Update through views: a possible approach

(In draft as at early February 2017.)

It is assumed the reader is familiar with the topic of update through views. 'View' is the usual term in the within database discussions, as for example in SQL. The ttm term is 'Virtual relvar'. The updating through views is discussed, for example, in both DTATRM and DBE.

Background

Update through views is a regular discussion topic on the ttm forum. And a regular topic for Chris Date, co-author of The Third Manifesto. He has published many treatments, since particularly a series of articles (with David McGoveran) 1994 [published on dbdebunk]. Arising from that 1994 treatment also was the Principle Of Orthogonal Design, aimed at making update through views more tractable. McGoveran also continues to publish on the topic, also emphasising Orthogonal Design. The topic has also been much discussed on older forums, such as comp.database.theory.

There are a wide variety of opinions on the desirability, possibility and practicability of update through views:

• Those who assert update is possible through all views, and the mechanisms merely need refining.
• Those who prescribe update should be possible through all views "that are theoretically updatable".