On 12 Jun 2011, at 14:40, Danny Ayers wrote: > [snip] > Aside from containing a different bunch of bits because of the > encoding, sasha-photo.jpg could be a lossy-compressed version of > sasha-photo.gif, containing less pixel information yet sharing many > characteristics. > > All ok so far..? > > If so, from this we can determine that a representation of a resource > need not be "complete" in terms of the information it contains to > fulfill the RDF statement and the HTTP contract.
A photo and a graph work in essentially the same way. They both set restrictions on possible worlds of which they are true. A photo restricts the number of possible worlds to those that are visually equivalent to the picture taken. A graph is true of all the possible worlds where those relations holds - which is usually infinitely large. In either case the meaning of a graph or document is a set of possible worlds. A set is an object - one can speak of it - but a very different kind of object from what you may think of as what appears in the picture. As such there is indeed a fundamental logical difference between a document and objects in the world. And that also explains why a photo is not clearly about one thing or another - though of course given that it is a restriction on the way things can be, it limits the things the document could be about. As stated in a previous mail, the same photo can be about the eiffel tower, a sunset, a beautiful view of Paris, a vacation experience, a friend that appears in the picture, a murder that was commited at that moment,... The photo remains the same in all those descriptions, and it can be tagged in all those ways, which is why it is good to have names for each of those things that are different from the photo. Each of those should have definite descriptions to help identify the referents from the description. Henry Social Web Architect http://bblfish.net/
