Set Comparison in Relational Query Languages

Abstract

Today’s de facto database standard, the relational database, was conceived in the late 1960’s by Edgar F. Codd at IBM. The relational data model offered the user a logical view of the data that was shielded from consideration of how the data would, in fact, be physically organized in storage. This feat was accomplished in large part by the introduction of relational query languages that would specify the desired set of records in a non-procedural fashion. In contrast to the prevailing record-at-a-time, loop-oriented, procedural query languages of the hierarchical and network database management systems, relational query languages were set-oriented in that they would operate on sets of records (i.e., relations or tables) at-a-time in order to produce the desired set of output records. Codd introduced both a relational algebra and a relational calculus as a basis for dealing with data in relational form. Indeed, he defined what the first relational language was: Data Sublanguage Alpha (Codd, 1971).