]> 2012-05-27T21:37:12-04:00 Joshua Shinavier Networked Graphs Joshua Taylor 1 In '''6. IMPLEMENTATION''', the authors describe their algorithm for determining the fixedpoint of a graph/view. They write, "In some more details, the procedure starts with the true statements, which are extensionally lister, or which can be derived from views, which do not use negation. //Though, I thought that views ''could'' use negation…// We call this underestimate ''U''₁. Statements in ''U''₁ are known to be true. ''U''₁ is used to compute an overestimate ''O''₁ by evaluating all views against this set of true statements. '''The result will be an overestimate, because ''U''₁ was still incomplete and therefore bound negation will succeed in too many cases.''' //So views ''can'' contain negation…//" (emphasis added) I do not see how they can guarantee that ''O''₁ will be an overestimate. It is generated based on ''U''₁ whose elements are known to be true, but which is not yet the set of all true statements. Then if ''O''₁ does not depend on views using negation, it would seem that ''O''₁ could be another underestimate. In '''5.1 Requirements …, RDF Schema''' the authors state "that NGs are expressive enough to alternatively model the RDFS inference rules as view definitions." I imagine a a ''U''₁ containing "X rdf:type A", "A rdf:subClassOf B", and "B rdf:subClassOf C", which would lead to an ''O''₁ containing ''U''₁ as a subset, and also "X rdf:type B", and perhaps "X rdf:type C". Yet ''O''₁ is clearly not an overestimate. What am I missing here? Joshua Shinavier Networked Graphs Question for the Presentation Joshua A. Taylor Question asked by Question asked Presentation Questions