Some initial ideas on the statement. I realize that this is not priority in the first phase, but perhaps on the wiki a place could be created to collect some thoughts like those below?
http://meta.wikimedia.org/wiki/Wikidata/Notes/Data_model#The_Metamodel explains:
Statement = (StatementID, Property, Value, Qualifier*, Reference*) The StatementID is a unique identifier for the given statement and used only internally and for export. A Property is defined on a property page. This definition includes a type. The structure of the Value is given by the type of the property. Simple types could demand an EntityID or a number. More complex types could demand dates, date ranges, numbers with units, a geocoordinate, a geo shape, etc.
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1. Will Property include information on observation/recording/measurement methodology?
2. What happens if the main entity has variants or parts for which values are recorded?
An example is car models, where typically the revisions sold under the same name are subsumed in one Wikipedia article. Example:
http://en.wikipedia.org/wiki/Renault_Kangoo with different length / weight in the "subclass" info boxes for first/second generation.
Cars also easily serve as an example for variable parts, see in http://en.wikipedia.org/wiki/%C5%A0koda_Roomster the list of engine specifications. The engines are not Wikipedia entities in their own right.
3. Values may be well defined RDF-resources, but now available in Wikipedia.
In my work, many statements I would like to express in a future Wikidata are not allowed as Wikipedia articles at all. You can express "Wowereit" is_mayor_of "Berlin, Germany" but not "Plantago lanceolata" has_leaf_shape "lanceolate" because http://en.wikipedia.org/wiki/Lanceolate is a redirect to http://en.wikipedia.org/wiki/Leaf_shape
I personally would love to have illustrated definitions of things people want to learn about being allowed on Wikipedia, but the argument is generally that Wikipedia is not Wiktionary.
I believe Wikidata should right from the start be defined to allow references to Wiktionary as well as Wikipedia. And while we are at it, references to Commons as well (semantic image annotation...)
This would change Wikipedialink = (Title, LanguageId, Badge?) to Link = (Project, LanguageId, Title, Badge?)
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Gregor