What are the rules for converting an ERD into tables?

The rules for converting an ERD into tables involve creating tables for entities, defining primary keys, and establishing relationships.

When converting an Entity-Relationship Diagram (ERD) into tables, the first step is to create a table for each entity in the ERD. Each entity becomes a table in the database. The attributes of the entity become the columns of the table. For example, if you have an entity called 'Student' with attributes 'Name', 'Age', and 'ID', you would create a table called 'Student' with columns for 'Name', 'Age', and 'ID'.

The next step is to define the primary key for each table. The primary key is a unique identifier for each record in the table. In the ERD, the primary key is usually indicated by underlining the attribute. If an entity has a composite primary key, meaning the primary key is made up of more than one attribute, then all those attributes become part of the primary key in the table.

The third step is to establish the relationships between the tables. In the ERD, relationships are represented by lines connecting the entities. The type of relationship (one-to-one, one-to-many, or many-to-many) determines how the relationship is implemented in the tables. For one-to-one and one-to-many relationships, a foreign key is added to the table on the 'many' side of the relationship. The foreign key is a column that contains the primary key of the related record in the other table. For many-to-many relationships, a junction table is created. The junction table contains foreign keys to both related tables.

Lastly, the cardinality and optionality of the relationships are also considered. Cardinality refers to the number of instances of an entity that can be associated with each instance of another entity. Optionality refers to whether an instance of an entity must be associated with an instance of another entity. These are represented in the ERD by the symbols at the ends of the relationship lines and are implemented in the tables through constraints.

In summary, converting an ERD into tables involves creating tables for entities, defining primary keys, establishing relationships, and considering cardinality and optionality.