Many-to-one: When more than one instance of an entity is linked with the relationship, it is termed as 'N:1'.One-to-many: When more than one instance of an entity is related and linked with a relationship, it is termed as '1:N'.One-to-one: When only a single instance of an entity is associated with the relationship, it is termed as '1:1'.All the entities (rectangle-shaped) participating in a relationship get connected using a line. It is to be noted that multi-valued attributes are represented using double ellipse like this:Ī diamond-shaped box represents relationships. Every elliptical figure represents one attribute and is directly connected to its entity (which is represented as a rectangle). What are Attributes?Īttributes are the properties of entities that are represented using ellipse-shaped figures. A relationship of degree two is called binary degree (relationship). In the above-figured example, "Branch has a staff", there is a relationship between two participating entities. The number of participants involved in a relationship type is termed as the degree of that relationship. The entities occupied in a particular relationship type are referred to as participants in that relationship. Here is a diagram showing how relationships are formed in a database. Each relationship type is given a name that describes its function. Diagrammatic Representation of Entity TypesĮach entity type is shown as a rectangle labeled with the name of the entity, which is usually a singular noun.Ī relationship type is a set of associations between one or more participating entity types. Entity occurrence: A uniquely identifiable object of an entity type.An entity type has an independent existence within a database. The basic concept of the ER model is the entity type that is used to represent a group of 'objects' in the 'real world' with the same properties. Entity type: It is a group of objects with the same properties that are identified by the enterprise as having an independent existence.ER modeling is an important technique for any database designer to master and forms the basis of the methodology. Then database model designers can add more details such as the information they want to hold about the entities and relationships, which are the attributes and any constraints on the entities, relationships, and attributes. These rectangles are named with the entity set they represent.ĮR modeling is a top-down structure to database design that begins with identifying the important data called entities and relationships in combination with the data that must be characterized in the model. Any object, such as entities, attributes of an entity, sets of relationship, and other attributes of relationship, can be characterized with the help of the ER diagram.Įntities: They are represented using the rectangle-shaped box. # Relationships What is Entity Relationship Diagram (ER-Diagram)?ĮR-Diagram is a pictorial representation of data that describes how data is communicated and related to each other.