We show several properties of the abstract interpretation settings
regarding relationships between precision of semantic operators and
abstract domains composition.
Then, we apply these results to the framework for logic programs
introduced in [CominiLM95], extended with the new class of
operational observables. We prove that the classes
of perfect, denotational and operational observables are complete
lattices and we discuss some problems that arise studying them. 
  Finally, we show how to use functional dependencies to
systematically derive new domains in which our semantic operators
enjoy desired precision properties.