W3C home > Mailing lists > Public > public-vocabs@w3.org > June 2012

Re: additionalType property, vs extending Microdata syntax for multiple types

From: Martin Hepp <martin.hepp@ebusiness-unibw.org>
Date: Mon, 18 Jun 2012 15:53:19 +0200
Cc: Peter Mika <pmika@yahoo-inc.com>, Dan Brickley <danbri@danbri.org>, Ivan Herman <ivan@w3.org>, "public-vocabs@w3.org" <public-vocabs@w3.org>, Ramanathan Guha <guha@google.com>, Jeni Tennison <jeni@jenitennison.com>
Message-Id: <9B5025E3-2A23-45D5-B4FA-CB916E961874@ebusiness-unibw.org>
To: Egor Antonov <elderos@yandex-team.ru>
Hi Egor:

>> A minor concern is that the name additionalType implies that somehow one 
>> type is more important than the other.
It is, because the main type defines the context for the properties, while additionalType points to an identifier that gives information about type membership from an external vocabulary.

RDFa does not need this distinction, since it does not follow a frame-based modeling pattern.

Also note that any Microdata pattern is always "a hack" in the sense that parsers have to be updated manually in order to be in sync with the evolution with the vocabulary, because there is AFAIK no standard way of encoding the Microdata processing rules.


On Jun 18, 2012, at 12:11 PM, Egor Antonov wrote:

> Agreed with Peter. "additionalType" is not a part of the (ontology) schema, but a hack for microdata.
> We cannot save compatibility with microdata anyway, because all the parsers need to be rewritten to understand schema.org.
> If so, why do we handle it as ontology schema addition and not as new markup standard?
> Let's just make a microdata extension for schema.org.
> PS
> It will be strange to have "additionalType" property while "mainType" doesn't exist.
> --
> Egor
> 16.06.2012, 19:28, "Peter Mika" <pmika@yahoo-inc.com>:
>> Let me add my $0.02...
>> My main concern is that schema.org is and should be about the schema, 
>> not the syntax. The reason of adding this property is to patch 
>> microdata, but if schema.org defines this term, it will be available for 
>> all syntaxes (microdata, RDFa, possibly soon OData). In both microdata 
>> and RDFa, we would end up with two ways of defining types (using 
>> typeof/itemtype vs. additionalType). Standard parsers however will only 
>> see one type (the one expressed using the standard mechanism).
>> A minor concern is that the name additionalType implies that somehow one 
>> type is more important than the other.
>> Cheers,
>> Peter
>> On 6/16/12 7:48 AM, Dan Brickley wrote:
>>  On 16 June 2012 06:55, Ivan Herman<ivan@w3.org>  wrote:
>>  On Jun 15, 2012, at 20:26 , Dan Brickley wrote:
>>  HTML5 Microdata, as defined in
>>  http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#encoding-microdata
>>  ... has only limited support for describing multiple types that
>>  something belongs to. In particular it requires they are described
>>  using a single schema.
>>  For Good Relations integration (and other scenarios) people have asked
>>  for a way of listing more types within schema.org markup.
>>  * One model is to use RDFa 1.1 (Lite), where this is quite natural.
>>  * Another is to add (as a workaround) a new property, e.g. called
>>  'type' or 'additionalType', to schema.org's vocab (Martin requests
>>  this in http://www.w3.org/wiki/WebSchemas/GoodRelations )
>>  * A 3rd is to stretch
>>  http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#items
>>  to allow different namespaces to be used.
>>  I think that the third option is not obvious. The issue is that, in microdata, two notions, namely the typing of an item and the vocabulary used in that item, are conflated. The vocabulary information (hence the interpretation of the terms in the item) is deduced from the itemtype value(s). Hence the restriction in the current spec to restrict multiple types to be in the same vocabulary. Technically, it would be possible to declare that the order in the attribute's value counts, ie, the first type value determines the vocabulary, but that would be terribly error-prone and I hence do not believe it would be a good idea.
>>  It would require a more substantial change in the microdata spec (essentially introducing the equivalent of RDFa's @vocab) to solve that properly. I do not see that happening.
>>  Yes. I think it is well appreciated that RDFa 1.1 handles this better.
>>    I don't think anyone expects Microdata to change a lot more, and I
>>  don't see anyone with the energy/interest to keep pushing for these
>>  kinds of changes/improvements in Microdata. As you say, it wouldn't be
>>  easy. The "main type comes first" design was all I could think of,
>>  too.
>>  Which leaves us with the first or the second option. I am obviously biased here, but I think the first option is clearly better in this respect...
>>  The question is then, what do we say for all those publishers who are
>>  on board the Microdata train? A lot of people have worked hard to get
>>  colleagues/stakeholds (and tools!) adopting Microdata, over the last
>>  year. While RDFa is a good thing, we want to be careful to support
>>  early adopters too, and have sensible advice for them (other than
>>  're-do everything with a new syntax'). Which is what makes
>>  'additionalType' attractive. But the concern there is ... if we go
>>  that route, validators/checkers will need to understand the attribute
>>  since it is almost an extension of the underlying syntax...
>>  cheers,
>>  Dan
> -- 
> Egor Antonov
> http://staff.yandex-team.ru/elderos

martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen

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Received on Monday, 18 June 2012 13:53:57 UTC

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