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Yes, if the ontology marks the property as inverse with "owl:inverseOf", it can be followed backwards.

It is a good behavior to avoid inverse properties.

See

Tim Berners-Lee http://dig.csail.mit.edu/breadcrumbs/node/72

http://richard.cyganiak.de/blog/2006/06/an-rdf-design-pattern-inverse-property-labels/

It is close to impossible to make years into URIs, because years are part of calendars (gregorian is just one calendar type), where time events are defined as time instants or periods. You always have a numeric unit in it. As a result, you would have millions and millions of different URIs, a situation which is not possible to handle efficiently in an implementation, and very cumbersome for users.

Search engines are smarter. If they are required to search for all 16th century dramatists or plays written in Elizabethan England, they do not operate on RDF graphs but on inverted files where filters can be defined. No need to worry for that on RDF level.

Best,

Jörg


On Mon, Apr 20, 2015 at 8:54 PM, Kelley McGrath <[log in to unmask]> wrote:

This would seem to be a basic question, but I was asked the other day and I wasn't sure how to answer. Looking at a linked data graph that says that Hamlet - has creator - Shakespeare, there is an arrow pointing from Hamlet to Shakespeare. This person said they assumed that you can go the other way, too. Obviously Hamlet has creator Shakespeare logically implies that Shakespeare created Hamlet. However, the RDF statement has directionality so from a practical point of view, what happens when someone starts from Shakespeare rather than Hamlet? Is there some way for them to traverse the statement backwards or does the opposite statement need to be explicitly made (which would seem to create a nightmare for data maintenance)?

How about if the endpoint is a literal, say Shakespeare has birth year 1564? This would not seem to work backwards so maybe we should be making years into URIs so we can find all the 16th century dramatists or plays written in Elizabethan England.

Kelley