假设某医院诊疗科、医生和患者各实体对应关系模式如下：诊疗科（科室代码，科室名称，电话）医生（医生代码，姓名， 科室代码）患者（病历号，姓名，年龄，性别，病情，就诊日期，医生代码）其中诊疗科允许有多部电话，则电话属性为（请作答此空）。若医生只属于一个诊疗科，并且同一天可为多位患者看病，而患者也可在不同科室治疗，患者关系模式主键是（ ）， 该关系属于（ ）问题。
- A.组合属性
- B.派生属性
- C.多值属性
- D.单值属性
正确答案及解析
正确答案
解析
本题考查关系模式和关系规范化方面基础知识。在拓展E-R图中，属性分为：（1）简单属性：原子、不可再分。（2）复合属性：可细分为多个属性部分。（3）单值属性：定义属性对于一个特定实体都只有单独一个值。（4）多值属性：一个属性可能对应一组值，如电话属性。（5）NULL属性：当实体在某个属性上没有值或属性值未知时，使用NULL值。（6）派生属性：可以从其他属性得来，如年龄属性。所以本题答案为C选项。
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