华南农业大学期末考试试卷(a)2006数据库答案.docVIP

华南农业大学期末考试试卷（A卷）d 2006　学年第一学期　 考试科目： 数据库原理与方法 考试类型：（闭卷）　　　 考试时间： 120 分钟 参考答案： Question 1: A database-management system (DBMS) is a collection of interrelated data and a set of programs to access those data. Metadata is data about data. The E-R data model is a widely used data model for database design. It provides a convenient grapical representation to view data, relationships, and constraints. A superkey of an entity set is a set of one or more attributes that, taken collectivly, allows us to identify uniquely an entity in the entity set. Such minnimal superkeys are called candidate keys. A data-manipulation language (DML) is a language than enables users to access or manipulate data. A data-definition language (DDL) is a language for specifying the database schema and as well as other properties of the data. Transactions are required to have the ACID properties: atomicity, consistency, isolation, and durability. Atomicity ensures that either all the effects of transaction are reflected in the database, or none are; Consistency ensures that, if the database is initially consistent, the execution of the transaction leaves the database in a consistent state. Isolation ensures that concurrently executing transactions are isolated from on another. Durablity ensures that, once a transaction has been committed, that transaction’s udpates do not get lost, even if there is a system failure. It is a state where neither of these transactions can ever proceed with its normal execution. Concurrency schedule consists of a sequence of instructions from various transactions which run concurrently. A unique fixed timestamp is associated with each transaction in the system. The timestamp of the transaction determine the serializability order. The most widely used structure for recording database modifications is the log. The log is a sequence of log records, recording all the update activities in the database. Question 2: a. b: Relation schemas: factory(name, director