How many relational databases have there been? How many are now extinct? How are they related to one another? These questions are all answered in a single chart.
Click for larger image (pdf)
This complicated family tree of relational databases has been created by the Hasso-Plattner Institut, part of the University of Potsdam, Germany. It resembles a map of a metro system but the lines are time-lines with the symbols marking milestones in each product's life cycle; date of publication, subsequent versions, acquisitions and discontinuations when a product reaches the end of its line.
What is interesting is the way in which products branch and merge.
The RDBMS Genealogy chart clearly visualizes the history of relational databases showing that Ingres was the very first RDBMS and that circa 1980 Postgres was created as a branch of it and that SQL Server is a direct descendant of Sybase. It also carries encyclopedic value introducing people to products previously unheard of. What is also interesting is that you can perhaps discern the future of the RDBMS's by observing that, a few years after the millennium many Analytics engines like Vectorwise, Infobright or AsterDatabase, came on the scene. something that identifies the current trend.
Where, you might ask are Hbase, MongoDB, CouchDB and the other NoSQL databases - well as they are not relational databases they are not part of the landscape.
Personally I liked the addition of the geographical feature of rivers, with Relational Creek flowing into Codd River.
That's a nice tribute!