Hu2007discovering question 1 by lebo

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CSCI 6966 Advanced Semantic Web (Fall 2008)

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• Lesson 1, Lesson 2, Lesson 3, Lesson 4, Lesson 5, Lesson 6,
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A Question from Tim Lebo about Joshua Taylor presents Discovering Simple Mappings Between Relational Database Schemas and Ontologies:

In Definition 3, a mapping m is a 5-tuple <id,u,v,t,f>, where u is an element of the relational schema, v is an element of the ontology, t is a relationship (e.g., equivalence or subsumption), and f is a confidence measure. Phase II of the matching process views each element of the relational schema and ontology as a "virtual document" that is compared to the other elements' "virtual documents" using the the TF/IDF cosine measure. In a mapping m, id, u, v, and f are providing in this process.

1. How is t (equivalence/subsumption) determined for a given mapping?
2. Does the use the subsequent third Phase, Validity Mapping Consistency, indicate a lack of confidence in the previous stage's ability to match? What else "doesn't make sense" in the matching that hasn't been filtered out?

Question answered by: Joshua Taylor Answer:

1. The authors specify that a mapping m contains a relationship t that holds between the u and v. I think this definition is confusing as the authors never make use of this t. Simple mappings seem to find equivalence relationships, and contextual mappings seem to find subsumption relationships. Personally, I think that it would be useful if the system allowed human users re-run certain phases, and to make adjustments between runs. Phase 3 checks the consistency of attribute/property mappings, and this could be facilitated if users could step in and clarify the relation/class mappings (to specify equivalence, subsumption, &c.).
2. As I mentioned in the preceding item, the consistency checking phase checks the consistency of mappings between, assuming (or provided) that the relation/class mappings have been computed correctly. I think the unspoken assumption is that relation/class mappings are more likely to be correct (and this is probably reasonable, particularly if the Des function has access to good descriptions, and if the number of entity relations in the database and classes in the ontology is small). So, I don't think that the presence of Phase 3 indicates a lack of confidence so much as a recognition that attribute/property matching is more difficult than relation/class matching, but is easier in the presence of the latter.