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Re: Cardinality of schema.org properties

From: Martin Hepp <martin.hepp@ebusiness-unibw.org>
Date: Thu, 20 Oct 2011 10:43:51 +0200
Cc: public-vocabs@w3.org
Message-Id: <3A39C377-4DCA-48A2-9F99-3E0017DF76C8@ebusiness-unibw.org>
To: Philip Jägenstedt <philipj@opera.com>
Hi all:

In GoodRelations, we always indicate the cardinality information as part of the label of the property. This has several advantages:

1. It is available in multiple syntaxes and formalisms, so it does not break if you use GoodRelations in any other Entity-Attribute-Value environment (e.g. outside of RDF).

2. You can still easily generate data quality rules by parsing the string with regex, since the format is always the same:

e.g. 
   has currency (1..1)

3. It is intuitive for people from RDBMS / conceptual modeling communities.

Furthermore, since it is not possible to stop people breaking cardinality constraints on a Web scale, you cannot enforce consistency rules as in a closed-world RDBMS anyway, so the question is not how to prevent this, but how to

1. communicate the recommended cardinalities and
2. how to handle violations at a data consumer side.

Note that language information makes the cardinality problem a bit trickier than assumed at first glance, because you have cases where you want to say that e.g. each product has just one description per language.

See

    http://www.heppnetz.de/ontologies/goodrelations/v1.html#conventions

Martin

On Oct 20, 2011, at 10:19 AM, Philip Jägenstedt wrote:

> On Thu, 20 Oct 2011 01:22:02 +0200, John Panzer <jpanzer@google.com> wrote:
> 
>> I'm trying to determine how to know what the intended cardinality of any
>> given schema.org defined property.
> 
> I asked about this and got this answer: [1]
> 
> On Thu, Jun 16, 2011 at 06:56, Guha <guha@google.com> wrote:
> 
>> Right now, it is always allowed to have multiple values.
>> In the future, we could/should introduce a property of properties that
>> specifies when a property may have only a single value.
> 
> Not exactly a satisfactory situation, but there it is.
> 
> [1] http://groups.google.com/group/schemaorg-discussion/browse_thread/thread/95dfc4aa1ab89dbf?pli=1
> 
> -- 
> Philip Jägenstedt
> Core Developer
> Opera Software
> 
Received on Thursday, 20 October 2011 08:44:23 GMT

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