Rob Gonzalez of Cambridge Semantics recently commented on a LinkedIn thread started by Michael Uschold. Uschold asked the question, "How is semantic technology more flexible than relational technology?" One commenter stated, "If you 'mess up' your choice of initial vocabulary, then semantic systems have similar sorts of problems to relational systems, in that you may have to restructure the vocabulary at a later date (just like you have to restructure relational schemas), and hence restructure the data. My experience suggests that such restructuring happens (far?) less often with semantic systems than with relational systems, and that the restructuring is easier, since you can always treat your data as one big list of triples."
Gonzalez replied, "I actually take a different view. I believe that messing up ontologies is unavoidable. A simple example is two people publishing similar data sets at different times without reusing each other's ontologies. This happens all the time. The power that RDF, OWL, and SPARQL give you in this circumstance is to quickly build maps between related constructs in a way that is not possible in the relational world (you'd be in ETL hell). In some cases, a simple owl:sameAs gets you there. In others, a basic SPARQL CONSTRUCT expression and you're golden. Either way, the translation layer is cheap."
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