buffer properti object model element recept buffer properti sb buffer append queri state model facad queri model element properti sb append queri oper signal peer uml type hierarchi share attribut root leaf specif concurr share specif oper model facad root model element properti sb append root model facad leaf model element properti sb append leaf recept model facad concurr model element properti sb append model facad model facad concurr model element properti sb append properti sb length properti sb delet properti sb length properti sb length remov properti sb append properti sb buffer properti sb 