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Re: Inverse properties, was: Re: Socialnetworks of a person or organization

From: <martin.hepp@ebusiness-unibw.org>
Date: Mon, 14 Apr 2014 20:18:41 +0200
Cc: Gregg Kellogg <gregg@greggkellogg.net>, Dan Brickley <danbri@google.com>, Charles McCathie Nevile <chaals@yandex-team.ru>, W3C Web Schemas Task Force <public-vocabs@w3.org>, Guha Guha <guha@google.com>
Message-Id: <2632A9E8-B60C-4B26-8E49-B4BCA2AB2D5F@ebusiness-unibw.org>
To: Stéphane Corlosquet <scorlosquet@gmail.com>
Hi Stéphane:

On 14 Apr 2014, at 20:05, Stéphane Corlosquet <scorlosquet@gmail.com> wrote:

> This was my initial reaction too. Microdata was designed to be a simpler alternative to RDFa, but we're talking about making it closer to RDFa and in doing so, we're defeating its purpose of being simple. There is also the argument that this kind of reverse property feature (like additionalType) are available in other formats. We keep bending microdata/schema.org to support features it was originally designed for, features which are available in JSON-LD and RDFa.

I think the main difference between Microdata and RDFa is that the underlying philosphy of Microdata is to add meta-data to an HTML DOM while the philosophy of RDFa was to find a way to weave in an RDF graph into an HTML document. But that is just a very personal view.

And I would argue that adding a mechanism for reverse properties makes Microdata simpler for several cases and not more complicated.

> We should also consider a prefix-based convention like itemprop="rev-author" or itemprop="rev-alumni". It eliminates the need to maintain a custom list of reverse properties and make the processing trivial since properties are CamelCase, and it's easy to strip the prefix and reverse the relation.
> 

I am not sure whether you mean that that should be done 

1. at the level of schema.org,
2. as a social convention or for all Microdata vocabularies, or
3. in the Microdata spec.

If it is #3, I described that option in
    https://www.w3.org/wiki/WebSchemas/InverseProperties#A_prefix_mechanism

But I think this is not a very beautiful approach, since we are overloading the property string with something else.

Also, at least in theorey we would then have to update the Microdata spec, too, and exclude property names that start with "rev-".

Of course, we could solve the issue solely at the level of schema.org (#1) and mechanically define reverse properties for all properties using your mechanism. But then we have the confusion of additionalProperty at the level of 100+ properties - that there are inverse properties that are just needed in Microdata. And you expand the size of the vocabulary, which is what I wanted to prevent with my initial post.

Martin


> Steph.
>  
> 
> Gregg
> 
> > So I still think that updating the Microdata spec is the preferred way to go.
> >
> > Martin
> >
> >
> >
> > On 14 Apr 2014, at 18:50, Gregg Kellogg <gregg@greggkellogg.net> wrote:
> >
> >> I've been thinking about updates to the Microdata to RDF note [1] as well. In particular, abandoning the registry [2], which rapidly becomes outdated, and making use of the JSON-LD context, which one day soon (?) will show up at http://schema.org. One opportunity this might give us is to use @reverse term definitions in the JSON-LD context as the value of an @itemprop. If schema.org defined and supported such term definitions, this would provide a mechanism to get the effect of reverse properties without needing to change Microdata.
> >>
> >> This works well for Microdata when interpreted as RDF, but is more problematic in the original transformation to Microdata JSON, where the data model is that of a tree, and not a graph. I'm sure it could be done, but it does provide some challenges to the processing algorithm, whereas doing this in the context of an RDF transformation is more natural.
> >>
> >> The example from the Wiki, a schema.org context could assert the following term:
> >>
> >> {
> >> "@context": {
> >>   "@vocab": "http://schema.org/",
> >>   "isCreatorOf": {"@reverse": "creator"},
> >>   ...
> >> }
> >> }
> >>
> >> You could then use this in microdata as follows:
> >>
> >> <div id="creator" itemprop="creator" itemscope itemtype="http://schema.org/Person">
> >>      <span itemprop="name">William Shakespeare</name>
> >>      <link itemProp="isCreatorOf" href="http://www.freebase.com/m/0yq9mqd">
> >> </div>
> >>
> >> In a way, this is like defining reverse properties, except that it does not confuse the vocabulary, but really just exists as a syntactic shortcut.
> >>
> >> This would also be useful to describe @itemprop values as being in a list or not, which may be useful for properties such as event, itemListElement and recipeInstructions, if the schema.org JSON-LD context made use of the @container: @list term definition.
> >>
> >> While we're at it, we could re-visit the need for md:item in the RDF transformation to keep all top-level @itemscope entries in order. This was a relic from the original RDF transformation in Microdata that in retrospect, I think provides little value in an RDF interpretation.
> >>
> >> IMO, the Microdata JSON model is not as useful as the RDF model for use with schema.org, so focusing on improving the transformation of Microdata to RDF makes more sense, and more closely aligns it with JSON-LD and RDFa.
> >>
> >> Gregg Kellogg
> >> gregg@greggkellogg.net
> >>
> >> [1] http://www.w3.org/TR/microdata-rdf/
> >> [2] http://www.w3.org/ns/md
> >>
> >> On Apr 14, 2014, at 7:57 AM, martin.hepp@ebusiness-unibw.org wrote:
> >>
> >>> I just added eight markup examples of how useful a new keyword for reverse properties in Microdata would be:
> >>>
> >>>  https://www.w3.org/wiki/WebSchemas/InverseProperties#Examples_and_Use_Cases
> >>>
> >>> Best
> >>> Martin
> >>>
> >>> -----------------------------------
> >>> martin hepp  http://www.heppnetz.de
> >>> mhepp@computer.org          @mfhepp
> >>>
> >>>
> >>
> >>
> >
> 
> 
> 
> 
> 
> -- 
> Steph.
Received on Monday, 14 April 2014 18:19:11 UTC

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