A RDBMS is a system that organizes data into tables called relations, which are further organized into columns (fields) and rows (often called tuples). The relational model allows data to be queried in a nearly unlimited number of ways, making it great for sorting through large volumes of data. It’s important to pick a SQL developer who’s experienced with the particular set of web technologies you plan to use to support your app. Common SQL dialects include PL/SQL for Oracle, T-SQL for MS SQL, and JET SQL for MS Access. Look up any particular dialects used for your chosen RDBMS.