ERD stands for Entity Relationship Diagram. It is one of the most important analysis diagrams for designing a database.
In relational databases, the data is split up into tables instead of writing it all out in a single line or record. This removes some of the problems often encountered in building a database. The tables are linked together by the primary key of one table being present as what is called a foreign key in another table.
For example, a teacher may teach many students, but we do not want to repeat the teacher's name, telephone number, room number every time we record a new student and their teacher. So only the identifying primary key of the teacher is included in the student record.
This is illustrated in an ERD by a line joining the two tables student and teacher. There are several different styles for drawing an ERD, but they all have a way of showing which table's entries are used as the foreign key in another table.
Many database designers start by drawing an ERD using their experience to analyse what the likely relationships are, before even listing the attributes the table will store.
The ERD summarises the database structure.
In relational databases, the data is split up into tables instead of writing it all out in a single line or record. This removes some of the problems often encountered in building a database. The tables are linked together by the primary key of one table being present as what is called a foreign key in another table.
For example, a teacher may teach many students, but we do not want to repeat the teacher's name, telephone number, room number every time we record a new student and their teacher. So only the identifying primary key of the teacher is included in the student record.
This is illustrated in an ERD by a line joining the two tables student and teacher. There are several different styles for drawing an ERD, but they all have a way of showing which table's entries are used as the foreign key in another table.
Many database designers start by drawing an ERD using their experience to analyse what the likely relationships are, before even listing the attributes the table will store.
The ERD summarises the database structure.
