Semantics Preserving SQL-to-SPARQL Query Translation for Left Outer Join
BAHAJ Mohamed, Soussi Nassima
International Journal of Web Applications, Vol. 9, No. 4, 2017.
DOI: 
Link: http://www.dline.info/ijwa/fulltext/v9n4/ijwav9n4_3.pdf
Abstract:
Despite the emergence of the Semantic Web and its performance, relational databases are still the most used for data manipulation, making the mapping of the relational world to the semantic world a very pertinent research topic to fill
the gap between these two heterogeneous systems and ensure better semantic interoperability without physical transformation
of data represented with different syntaxes. Regarding the transformation of SQL queries to SPARQL queries semantically
equivalent, several algorithms have been developed to ensure this conversion; unfortunately, most of these algorithms have
shortcomings and weaknesses in the consideration of the Left Outer Join commands in SQL queries. This problem has
motivated us to write this paper so as to remedy this lack. Our main contribution is as follows: (a) establish an effective
semantic transformation algorithm for Left Outer Join commands (in their simple and nested structures) to their equivalent
in the SPARQL language, (b) integrate this result to RETRO (A Framework for Semantics Preserving SQL-to-SPARQL Translation) in order to have a richer algorithm that contribute to treatment of a maximum of SQL commands.