Dr. Codd's theoretical work ton the relational model in 1969-70 was followed by several research prototypes in various IBM labs. These included the Peterlee Relational Test Vehicle in the United Kingdom and the Extended Relational Memory in Cambridge, MA. At the same time, a parallel effort to define a language which would realize the features of Dr. Codd's relational model was underway at the Santa Teresa Research Labs in San Jose, CA. The product, of this research, SEQUEL-XRM, was announced in 1974. This was followed by a revised version, SEQUEL/2, in 1976, which later became SQL. The advent of SEQUEL led to the development of a prototype relational DBMS for the VM/CMS environment. The prototype was called Sys­tem R and it became operational in 1977. System R paved the way for the introduction, in 1981, of SQL/DS, IBM's RDBMS for the small systems environment. SQL/DS runs under DOS/VSE and VM/CMS operating systems and is still marketed today. SQL/DS was followed by DB2 in 1984. The main difference between SQL/DS and DB2 is that SQL/DS has a small systems orientation while DB2 is designed for the large systems environment.

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