With active research on Web ontology, various storages and ontology query languages have been introduced. The most representative query language for Web ontology is SPARQL which have been developed by W3C, and most storages are based on relational database. Under such a situation, the necessity of SPARQL-to-SQL translation algorithm development becomes issued. Even though several translation algorithms have been proposed, there still remain the following problems: (1) They do not fully support SPARQL statements. It means that they cannot translate SPARQL query statements with UNION or FILTER to SQL; (2) The algorithms are dependent on a specific storage model and it requires much cost for modification and verification. In this paper, we focus on the second issue, and a system model for independent use upon storage structures of an algorithm is proposed. The system model guarantees independency between translation algorithms and storages, and it improves application and usability of a translation algorithm.