[工学]Chapter2amp3amp4ClassModeling.ppt

关联类 与一个关联关系相连的类，称作关联类。关联中的每个连接与关联类中的对象相联系。 EX 电梯控制器 队列 电梯 按钮 4 队列就是电梯控制器类与电梯类的关联关系上的关联类。一个电梯控制器操纵着4台电梯，即控制器和电梯之间的实际连接有4个，每个连接都对应一个队列(对象)，每个队列(对象)存储着来自控制器和电梯内部按钮的请求服务信息。电梯控制器通过读取队列信息，选择一个合适的电梯为乘客服务。 三元关联 聚合(Aggregation) 组合(Composition) 泛化和继承(Generalization) EX EX EX 4.7 Metadata Metadata is data that describes other data. Models are inherently metadata. 元数据是描述其他数据的数据。模型本身就是元数据。 4.9 Constraints A constraint is a boolean condition involving model elements, such as objects, classes, attributes, links, associations and generalization sets. 约束是涉及各模型元素的一种布尔条件，约束可以加在对象、类、属性、链接、关联和泛化集上。 You can express constraints with natural language or a formal language such as the Object Constraint Language (OCL). Job priority {priority never increases} 4.9.1 Constraints on Objects Employee salary boss 0..1 * {salary=boss.salary} Window length width {0.8=length/width=1.5} 4.9.2 Constraints on Generalization Sets Disjoint. The subclasses are mutually exclusive. Each object belongs to exactly one of the subclasses. Overlapping. The subclasses can share some objects. An object may belong to more than one subclass. Complete. The generalization lists all the possible subclasses. Incomplete. The generalization may be missing some subclasses. EX 4.9.3 Constraints on Links 有序，值元素不唯一 sequence (list) 有序，值元素唯一 ordered 无序，值元素不唯一 bag 无序，值元素唯一 set 排列次序和唯一性 关键字 Qualified Association Class Association Multiplicity 都属于约束 政治家 政党 1 1 1 1..* 组成 领导 {子集} Person Committee 1 * * * MemberOf ChairOf {subset} 4.10 Derived Data A derived element is a function of one or more elements, which in turn may be derived. A derived element is redundant, because the other elements completely determine it. 派生元素是可以由一个或多个元素产生出来的元素。派生用于描述某种事物的产生规则。 一般来说，约束和派生能应用于任何模型元素，但最常用于属性、关联、继承、角色和时间。派生元素的表示是在元素名前面加一条斜线。 Person CurrentDate birthdate /age {age=currentdate-birthday} 商品 成本价格 销售价格 /利润 {利润=销售价格-成本价格} 4.11 Packages A package is a group of elements (classes, associations, generalization and lesser package) with a com