watch list on fields implementation

[usmle Prep]

We are planning to create a watch based on some fields
in bugs database.For time being they are fields of
"bugs" table.It may be extended later.
Did anyone implement it already?
It should work like this: Say target_milestone field
in bugs table changes, then a particular group of
people should be notified .Please let me know if it is
already there.
Thanks a lot,
Srikant

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