Relational Model/Tasmania (RM/T) was published by Edgar F. Codd in 1979 and is the name given to a number of extensions to his original relational model (RM) published in 1970. The overall goal of the RM/T was to define some fundamental semantic units, at "atomic" and "molecular" levels, for data modelling. Codd writes: "the result is a model with a richer variety of objects than the original relational model, additional insert-update-delete rules and some additional operators that make the algebra more powerful."

RM history

Between 1968 and 1988 Codd published over 30 papers on the relational model (RM) - the most famous of which is his 1970 paper. Up to 1978 the papers describe RM Version 1 (RM/V1). In early 1979 Codd first presented some new ideas, called RM/T ('T' for Tasmania), at an invited talk for the Australian Computer Science Conference in Hobart, Tasmania. Later that year the ACM journal published a paper on RM/T, in which Codd acknowledges the influence of Schmid & Swensen (1975) and Wiederhold (1977). A later version of RM/T (we shall call it here "RM/D") was described by Chris Date in Date (1983) in which Date and Codd improved and refined RM/T, adding an entity type called designative. Although Codd writes nothing about this new type, Date offers a rationale in Date (1983, page 262). Date revised this 1983 article in Date (1995), which additionally compares the RM/T model with the E/R model. Following a disappointing uptake of RM/T by the database industry, Codd decided to introduce the RM/T model more gradually. He planned to release a sequence of RM versions: RM/V2, RM/V3 etc. each time progressively including some of the ideas of the original RM/T into the new version. Perhaps this explains why there is no obvious mapping of concepts between RM/T and RM/V2. For example, there is no reference to associative or designative entity types in Codd's 1990 book that defines RM/V2. On the other hand, the book extends and builds on the existing body of query language issues, many of which were addressed by Codd in several papers throughout the 1980s.

Summary of RM/T

Introducing some of the new concepts of RM/T:

RM/T today

There is little mention of RM/T today and no articles have appeared recently. Peckam and Maryanski (1988) wrote about RM/T in their study of semantic data models. Codd published his book in 1990 but wrote nothing more about RM/T. RM/V1 and RM/V2 have a chapter each in Date and Darwen (1992) and the Date (1983) article was updated in (1995) and now contains a long overdue comparison of the E/R model and RM/T. Date's most recent reflections can be found on the Web at Date (1999), The Database Relational Model (2001) and Date on RM/T (2003). RM/T contributed to the body of knowledge called semantic data modeling and semantic object modeling and continues to influence new data modellers. See the paper by Hammer and McLeod (1981), the book by Knoenke (2001) and implementation by Grabczewski et alia (2004).