30个术语解析

DBMS

Database management system is a collection of interelated data and a set of programs to access those data.

Super key

Superkey is one or more attributes in a relation that can identify uniquely every entity in an entity set

Candidate key

Such minimal superkey is called candidate key.

Primary key

The candidate key that chosen by database designer to identify uniquely an entity.

Foreign key

a relation schema r1, include a attribute that is the primary key of another relation schema r2,we call it is a foreign key of r1 from r2.

Database schema

The overall design of database

Data independence

Data independence to program.include physical data independence and logical data independece

Data model

一个描述数据、数据联系、数据语义以及数据约束的工具集合。

E-R model

实体关系模型广泛应用于数据库设计。它提供方便的图形化描述方法，描述数据、关系和约束。

Data dictionary

Data dictionary stores metadata about the structure of database,in particular schema of database.

View

视图不是逻辑模型的一部分，而是用户可见的虚关系。

Schedule

事务的执行顺序称为一个调度。表示事务的指令在系统中执行的时间顺序

Functional dependence

Consider a relation schema R , a in R,b in R

for every tuples t1 , t2

if t1[a]=t2[b] then t1[b]=t2[b]

we can say that there is a functional independence a->b

Consistency

Transaction

Transaction is a unit of program excution that access or possibly update various data items.

ACID

Transaction has four properties:

Atomicity , consistency , isolation , durability

Deadlock

Checkpoints

Serializable schedule

如果一个调度和一个串行调度是等价的，则称这个调度是可串行化调度。

SQL

结构化查询语言structure query language

DDL

Data definition language 定义数据库的模式和其他数据特性。

DML

Data manipulation language 使得用户可以访问和操纵数据

Outer join

Natural join

1NF,2NF,3NF,BCNF

Log

Log是日志记录的序列，记录数据库的所有更新活动。

Metadata

Metadata is data about data

Data inconsistency

The various copies of the same data may no longer agree.

Relational schema

Relational schema is logical design of a relational table or a relation.

Relational instance

Relational instance is the content of a relation at a given instance in time.

concurrency schedule

concurrency schedule is consist of a squence of instructions from various transaction which run concurrently.

timestamp

a unique fixed timestamp is associated with each transaction in the system.the timestamp of transaction determine the serializability order.

Null value

Null value indicate absence of information in an attribute.