For example, one student has one teacher. But that teacher probably has a whole classroom of students, making that relationship one-to-many instead of one-to-one. It would be more accurate to say that each student has one backpack, and that each backpack belongs to one student.

You could use one line (with two arrow heads) or two lines (with one arrow each). I would also suggest that cardinality is just one kind of constraint, and the notation should reflect that. For example, the two names for the relationship could be “teaches (many)” and “is taught by (exactly one)”.

In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model) A and B in which an element of A may be linked to many elements of B, but a member of B is linked to only one element of A.

In a one-to-many relationship, one record in a table can be associated with one or more records in another table. For example, each customer can have many sales orders. In this example the primary key field in the Customers table, Customer ID, is designed to contain unique values.

Total Participation – Each entity in the entity set must participate in the relationship. If each student must enroll in a course, the participation of student will be total. Total participation is shown by double line in ER diagram.

Here are some other examples of one-to-many relationships: People-Addresses (Each person can live at one address, but each address can house one or more people.) Owners-Pets (Each pet has one owner, but each owner can have one or more pets.)

1. Total Participation- It specifies that each entity in the entity set must compulsorily participate in at least one relationship instance in that relationship set. That is why, it is also called as mandatory participation.

In another type of notation one dash is added to the relationship line at both ends. One-to-Many relation: A one-to-many relationship is represented by adding ‘1’ near the entity at left hand side of relation and ‘N’ is written near the entity at right side.

ER Diagrams are composed of entities, relationships and attributes. They also depict cardinality, which defines relationships in terms of numbers. Here’s a glossary:

An ERD represents a diagram made up mainly of rectangular blocks (for entities, or data) linked with relationships. The links between the blocks describe relations between these entities. There are three types of relationships: one-to-one, one-to-many, many-to-many.

Cardinality of Relationship: Different developers use different notation to represent the cardinality of the relationship. Not only for cardinality, but for other objects in ER diagram will have slightly different notations. But main difference is noticed in the cardinality.