Protagoras and foaf:Person

πάντων χρημάτων μέτρον έστιν άνθρωπος,
των μεν όντων ως έστιν,
των δε ουκ όντων ως ουκ εστίν

About 2,500 years later, does the famous Protagoras aphorism still apply to things (χρήματα) in the Linked Data universe? The usual translation "Man is the measure of all things" could be misleading when put in parallel with the RDF motto "Everything is a Thing". The ancient Greek χρήμα has actually a more restrictive and pragmatic meaning, namely those things that one actually either holds and uses or badly needs, hence goods, possessions, money. And with this meaning in mind, the Protagoras aphorism is much less mysterious. Man(kind) is or should be the measure of what is needed and useful to mankind, either what one holds (things which are) or what one lacks (things which are not).

In the Linked Data universe, if everything is a thing, not everything is used or even useful.

Is your linked data vocabulary 5-star?

You have created and published on the Web linked data following the best practices and you think they are now 5-star data. But are the vocabularies, RDFS or OWL classes and properties your dataset is using, also 5-star? At the above link one can read some kind of wishful thinking expressed by Tim Berners-Lee:

The third rule, that one should serve information on the web against a URI, is, in 2006, well followed for most ontologies … One can, in general, look up the properties and classes one finds in data, and get information from the RDF, RDFS, and OWL ontologies including the relationships between the terms in the ontology. 

Unfortunately, even in 2012, this is yet far from being true in general.