I am still not clear abt the difference between dependency and association.I have read that dependency is used to model a realtionship where changes to one party effect the other.If thats the case can "student uses the library" be modeled as a student---->library ??? in a college information application.Or will can it be modelled as an association? That leads me to another question "is this distinction between dependency and association of any value?" in my analysis.