Key differences between Properties and Items:

* Properties have a data type, items don't.
* Items have sitelinks, Properties don't.
* Items have Statements, Properties will support Claims (without sources).

The software needs these constraints/guarantees to be able to take shortcuts,
provide specialized UI and API functionality, etc.

Yes, it would be possible to use items as properties instead of having a
separate entity type. But they are structurally and functionally different, so
it makes sense to have a strict separate. This makes a lot of things easier, 

* setting different permissions for properties
* mapping to rdf vocabularies

More fundamentally, they are semantically different: an item describes a concept
in "the real world", while a property is a structural component used for such a

Yes, properies are simmilar to data items, and in some cases, there may be an
item representing the same concept that is represented by a property entity. I
don't see why that is a problem, while I can see a lot of confusion arising from
mixing them.

-- daniel

Am 28.05.2014 09:25, schrieb David Cuenca:
> Since the very beginning I have kept myself busy with properties, thinking 
> about
> which ones fit, which ones are missing to better describe reality, how 
> integrate
> into the ones that we have. The thing is that the more I work with them, the
> less difference I see with normal items.... and if soon there will be 
> statements
> allowed in property pages, the difference will blur even more.
> I can understand that from the software development point of view it might 
> make
> sense to have a clear difference. Or for the community to get a deeper
> understanding of the underlying concepts represented by words.
> But semantically I see no difference between:
> cement (Q45190) <emissivity (P1295)> 0.54
> and
> cement (Q45190) <emissivity (Q899670)> 0.54
> Am I missing something here? Are properties really needed or are we adding
> unnecessary artificial constraints?
> Cheers,
> Micru
> _______________________________________________
> Wikidata-l mailing list

Daniel Kinzler
Senior Software Developer

Wikimedia Deutschland
Gesellschaft zur Förderung Freien Wissens e.V.

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