Theoharis2008graph presented by Tim Lebo 4 dec 2008

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Presentation given at CSCI 6966 Advanced Semantic Web (Fall 2008)#Lesson 13

slides

• Speaker: Tim Lebo
• Title: On Graph Features of Semantic Web Schemas
• Authors: Yannis Theoharis, Yannis Tzitzikas, Dimitris Kotzinos, Vassilis Christophides
• Conference: IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING
• URL: http://ieeexplore.ieee.org/iel5/69/4476622/04407710.pdf?tp=&arnumber=4407710&isnumber=4476622
• Date of Presentation: 2008/12/4

Questions

ID	Question	Name	Answer
Graph Features SWS	Authors quote numbers from a reference to show that the number of OWL ontologies is 6 times lesser than RDFS ontologies. I bet there are very few OWL ontologies that use cardinality restrictions. Inspite of these statistics I am tempted to ask- wouldn't it be relevant to discuss cardinality restrictions in the context of the work in this paper. Cardinality restrictions (special case- functional properties) on a property, relate a class (RESTRICTION) to the range of the property. In addition they restrict the out-degree (total-degree) which is very relevant here. Do you think the same, and if possible how do you think cardinality restrictions can be accounted for? This probably should have come before the previous question, but since first question led me to think of this one, i keep it second. Many properties are intended to take multiple values. For example a property that relates team to its members, say hasMember. If authors would have considered instance data this would have been accounted for. Therefore it may not be enough to consider a single edge <team, hasMember, players> for total-degree estimations. Do you also see that as a problem? How do you think we can resolve this issue, if there is one? This question is also in context of those minority ontologies in OWL. I could understand that in the case of allValuesFrom, say C = AllValuesFrom(P,A), we can have an edge <C, P, A>. However, it's not clear from the paper that how the authors take into account someValuesFrom feature of OWL. What about property hierarchy? It's an RDFS feature. My personal feeling is that its inclusion shouldn't affect the VR and CCDF values for total-degrees (do you think so?). Still.. do you think property hierarchies should have been discussed (or considered) by the authors?	Ankesh Khandelwal	You make a very valid point that just being an "OWL" ontology does not mean that you actually use all of the constructs (is typing classes to owl:Class sufficient for being "OWL"?). I would like to find out the answer to your bet, but I wouldn't place any myself. Why do you think that cardinality restrictions are not used? (TBD...) two three four
Theoharis2008graph GTW 1	Section 4C(3), Distribution of Class Levels, states that a class c has level 0 if it is the root, and p+0 where p is the level of its parent otherwise. However, it goes on to say "if c has more than one parents, then p is the maximum of their levels" and also "The biggest number of classes is observed between the middle and the maximum leaf level." Isn't this latter observation strongly suggested by the former stated preference of the maximum level of multi-parented classes? Does this choice affect the results? Is any indication given of the frequency of multi-parented classes in the analyzed schemas?	Gregory Todd Williams
Theoharis2008graph Joshua Taylor 1	When the authors analyze class hierarchies, they observe, to some extent, power law behavior. They point out that if class hierarchies were complete and balanced trees, then the power law behavior would be expected, and, on a related note, their analysis shows how actual class hierarchies differ from complete and balanced trees. Now, it might not be feasible (or possible) to perform such an experiment, but what might happen if some instance data were available, and the same analysis were performed on the class hierarchy with the exclusion of class which are not the most specific class of any (known) instance?	Joshua A. Taylor
Theoharis2008graph Joshua Taylor 2	The analysis on the class hierarchy is, presumably, based on rdfs:subClassOf, as well as some OWL properties. (On page 1 they list owl:unionOf and owl:intersectionOf, but it's not clear whether these are the only two they consider.) One goal of the authors' is to automatically generate realistic schemata. If they generate a class hierarchy using just RDFS vocabulary, they will necessarily be generating a consistent ontology. If they use only RDFS, owl:unionOf, and owl:intersectionOf, they will generate a consistent ontology (I think). However, if they start to analyze and include, e.g., owl:disjointWith, they can begin to generate inconsistent ontologies. 1) Are they already performing analysis with the features of OWL that could express inconsistencies? 2) How might they avoid generating inconsistent ontologies (aside from simply checking the consistency of an ontology once it's been generated)?	Joshua A. Taylor
Theoharis2008graph presented by Tim Lebo 4 dec 2008 Jesse Weaver	Throughout the paper, it is mentioned that the findings of the paper can be used to create more realistic, synthetic datasets. Out of curiousity, has any research been done to see if existing synthetic datasets (e.g., LUBM) conform to the findings of this paper? This would help give some indication of how much the application of these findings will improve the generation of synthetic datasets.	Jesse Weaver

theoharis2008graph

http://dx.doi.org/10.1109/TKDE.2007.190735