Database management systems have been around for a long time... a lot longer than the relational model and SQL. Of course, SQL systems (which are based on relational concepts), are the primary DBMSes implemented in large corporations today.
The links on this page highlight some of the more popular non-relational database products that are available.
Let’s take a look at some of the more popular non-relational DBMS product offerings:
One popular non-relational DBMS type is the hierarchical DBMS. Popularized in the 1960’s, IBM’s IMS is the most popular example of such a DBMS. IMS is still used in many of the world’s largest and most performance sensitive applications.
If interested, you can find a nice primer on IMS here.
Other Non-Relational DBMSes
Adabas - Software AG’s inverted list DBMS
Cache - Intersystem’s object DBMS
IDMS - CA’s network/CODASYL DBMS
U2 - Rocket Software’s multi-value DBMS
Versant Object Database - its name says it all
There are many other types of database systems, too.
Some are more “relational”-like than others.
Some are completely different and if the only thing you know is SQL, don’t attempt to use these DBMSes without some help.
Dr. E.F. Codd
Inventor, Relational Model
What about NoSQL database systems? more>
Yet another trend in database systems is occurring right now – NoSQL databases.
IBM’s IMS Family web site