扩展数据字典与ER图

Question

这是一个任务的问题。有人能帮帮我吗？

准则

1. 包含适当数据项和每个数据项的所有相关详细信息的广泛数据字典。
2. 包含使用的适当表和约束的广泛ER图。数据字典中的所有数据项都反映在表中。

给出的数据字典

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终于问了我的问题

1. 如果已经有了数据字典，我应该创建一个广泛的数据字典吗？
2. 我下面做的对吗？

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Answer 1

你可能会明白，我无法解决你的任务:总有一天，你可能会为我将要使用的飞机或医疗设备编写任务关键系统，我想确保你拥有所需的所有技能;-)

但这里有一些提示可以指导你：

1. 提供的数据字典不够广泛。所以我想你得把丢失的细胞填满。例如：

- if every employee belongs to a department, do you think that `Employee.Department_id` is nullable ?
- if several employees may belong to the same department department,  do you think that `Employee.Department_id` is unique ?
- What with the descriptions and examples?

1. 您的第二个ERD使用陈表示法。这些都很好地显示实体、关系、属性。它们不是用来复制表的。虽然乍一看似乎是正确的，但仍需作出一些改进：

- the cardinalities between the entities and relationships are definitively missing.
- Primary key attributes should be underlined.
- Foreign keys are usually not shown, since they are deduced from the relationships and cardinality.

1. 您的第一个ERD使用巴克氏符号。虽然它还显示实体、关系和属性，但它的目的是将实体和属性映射到表和键。在这方面，考虑到您的赋值要求，最好是显示字典的所有属性。需要作出一些改进：

- Primary keys are well identified.  But there are problems with the foreign keys:  put a `FK` only in front of the columns identified as foreign key in data dictionary.
- between the entities,  you should use the right symbols to reflect the cadinality (simple bar on the side where one item corresponds,  crowfoot bars on the side where several items corrspond, and o on the side where there could be no item)
- While it is possible to simply show the relationship between entities by connecting them to the table header or the bottom line, in a detailed diagram showing all the field,  it is better to graphically connect the boexes at the level of the primary and foreign keys that implement the relationship.