- From: Andy Seaborne <andy.seaborne@talis.com>
- Date: Wed, 21 Jul 2010 16:05:00 +0100
- To: Sandro Hawke <sandro@w3.org>
- CC: SPARQL Working Group <public-rdf-dawg@w3.org>
On 20/07/2010 7:22 PM, Sandro Hawke wrote: > Meanwhile, I've been meaning to send a question about our use of the > term "Graph", which is connected here. > > It seems to me there are two different common meanings for the term > "RDF Graph". To use the AI terms for each of them: > > 1. A Knowledge Base (KB); a specific repository or store of RDF > triples. As in, "Please update your graph to remove the triple > <a> <b> <c>." > > 2. A Formula; a mathematical set of RDF triples. As in, "Graph > G1 entails infinite other graphs". > > The most crisp distinction may be around identity. Two formulas are > identical if and only if they contain the same triples. Meanwhile, KBs > can have the same triples while remaining distinct. It also makes > sense to talk about the state of a KB, and a KB changing over time. It > makes no sense to say such things about a formula; it's just a pure > mathematical set. > > I think we can agree that formally, technically, only definition 2 > (formulas) is correct. But I think meaning two is in common use; I > expect most of us use it often. When I say "graph" in the sense of > definition 1, I mean it as shorthand for "graph storage location", > "graph data structure", or "graph store". In spoken language, the > context usually makes it clear whether people mean KB or formula. I think it's helpful to go back tot he work already done: The term "RDF graph" is defined in RDF Concepts: http://www.w3.org/TR/rdf-concepts/#section-rdf-graph RDF does not talk about mutability but on the web things can change - the (web) resource is changing from one (def 2) graph to another. I think I know what you are describing by formula, but the term is used in as somethign specific and maybe has different aspects. http://www.w3.org/TeamSubmission/n3/#Quoting [[ Formulae An RDF document parses to a set of statements, or graph. However RDF itelf has no datatype allowing a graph as a literal value. N3 extends RDF allows a graph itself to be referred to within the language, where it is known as a formula. ]] As well as allowing variables, it also is the value of a graph, not just a set of triples. Earlier writing on N3 explicit describes it as a literal. When comprised of ground terms, it behaves like a literal with datatype (the datatype needs to imply the syntax so there is a mapping from lexcial form to value space). Equality seems to be defined as bNode-isomorphic - or possibly RDF equivalent (which would involved leaning as well). Andy
Received on Wednesday, 21 July 2010 15:05:29 UTC