and this is equivalent of http://viaf.org/viaf/29578396 and http://data.bibliotheken.nl/id/thes/p173983111 . If you look at http://www.wikidata.org/entity/Q2977729.rdf this equivalence is

represented as:

...

<wdtn:P214 rdf:resource="http://viaf.org/viaf/29578396%22/%3E <wdtn:P1006 rdf:resource="http://data.bibliotheken.nl/id/thes/p173983111

"/>

...

Also outputting it in a more generic way would probably make using it

easier

...

than it is right now. Last discussion about this was at https://www.wikidata.org/wiki/Property_talk:P1921 , but no response

since June.

...

That's one way of linking up, but another way is using equivalent

property (

...

https://www.wikidata.org/wiki/Property:P1628 ) and equivalent class ( https://www.wikidata.org/wiki/Property:P1709 ). See for example sex or

gender

...

( https://www.wikidata.org/wiki/Property:P21) how it's mapped to other ontologies. This won't produce easier RDF, but some smart downstream

users

...

have figured out some SPARQL queries. So linking up our properties and

classes

...

to other ontologies will make using our data easier. This is a first

step.

...

Maybe it will be used in the future to generate more RDF, maybe not and

we'll

...

just document the SPARQL approach properly.

The equivalent property and equivalent class are used, but not that

much. Did

...

anyone already try a structured approach with reporting? I'm considering parsing popular ontology descriptions and producing reports of what is

linked

...

to what so it's easy to make missing links, but I don't want to do

double work

...

here.

What ontologies are important because these are used a lot? Some of the

ones I

...

came across:

• https://www.w3.org/2009/08/skos-reference/skos.html
• http://xmlns.com/foaf/spec/
• http://schema.org/
• https://creativecommons.org/ns
• http://dbpedia.org/ontology/
• http://vocab.org/open/

Any suggestions?

Maarten

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It is indeed used to link entities and not necessarily only those that don't have an external id. External IDs can be problematic if you want to use them in federated SPARQL queries. In theory you would able to compile the IRI from the external ID and the underlying resulver URL, however there are two problems here.. The resolver URL in wikidata allows only one variable (i.e. $1) and various ontologies require additional processing to compile a URI. the simple example being the identifier that in its literal form used the pattern PREFIX:Identifier, whereas a URI it has PREFIX_identifier. This can mostly be resolved using the BIND operator in the SPARQL query, but since this is an expensive operation, more complex federated queries can time out. Also having to parse an external lID, to get its URI feels a bit patchy. Having a property that directly captures a single mapping to an external namespace can thus be quite helpful.

When I explored a mapping property from Wikidata to external IRI namespaces (including ontologies) there were basically three external mapping properties, being OWL;sameAs, schema:sameAs and Skos.exactMatch. OWL sameas dictated that both items should interchangeable, which is not the case. schema:Sameas and SKOS.exact match were the alternatives. Since SKOS comes with more mapping relations [1], I proposed the property exact match a few years back. Since its acceptance, we have been successfully using it running federated queries to and from Wikidata. Initially, I intended to propose the other mapping relationships from SKOS as similarity properties in Wikidata, since I didn't run into the proper use case yet, but it is still on my radar.

The property P2888 has been quite functional since, if I may say.

[1] https://www.w3.org/TR/skos-reference/#mapping

On Sat, Sep 22, 2018 at 10:09 AM Ettore RIZZA ettorerizza@gmail.com wrote:

@Andra Waagmester: I am a little disconcerted by the property P288 "exact match" https://www.wikidata.org/wiki/Property:P2888. I see it is mostly used to link entities, not properties, and I can't figure out how it differs from an external id (unless it's just a convenient way of linking concepts to databases that do not have an external id in Wikidata?)

On Sat, 22 Sep 2018 at 15:55, Peter F. Patel-Schneider < pfpschneider@gmail.com> wrote:

...

It is indeed helpful to link the Wikidata ontologies to other ontologies, particularly ones like the DBpedia ontology and the schema.org ontology. There are already quite a few links from the Wikidata ontology to several other ontologies, using the Wikidata equivalent class and property properties. Going through and ensuring that every class and property, for example, in the DBpedia ontology or the schema.org ontology is the target of a correct (!) link would be useful. Then, as you indicate, it is not so hard to query Wikidata using the external ontology or map Wikidata information into information in the other ontology.

The Wikidata ontology is much larger (almost two million classes) and much more fine grained than most (or maybe even all) other general-purpose ontologies. This is appealing as one can be much more precise in Wikidata than in other ontologies. It does make Wikidata harder to use (correctly) because to represent an entity in Wikidata one has to select among many more alternatives.

This selection is harder than it should be. The Wikidata ontology is not well organized. The Wikidata ontology has errors in it. There is not yet a good tool for visualizing or exploring the ontology (although there are some useful tools such as https://tools.wmflabs.org/bambots/WikidataClasses.php and http://tools.wmflabs.org/wikidata-todo/tree.html).

So it is not trivial to set up good mappings from the Wikidata ontology to other ontologies. When setting up equivalences one has to be careful to select the Wikidata class or property that is actually equivalent to the external class or property as opposed to a Wikidata class or property that just happens to have a similar or the same label. One also has to be similarly careful when setting up other relationships between the Wikidata ontology and other ontologies. As well, one has to be careful to select good relationships that have well-defined meanings. (Some SKOS relationships are particuarly suspect.) I suggest using only strict generalization and specialization relationships.

So I think that an effort to completely and correctly map several external general-purpose ontologies into the Wikidata ontology would be something for the Wikidata community to support. Pick a few good external ontologies and put the needed effort into adding any missing mappings and checking the mappings that already exist. Get someone or some group to commit to keeping the mapping up to date. Announce the results and show how they are useful.

Peter F. Patel-Schneider Nuance Communications

On 9/22/18 4:28 AM, Maarten Dammers wrote:

...

Hi everyone,

Last week I presented Wikidata at the Semantics conference in Vienna ( https://2018.semantics.cc/ ). One question I asked people was: What is

keeping

...

you from using Wikidata? One of the common responses is that it's quite

hard

...

to combine Wikidata with the rest of the semantic web. We have our own

private

...

ontology that's a bit on an island. Most of our triples are in our own

private

...

format and not available in a more generic, more widely use ontology.

Let's pick an example: Claude Lussan. No clue who he is, but my bot

seems to

...

have added some links and the item isn't too big. Our URI is http://www.wikidata.org/entity/Q2977729 and this is equivalent of http://viaf.org/viaf/29578396 and http://data.bibliotheken.nl/id/thes/p173983111 . If you look at http://www.wikidata.org/entity/Q2977729.rdf this equivalence is

represented as:

...

<wdtn:P214 rdf:resource="http://viaf.org/viaf/29578396%22/%3E <wdtn:P1006 rdf:resource="

http://data.bibliotheken.nl/id/thes/p173983111%22/%3E

...

Also outputting it in a more generic way would probably make using it

easier

...

than it is right now. Last discussion about this was at https://www.wikidata.org/wiki/Property_talk:P1921 , but no response

since June.

...

That's one way of linking up, but another way is using equivalent

property (

...

https://www.wikidata.org/wiki/Property:P1628 ) and equivalent class ( https://www.wikidata.org/wiki/Property:P1709 ). See for example sex or

gender

...

( https://www.wikidata.org/wiki/Property:P21) how it's mapped to other ontologies. This won't produce easier RDF, but some smart downstream

users

...

have figured out some SPARQL queries. So linking up our properties and

classes

...

to other ontologies will make using our data easier. This is a first

step.

...

Maybe it will be used in the future to generate more RDF, maybe not and

we'll

...

just document the SPARQL approach properly.

The equivalent property and equivalent class are used, but not that

much. Did

...

anyone already try a structured approach with reporting? I'm considering parsing popular ontology descriptions and producing reports of what is

linked

...

to what so it's easy to make missing links, but I don't want to do

double work

...

here.

What ontologies are important because these are used a lot? Some of the

ones I

...

came across:

• https://www.w3.org/2009/08/skos-reference/skos.html
• http://xmlns.com/foaf/spec/
• http://schema.org/
• https://creativecommons.org/ns
• http://dbpedia.org/ontology/
• http://vocab.org/open/

Any suggestions?

Maarten

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I think probably a distinction can be made in terms of whether your use case involves exporting items into other ontologies, versus importing items from other ontologies into wikidata. You'll have different issues with granularity in either direction and they may not be entirely symmetrical, so you might actually have to model it in both directions, difficulties of querying aside.

My use case involves creating wikidata items from citoid https://www.mediawiki.org/wiki/Citoid items, so I have been thinking of modelling the Zotero/Citation Style Language on wikidata as part of using citoid on Wikidata (which uses the Zotero ontology.) Unlike schema.org there's no canonical url pointing to different properties, so I'd actually like to create an item for each Zotero / Citoid property and actually store the entire schema itself on wikidata. (This has the additional use case being able to provide documentation of the properties using reasonator as well!)

I've created an example on test wikidata here: https://test.wikidata.org/wiki/Q173241. Here we have the property publicationTitle, which in citoid/Zotero, has a string value. In wikidata we would want this to point to an item corresponding to the publication so we'd use "published in" property as equivalent. There's also hierarchy modelled here, with websiteTitle being a subclass of publicationTitle: https://test.wikidata.org/wiki/Q173239

This is a different way of modelling it versus adding an equivalent property to the wikidata property a la https://www.wikidata.org/wiki/Property:P356. For my use case, this would be the easiest model for querying the properties. But I share Stas's concern here that this could quickly explode the number of items. How many items called "title" do we need, because "title" is a property in a lot of examples?

You can see in my example I made my property and instance of both a citoid property and a zotero property. They mostly overlap, but there are few citoid properties which are not Zotero properties. CSL properties are even trickier. I think if they have the same exact name string and all other properties and equivalencies they can be put in one item but I don't anticipate that happening much with other less similar ontologies.

Not exactly sure what to use for the name of the property to store the string, i.e. "publicationTitle" either - might have to create a new property for that (I checked, Official Name doesn't take "JSON" as a valid language!)

(The other thing is I've now gone down the rabbit hole of thinking about modelly markup and programming languages. In a JSON object there's a limited number of types (Object, string, array, integer etc), and I've had a go of adding that on test wikidata - but it kind of opens up the idea of actually adding in a full model of a programming language which sounds crazy until you consider that we've done basically that with the addition of lexographical data!)

Cheers, Marielle

On Sun, Sep 23, 2018 at 8:57 PM Stas Malyshev smalyshev@wikimedia.org wrote:

Hi!

...

That's one way of linking up, but another way is using equivalent property ( https://www.wikidata.org/wiki/Property:P1628 ) and equivalent class ( https://www.wikidata.org/wiki/Property:P1709 ). See for example

It is technically possible to add values for P1628 into RDF export. However, the following questions arise:

1. Are we ready to claim these are exact equivalents? Sometimes semantic

meanings differ, and some properties have class requirements - e.g. http://schema.org/illustrator expects value to be of class Person, but of course Wikidata item would not have that class. Same for the subject

• it expected to be of a class Book, but won't be. This may confuse some

systems. Is that ok?

2. How we deal with multiple ontologies with the same meanings? E.g.

https://www.wikidata.org/wiki/Property:P21 has 4 equivalent properties. There might be more. Do we want to generate them all? Why there are two properties for the same FOAF ontology - is that right?

3. If you change P1628, that does not automatically make all items with

the relevant predicate update. You need to do an extensive update process - which is currently does not exist, and for popular property may require significant resources to complete, some properties have millions of uses.

Using P1709 is even more tricky since Wikidata ontology (provided we call what we have an ontology, which may also not be acceptable to some) is rather different from traditional semantic ontologies, and we do not really enforce any of the rules with regard to classes, property domain/ranges, etc. and have frequent and numerous exceptions to those.

-- Stas Malyshev smalyshev@wikimedia.org

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