5.2 领域模型建模指导
敏捷建模Agile Modeling – 类图的草图
– 是否利用工具建模
创建领域模型的目的是快速地理解关键的概念，并在涉众之间交流
the purpose of creating a domain model is to quickly understand and communicate of the key concepts 完美不是目标 Perfection is not the goal
是否利用工具，酌情 For tool, may or not
报告性的、或者总结性的对象，是否定义为概念 Report Objects / summary object : to be an concept
E.g. Include 'Receipt' in the Model?
In general, showing a report of other information in a domain model is not useful since all its information is derived or duplicated from other sources
This is a reason to exclude it
On the other hand, it has a special role in terms of the business rules:
It usually confers the right to the bearer of the (paper) receipt to return bought items (顾客退货的凭据)
This is a reason to show it in the model Guideline
构建领域模型，类似地图制作
使用现有的名词 Use the existing names in the territory
For example, if developing a model for a library, name the customer a "Borrower" or "Patron” the terms used by the library staff
剔除掉无关的、或者超出范围的一些特征 Exclude irrelevant or out-of-scope features
例如，在课程的案例“大富翁游戏 Monopoly”，第一次迭代中，有些概念,如各类卡 片 cards (“免进 监狱Get out of Jail Free” card) 暂不考虑，所以就不显示“Card”
不需要额外增加没必要的概念！Do not add things that are not there
如何对非真实世界的概念建模
有些软件系统着眼于解决领域问题，但是在现实中或者业务中很少有概念与之对应
例如，电信领域“交换机”相关的概念
消息、连接、端口、对话、路由、协议 Message, Connection, Port, Dialog, Route, Protocol
经常容易出错的选择：Attributes vs. Classes ，原则：
如果认为某概念类X不是现实世界中的数字或文本，那么X可能是概念类而不是属性
如果符合下列条件，可能是一个类
有很多元素构成 Composed of multiple elements (has attributes-states)
有一些操作、行为 There are operations (behavior)
有数量单位 Has units of quantity
例如
Store ?
consider the domain of airline reservations. Should destination be an attribute of Flight, or a separate conceptual class Airport ?
对一些描述‘Description’性质的概念建模
A description class contains information that describes something else
For example, a ProductDescription that records the price, picture, vendor, and text description of an Item
为什么单独作为概念类
Where to find product information when they were sold out 商品卖光了之后， 到哪里去找商品的信息 呢
Each Product of same type has its product description information, is there any problem 如果每一个 同类产品的信息都含有产品描述，有什么问题吗
Repeat, redundant, inconsistency, and a waste of storage space 重复、累赘，不 一致、浪费存 储空间
定义成“描述”类的原则
如果描述内容独立于对应 的事物 ，如产品、产品 描述
如果删除对象的同时删除 了描述，而该描述还需要 继续维护
为了减少重复或者更清晰
