第9章非关系型数据库NoSQL-软考吧-您身边的软考专家-www.ruankaoba.com

第9章非关系型数据库NoSQL

总题数：15题

【71-75】When we talk about a database,we must differentiate between the database（71）,which is the logical design of the database,and the database（72）,which is a snapshot of the data in the database at a given instant in time.The concept of a relation corresponds to the programming-language notion of a variable,while the concept of a relation schema corresponds to the programming-language notion of type definition. In general,a relation schema consists of a list of（73）and their corresponding domains.The concept of a relation instance corresponds to the programming-language notion of a value of a（74）.The value of a given variable may change with time; similarly the contents of a relation instance may change with time as the relation is updated.In contrast,the（75）оf a relation does not generally change.

真题详情及解析

【71-75】A database system is a collection of itererelated data and a set of programs that allow users to access and modify these data. A major purpose of a database system is to provide users with an（71）view of the data. That is, the system hides certain details of how the data are stored and maintained. For the system to be usable, it must retrieve data（72）. The need for efficiency has led designers to use complex data（73）to represent data in the database. Since many database-system users are not computer trained, developers hide the complexity from users through several levels of abstraction, to simplify users' interactions with the system. Physical level is the lowest level of abstraction that describes（74）the data are actually stored. Logical level is the next-higher level of abstraction that describes（75）data are stored in the database, and what relationships exist among those data. View level is the highest level of abstraction that describes only part of the entire database.

真题详情及解析

【71-75】The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called （71），and of relationships among these objects. An entity is a “thing” or “object” in the real world that is distinguishable from other objects. Entities are described in a database by a set of （72） . A relationship is an association among several entities. The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively. The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram, which is built up from the following components: （73） represent entity set, （74） represent attributes, etc. In addition to entities and relations, the E-R model represents certain（75） to which the contents of a database must conform. The entity-relationship model is widely used in database design.

真题详情及解析

【71-75】A transaction is an action, or a series of actions, carried out by a single user or（71）, that accesses or changes the contents of database.
A transaction should possess the four basic or so-called ACID properties:
Atomicity,The “all or nothing” property, A transaction is an（72）unit that is either performed in its entirety or is not performed at all.
Consistency. A transaction must transform the database from one consistent state to another consistent state.
Isolation. Transactions execute independently of one another. In other words, the partial effects of （73）transactions should not be visible to other transactions.
Durability. The effects of successfully completed（committed） transaction are permanently recorded in the database and must not be lost because of subsequent failure.
The four properties above, only（74）property is the responsibility of the concurrency control subsystem to ensure. It is the responsibility of both the（75）and the application developers to ensure consistency. To guarantee the Atomicity and Durability properties after a failure, a log file is needed.

真题详情及解析

【70】分布式数据库CAP理论中的A指的是（70）。

真题详情及解析

【69】分布式数据库的CAP理论指的是：对于一个分布式数据库系统，一致性、可用性和分区容错性这三个特点，最多只能满足（69）个。

真题详情及解析

【61】CAP理论是NoSQL理论的基础，下列性质不属于CAP的是（61）。

真题详情及解析

【69】以下（69）不属于NoSQL。

真题详情及解析

【63】以下NoSQL数据库中，（63）是一种高性能的分布式内存对象缓存数据库，通过缓存数据库查询结果，减少数据库访问次数，以提高动态Web应用的速度，提高可扩展性。

真题详情及解析

【70】NoSql数据库的存储模型有（70）。

真题详情及解析