VF复习资料

Chapter 11.What are the applications of database systems?什么是数据库应用系统∙Banking∙Airlines∙Universities(for example:Add new students, instructors, and courses. Register students for courses, and generate class rosters. Assign grades to students,compute grade point averages (GPA) and generate transcripts. ) ∙Credit card transactions∙Telecommunications∙Sales∙Manufacturing∙Human resources•银行•航空公司•大学（例如：添加新的学生，教师，以及课程。

学生注册课程，并产生的班级花名册。

计算指定年级的学生，平均成绩（学分）和产生的成绩单。

）•信用卡交易•电信•销售•制造•人力资源3.explain the terms: instance schema entity relationship attributes DDL DML DBA DBMS and query.3.explain术语：实例架构实体关系属性数据库管理员数据库和查询数据操纵语言。

Instance: The collection of information stored in the database at a particular moment is called instance of the database.实例：收集的信息存储在数据库中某一特定时刻被称为数据库实例。

Schema: The overall design of the database is called the database schema.架构：整体设计的数据库被称为数据库模式Entity: An object in the mini world about which information is to be stored.实体：物体的迷你世界哪些资料存储Relationship: A relationship is a connection between two or more entity sets关系：一个关系之间的连接两根或两根以上的实体集Attribute: A property or feature of an entity (or relationship)属性：一个属性或特征的一个实体（或关系）DDL: We specify a database schema by a set of definitions expressed by a special language called a data-definition language介绍：我们指定一个数据库模式的一套定义表达的一种特殊的语言称为数据定义语言DML: Data-manipulation language (DML) is a language that enables users to access or manipulate data as organized by the appropriate data model数据操纵语言数据操纵语言（语言）是一种语言，使用户能够访问和操纵数据组织的适当的数据模型DBA:A database administrator,a person who has such central control over the system.数据库：数据库管理员，一个人有这样的中央控制系统。

DBMS: A database- management system (DBMS) is a collection of interrelated data and a set of programs to access those data.数据库管理系统数据库管理系统（数据库管理系统）是一个相关的数据集合和访问这些数据的程序。

Query: A query is a statement requesting the retrieval of information.查询：查询语句请求的信息检索。

Chapter 21．What are the different types of attributes? Explain with examples. 什么是不同类型的属性？举例说明Attribute Types: An attribute, as used in the E-R model, can be characterized by the following attribute types.属性：一个属性类型，如使用在E - R模型，可以通过以下属性类型1. Simple(Eg. cust-street) : with no further subsets简单的（例如cust-street）：没有进一步的子集2. Composite(Eg. name, which includes FN,LN,MN): with further subsets3. Single (Eg. loan-number) : which takes just one value4. Multi-valued (Eg. phone-number): This takes more values. A customer may have many phone numbers5. Derived (Eg. age derived from DOB): the age can be derived from date-of-birth attribute6. Null (Eg. middlename, one may not have middle name): attributes which takes null values or which are “not-applicable”2。

复合材料（如姓名，其中包括蛋白，蛋白，锰）：进一步的子集3。

单（如loan-number）：只需要一个值4。

多值（例如，电话号码）：这需要更多的价值。

客户可以有多个电话号码5。

来源（例如，年龄从出生日期）：年龄可以从日期的出生属性6。

空（如特徵，可能没有中间名）：属性，以空值或是“not-applicable”2. Describe the terms (a) Super key, (b) Candidate key, and (a) Primary key with an example. 。

描述的条件（一）超键，（二）候选键，和（一）主键的例子。

• A superkey is a set of one or more attributes that, taken collectively, allow us to identify uniquely an entity in the entity set. For example, the customer-id attribute of the entity set customer is sufficient to distinguish one customer entity from another. Thus, customer-id is a superkey. Similarly, the combination of customer-name and customer-id is a superkey for the entity set customer. The customer-name attribute of customer is not a superkey, because several people might have the same name. • The concept of a superkey is not sufficient for our purposes, since, as we saw, a superkey may contain extraneous attributes. If K is a superkey, then so is any superset of K. We are often interested in superkeys for which no proper subset is a superkey. Such minimal superkeys are called candidate keys.• It is possible that several distinct sets of attributes could serve as a candidate key. Suppose that a combination of customer-name and customer-street is sufficient to distinguish among members of the customer entity set. Then, both {customer-id} and{customer-name, customer-street} are candidate keys. Although the attributes customer-id and customer-name together can distinguish customer entities, their combination does not form a candidate key, since the attribute customer-id alone is a candidate key.• We shall use the term primary key to denote a candidate key that is chosen by the database designer as the principal means of identifying entities within an entity set. In theUnited States, the social-security number attribute of a person would be a candidate key.一个超码是一个或多个属性设置，采取集体，使我们能够确定一个独特的实体在实体集合。