when object library is attached to a form complete object library are compile/used in compilation assume that object library has some objects like 1 2 3. But my form don't use 1 2 & 3 all it uses only 1 2. But still ur form contain 1 2 3 all because the object library is attached.
when pl/sql is attached to a form it picks up only those source from pl/sql library which is used in the form. other sources are not loaded onto the memory.
Object libary can be used to define the standard layouts like fonts size colour etc for the item being created on the form.
pl/sql libarary can contain only the pl/sql codes which can be used for standadizing the validations etc.
