The "Composed of" symbol is shown with a solid diamond."Composed of" means that the object with the diamond is the composed-of object.
Composition is a
stronger form of aggregation in which objects from the "whole" class
control the lifetime of objects from the "part" class. A pole
contains one or many crossarms. In this design, a crossarm cannot be recycled
when the pole is removed. The pole object controls the lifetime of the crossarm
Example- Suppose chicken is composed of two wings.Composed of means that these two object go together all the time.we wouldn't see one without other.If we we moving the chicken object,its composed of object go with it.If we delete this object,the composed of object would get deleted also.