add personal-understanding about  model has-a or is-implementation-in-terms-of through composition
add personal-understanding about  model has-a or
is-implementation-in-terms-of through composition

ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study,ASMlover/study