| Abstract |
The Semantic Web (SW) is an evolving extension of the World Wide
Web in which Web content can be expressed not only in natural
language, but also in a format that can be read and used by software
agents, thus permitting them to find, share and integrate
information more easily. In order to cope with the evolving nature
of the Semantic Web we need effective and efficient support for
building advanced SW synchronization and versioning services. RDF
Deltas, reporting the differences that exist between two RDF knowledge bases (KBs)
have been proven to be crucial in order to reduce the amount of data
that need to be exchanged and managed over the network in order to
synchronize distributed Data Bases and to reduce the storage space
needed for managing different versions of RDF KBs.
This Thesis analyzes the various ways with which two RDF KBs can be compared
and how the result of this comparison can be used in order to
transform one KB to a KB semantically equivalent to the
another and vice versa. The complexity of comparing RDF KBs stems from the fact
that RDF graphs, in contrast to text, do not have a unique
serialization and RDF KBs are also enriched with the semantic of
RDFS (i.e. inferred triples). For this reason, new comparison
functions are introduced and analyzed in association with the
semantics of the change operations. Specifically, at this Thesis are
identified the pairs of (comparison function, change operation
semantics) that satisfy correctness when used for synchronizing
Knowledge Bases. Moreover, other desired properties of those pair
are investigated: small size of comparison result, semantic identity,
non-redundancy, invertibility and composition.
Finally, the algorithms for all the comparison functions are sketched
and is examined their complexity. The complexity results are verified
with experimental results.
In summary, the contribution of this work lies on the formal definition
of the comparison function and the change operation semantics, as well as
the interplay between them and the investigation of the properties the pairs
of comparison function and change operation semantics have.
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On Computing Deltas of RDF/S Knowledge Bases
