Shangguan MetaQuery Presentation

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Presentation given at CSCI 6966 Advanced Semantic Web (Fall 2008) - Lesson 8

• Speaker: Zhenning Shangguan
• Title: Querying for Meta Knowledge
• Authors: Bernhard Schueler, Sergej Sizov, Steffen Staab, Duc Thanh Tran
• Conference: WWW2008
• URL: http://www2008.org/papers/pdf/p625-schueler.pdf
• Date of Presentation: 2008/10/16

Questions

ID	Question	Name	Answer
Querying Meta Knowledge Ankesh	In section 4.3.1 authors mention about distributive and collective reading as they choose the former, i.e. the certainty attached with G1 in RDF is considered to be certainty attached with each RDF statement in G1 and the certainty of all facts (n in number) in G1 considered together is certainty*certainty*....n-times. Have I understood it correctly? If not please do not read further! Could we considered certainty attached with G1 in terms of fuzzy logic rather than in probabilistic sense? Further, adopting the same distributive reading we could argue that the certainty of all facts in G1 considered together is minimum of certainty of all the facts, instead of their products? There is a possibility that certain meta-property values are available for G1 and not for G2. Have authors discussed this possibility while querying named graphs G1 and G2? If I have missed something, again don't read further! Specifically consider Example 5.9. What happens if Iftime(x1) is known but Iftime(x2) is not known and we are considering Iftime(x1 intersection x2). Comment: Idea of replicating meta statements on graphs to individual RDF statements doesn't appear neat! Lots of redundancy, unnecessary load on storage space.	Ankesh Khandelwal
Schueler2008querying question 1 by lebo	When describing their design choices, the authors state, "For compliance with existing applications that access the repository in a common way (e.g. using SPARQL queries), we do not modify existing user data." The preservation of user data is clearly a important. But they disregard RDF reification as an option, saying "This requirement does not allow us to use mechanisms like RDF reification, which decompose existing triples and fully change the representation model." In what way would RDF reification (the use of rdf:Statement) decompose and fully change the representation model?	Tim Lebo
Shangguan MetaQuery Presentation Gregory Todd Williams 1	The paper suggests that the implemented extension of metadata querying is compatible with the SPARQL spec. However, it's unclear how any results from an extended query could be returned within the confines of the existing spec. Footnote 3 mentions that returning query results and meta knowledge in two different graphs requires "some implementation-specific mechanism." As a potential solution to this issue, why would the query results in example 5.15 not be better expressed using standard RDF reification? Similarly, section 4.3.2 describes serializing RDF+ to RDF, but relies on a named-graphs serialization not part of the standard RDF model. Does this conflict with the claim of compatibility?	Gregory Todd Williams
Shangguan MetaQuery Presentation Gregory Todd Williams 2	Example 5.12 shows query results including meta knowledge about each variable mapping. For example, the mapping { ?x = <JamesHendler> } is associated with { certainty=0.9, time=5/5/07}. The paper gives examples of meta knowledge property operators for both certainty and time. However, all the examples used produce simple scalar values for these meta knowledge properties. Would operators that produce complex data types work with this system? If so, how might such data be serialized in query results? For example, if instead of being interested in the most recent timestamp of data used in a variable mapping (Itime(x1 ^ x2) = max(Itime(x1),I(x2))), what if we wanted a timestamp range of all data used to construct the variable mapping (something like Itime(x1 ^ x2) = { min(Itime(x1),I(x2)), max(Itime(x1),I(x2)) })? This would seem to complicate the modeling of meta knowledge as single triples.	Gregory Todd Williams
Shangguan MetaQuery Presentation Jesse Weaver	As Greg pointed out, values of metaknowledge are simply scalar values. I notice that one of the examples is a confidence value. This opens a whole new can of worms. Often, a confidence value itself needs metaknowledge or reification to indicate how it was derived. Otherwise, it is somewhat arbitrary. Does this approach allow metaknowledge of metaknowledge?	Jesse Weaver
Shangguan MetaQuery Presentation Joshua Taylor 1	One of the design choices made by the authors is that their system employs Syntax extensions. While many authors and designers seem to follow the approach of extending systems rather than building extensions within a system, syntactical extensions present the problem that the users of the services must be aware of said extensions (whether this means end users, or programmers working with the system). In this case, there are extensions to the SPARQL query language. Do you think that the benefits of this system could be realized in a way that doesn't require syntactic extensions?	Joshua A. Taylor

Attendees

Tim Lebo