外文原文：
Structure of the relational database
The relational model is the basis for any relational database management system (RDBMS).A relational model has three core components: a collection of objects or relations, operators that act on the objects or relations, and data integrity methods. In other words, it has a place to store the data, a way to create and retrieve the data, and a way to make sure that the data is logically consistent.
A relational database uses relations, or two-dimensional tables, to store the information needed to support a business. Let's go over the basic components of a traditional relational database system and look at how a relational database is designed. Once you have a solid understanding of what rows, columns, tables, and relationships are, you'll be well on your way to leveraging the power of a relational database.
Tables, Rows, and Columns
A table in a relational database, alternatively known as a relation, is a two-dimensional structure used to hold related information. A database consists of one or more related tables.
Note：Don't confuse a relation with relationships. A relation is essentially a table, and a relationship is a way to correlate, join, or associate two tables.
A row in a table is a collection or instance of one thing, such as one employee or one line Item on an invoice. A column contains all the information of a single type, and the piece of data at the intersection of a row and a column, a field, is the smallest piece of information that can be retrieved with the database's query language. For example, a table with information about employees might have a column called LAST_NAME that contains all of the employees' last names. Data is retrieved from a table by filtering on both the row and the column.
Primary Keys, Data types, and Foreign Keys
The examples throughout this article will focus on the hypothetical work of Scott Smith, database developer and entrepreneur. He just started a new widget company and wants to implement a few of the basic business functions using the relational database to manage his Human Resources (HR) department.
Relation：A two-dimensional structure used to hold related information, also known as a table.
Note：Most of Scott's employees were hired away from one of his previous employers, some of whom have over 20 years of experience in the field. As a hiring incentive, Scott has agreed to keep the new employees' original hire date in the new database.
Row：A group of one or more data elements in a database table that describes a person, place, or thing.
Column：The component of a database table that contains all of the data of the same name and type across all rows.
You'll learn about database design in the following sections, but let's assume for the moment that the majority of the database design is completed and some tables need to be implemented. Scott creates the EMP table to hold the basic employee information, and it looks something like this: EMPNO 7369 7499 7521 7566 7839 7902 ENAME SMITH ALLEN WARD JONES KING FORD JOB CLERK SALESMAN SALESMAN MANAGER PRESIDENT ANALYST MGR 7902 7698 7698 7839 7566 HIREDATE 17-DEC-80 20-FEB-81 22-FEB-81 02-APR-81 17-NOV-81 03-DEC-81 SAL 800 1600 1250 2975 5000 3000 COMM 300 500 DEPTNO 20 30 30 20 10 20 Notice that some fields in the Commission (COMM) and Manager (MGR) columns does not contain a value; they are blank. A relational database can enforce the rule that fields in a column may or may not be empty. [3]In this case, it makes sense for an employee who is not in the Sales department to have a blank Commission field. It also makes sense for the president of the company to have a blank Manager Field, since that employee doesn't report to anyone.
Field：The smallest piece of information that can be retrieved by the database query language. A field is found at the intersection of a row and a column in a database table.
On the other hand, none of the fields in the Employee Number (EMPNO) column are blank. The company always wants to assign an employee number to an employee, and that number must be different for each employee. One of the features of a relational database is that it can ensure that a value is entered into this column and that it is unique. The EMPNO column, in this case, is the primary key of the table.
Primary Key：A column (or columns) in a table that makes the row in the table distinguishable from every other row in the same table.
Notice the different data types that are stored in the EMP table: numeric values, character or alphabetic values, and date values.
As you might suspect, the DEPTNO column contains the department number for the employee. But how do you know what department name is associated with what number? Scott created the DEPT table to hold the descriptions for the department codes in the EMP table. DEPTNO 10 20 30 40 DNAME ACCOUNTING RESEARCH SALES OPERATIONS LOC NEW YORK DALLAS CHICAGO BOSTON The DEPTNO column in the EMP table contains the same values as the DEPTNO column in the DEPT table. In this case, the DEPTNO column in the EMP table is considered a foreign key to the same column in the DEPT table.
A foreign key enforces the concept of referential integrity in a relational database. The concept of referential integrity not only prevents an invalid department number from being inserted into the EMP table, but it also prevents a row in the DEPT table from being deleted if there are employees still assigned to that department.
Foreign Key：A column (or columns) in a table that draws its values from a primary or unique key column in another table. A foreign key assists in ensuring the data integrity of a table.
Referential Integrity：A method employed by a relational database system that enforces one-to-many relationships between tables.
Data Modeling
Before Scott created the actual tables in the database, he went through a design process known as data modeling. In this process, the developer conceptualizes and documents all the tables for the database. One of the common methods for modeling a database is called ERA, which stands for entities, relationships, and attributes. The database designer uses an application that can maintain entities, their attributes, and their relationships. In general, an entity corresponds to a table in the database, and the attributes of the entity correspond to columns of the table.
Data Modeling：A process of defining the entities, attributes, and relationships between the entities in preparation for creating the physical database.
The data-modeling process involves defining the entities, defining the relationships between those entities, and then defining the attributes for each of the
信息管理专业外文翻译--关系数据库的结构
