資料庫--訓

最近蛋痛，把幾年前學的雙拼又拿起來。打字的速度顯著下降！

• 1. Developing a data model
• Attribute, class, or relationship?
• Here are some examples of questions to help you decide. Might I want to select objects based on the value of an attribute? If the answer is yes, consider introducing a class for that information(create a grede class).
  我這裡有一些案例可以幫助你做出決定。我是否可能會根據一個屬性的值去選擇一個對象？例如，你是否可能會根據年級去選擇一個球隊？如果是，考慮為該信息引入一個表（類）(一個年級表)。
• Am Ilikely now or in the future to store other data about this information? For example, might I want to keep additional information about the captain: phone, address, and so on? If yes, consider introducing a class.

  我是否可能現在或則在未來需要存儲該信息的其他數據。比如，我是否準備保存隊長的其他信息：電話、地址等等。如果想，考慮建立一個表（類）。

• Am I storing (or should I be storing) such information already? For example, the information about a captain is the same or similar to infromation about members. Consider a relationship between existing class.
  我是否正在（或則應該）存儲這些信息？比如，隊長的信息和隊員的信息是很相似的。考慮在已經存在的表之間建立一個關係。

• More than one relationship between two classes兩表之間不止一個關係
• Consider more than one relationship between two classes if there is different information involving both classes. For example, a member might play for a team, captain a team, manage a team, and so on.
  如果兩表間都有不同的數據時就需要考慮多個關係。比如，一個球員可能效力於，管理，帶領一個球隊。

• Consider self relationships自身關係
• Objects of a class can be related to each other. For example, members sponsor other members, people are parents of other people. 表的對象之間可以相互關聯。比如，球員贊助其他球員，百姓是百姓的父母。

• Different routes between classes 表之間的不同路徑
• Check wherever there is a closed loop to see whether the same information is being stored more than once.
  檢測關係路徑是否包含閉路以便發現相同的信息是否被存儲了多次。
• Check to ensure you are not inferring more than you should from a route; that is, look out for fan traps where a class is related to two other classes and there is a cardinality of Many at both outer ends.

  檢測儀確保你不會獲取到你不應該得到的數據；即小心Fan Trap，一個表和兩個其他表相關，關係外側的兩個類的集合都包含多個元素。

• Check to ensure a path is available for all objects; that is look ourt for chasm traps(are there optional relationships along the route?).
  確保一條關係路徑可以通向所有對象；即Chasm trap問題。

• Information dependent on objects of more than two classes
• Consider introducing a new class where you need to know about combinations of objects from three or more class simultaneously; for example, which member played for which team in which match?
  當你需要同時從三個或以上的表中獲取一個組合對象時，考慮引入一個新的表。比如，那個球員效力於某個球隊，參加了某場比賽？
• Any attributes inn the class must dependon particular combination of objects from each of the participating classes; such as, what do I need to know about a particular member playing on a particular team in a particular match?
  一個新表中的任一個屬性必須依賴每一個參與表的對象的特殊組合；比如，某個特定球員效力於某個特定的球隊，參與了某場比賽，對此我需要了解什麼？
• Consider what information might be pertinent to two objects form pairs of the contributing classes; for example, what do I need to know about a particular member and a particular team independent of any match?

  考慮什麼信息可能成為兩個表之間的中心；比如，對於獨立於球賽的一個特定球員和一個特定球隊，我需要知道什麼？

推薦閱讀：