August 2009
Intermediate to advanced
456 pages
14h 8m
English
Content preview from Foundations of Semantic Web Technologies
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276 Foundations of Semantic Web Technologies
7.1.6.5 Errors
Most filter functions can only be meaningfully applied to certain kinds of
input data. The function +, e.g., can be used to compute the sum of two
numbers, but it does not have a natural d efin ition for the case where URIs
are given as inputs. Unf ortunately, it is not possible to prevent such situations
by careful query construction: even if a particular RDF property is intended to
have only numerical literals as values, it is always possible that a given RDF
database includes triples where this is not the case. RDF is not powerful
enough to enforce the use of intended datatypes. Moreover, variables that are
used in an optional graph pattern may happen to be unbound, which is again
not a suitable ...
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