> On 1 May 2015, at 19:51, Robert Haas <robertmh...@gmail.com> wrote: > > On Thu, Apr 30, 2015 at 6:36 PM, Joe Wildish > <joe-postgresql....@elusive.cx> wrote: >> I’m wondering if there are other people out there working on implementing >> SQL ASSERTION functionality? >> >> I’ve recently spent a bit of time looking to implement the execution models >> described in “Applied Mathematics for Database Professionals” by Toon >> Koppelaars and Lex de Haan. I’ve gotten as far as execution model 3 and am >> now looking at deriving polarity of involved tables to do EM4 (described in >> some detail in “Deriving Production Rules for Constraint Maintenance”, Ceri >> & Widom, VLDB Conference 1990, p555-577). EM5 & EM6 look rather more >> difficult but I’m intending to try and implement those, too. >> >> If there are other people working on this stuff it would be great to >> collaborate. > > I don't know of anyone working on this. It sounds very difficult.
The book I mention details a series of execution models, where each successive model aims to validate the assertion in a more efficient manner than the last. This is achieved by performing static analysis of the assertion's expression to determine under what circumstances the assertion need be (re)checked. Briefly: EM1: after all DML statements; EM2: only after DML statements involving tables mentioned in the assertion expression; EM3: only after DML statements involving the columns mentioned in the assertion expression; EM4: only after DML statements involving the columns, plus if the statement has a “polarity” that may affect the assertion expression. “Polarity" here means that one is able to (statically) determine if only INSERTS and not DELETES can affect an expression or vice-versa. EMs 5 and 6 are further enhancements that make use of querying the “transition effect” data of what actually changed in a statement, to determine if the assertion expression need be validated. I’ve not done as much reading around this topic yet so am concentrating on EMs 1-4. I agree it is a difficult problem but there are a fair number of published academic papers relating to this topic. The AM4DP book draws a lot of this research together and presents the executions models. I may start writing up on a blog of where I get to, and then post further to this list, if there is interest. Regards. -Joe -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
