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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:

   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.




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 UTC

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