While reading the Google's Percolator paper I have noticed that Percolator supports observers - the capability to run specific logic
when data in the particular column has changed. This reminded me of triggers. Usual database triggers. As a common knowledge - something bad to use.
I will not list here the disadvantages of the triggers - they are well known. Lets look at the positive
side of them.
I realized that the triggers are almost perfect decoupling facility. It is a declarative way to set
the logic to be invoked when some row (object) in my data base (data model) has changed.
I am not aware of OO languages / frameworks which do allow such perfect flexibility. I can assume that aspect oriented
programming will allow something similar, although I doubt that it will be the match.
If you have heard of the way to achieve the same or similar capability without usage of the triggers - I would be happy to know.