• Stage
    ○ stage = (static)properties + (dynamic)value,usually
• Behavior 
    ○ denote obeject acts + reacts
    ○ denote as outway visiable activity
    ○ 1⃣️ Operation
        § Modifier
        § Selector
        § Iterator
        ---
        § Constructor
        § Destructer
    ○ 2⃣️ Roles and Responsibilities
        § Responsibilities = express one purpuse of an object(对象的一种目标) + it's place in the system（对象在系统中的位置）
        § Role：dynamic + mutually exclusive
• Identify
    ○ ~: The unique identity(neccesary the name) of each object is preserved over the lifetime of the object, even when it's state is changed.
    ○ 包括变量名和指针名
• The relationship of objects
    ○ Links
        § The pysical or conceptual connection(物理或概念上的联系) of two objects
        § A link denote the specifc association(具体的关系)
        § Usually unidrectional(单箭头)，sometimes bidirectional(双箭头)
        § In a link, one object can act as these roles:
            □ Controller
            □ Server
            □ Proxy
        § 1⃣️ Visibility
            □ The two endpoints in a link can see each other
        § 2⃣️ Sychronization
            □ Whenever an object passes a message to anthor across a link, the two objects are said to be synchronized
            □ Sequatial
                ® Passive object linked to a active object at a time
            □ Guarded
                ® With the multiple threads control, active clients must collaborate（协作） to achive mutual exclusion(互斥)
            □ Concurrent
                ® With the multiple threads control, the supplier(服务提供者) guarantees() mutal exclusion

    ○ Aggregation

Denote a whole/part relationship(->整体/部分层次结构)