Recently Web services based on the HTTP and XML technology have become widely used, and application programs or mashups integrating such services have also proliferated. In order to support the integration process, we have developed a tool to convert user-defined function specifications written in XML to the corresponding user-defined functions loadable to PostgreSQL, an extensible relational database management system. With this conversion layer provided by the tool, multiple Web services and relational databases can be integrated in SQL, and therefore, integrated applications or mashups can be built quickly without being bothered by variety of Web service interfaces defining the calling sequences and result data types. Moreover, even if one of the Web service providers that a particular mashup depends on changes its service specification, the application does not need to be modified accordingly, when the corresponding function's calling interface remains intact by changing the specification of the function body. This property which we refer to as Web service independence is quite important since Web service interfaces may change without any previous notices, and so some management methodology is needed for mashups.
['Yoshihiko Ichikawa', 'Yuuki Matsui', 'Minoru Tanaka']
SQL as a mashup tool: design and implementation of a web service integration approach based on the concept of extensible relational database management systems