The elements are the technical components of design. The lines, the shapes, the forms.
The principles are the effect of the organizing those elements. The rhythm of the lines. The emphasis of a focal point due to contrasting values. The unity of the design sensed through a color scheme.
The principles are the organization of the elements.
The composition is organization of the principles organizing the elements.
The composition is a self-contained design, but tends to gesture to something beyond itself.