To help you to design database diagrams by identifying entities, their attributes, relationships and cardinalities.
What is ER Model (Entity Relationship Model):
ER Model (Entity Relationship Model) is a high-level conceptual data model diagram. ER model
helps to systematically analyze data requirements to produce a well-designed database. The ER
Model represents real-world entities and the relationships between them. Creating an ER Model
in DBMS is considered as a best practice before implementing your database.
Entity Relationship Diagram Symbols & Notations:
Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which
are rectangle, oval and diamond to represent relationships between elements, entities and
attributes. All other sub-elements are based on main elements in ERD Diagram. Following are the
main components and its symbols in ER Diagrams:
- • Rectangles: This Entity Relationship Diagram symbol represents entity types
- • Ellipses : Symbol represent attributes
- • Diamonds: This symbol represents relationship types
- • Lines: It links attributes to entity types and entity types with other relationship types
- • Primary key: attributes are underlined
- • Double Ellipses: Represent multi-valued attribute.
Components of the ER Diagram:
Components of the ER Diagram: This model is based on four basic concepts:
1. Entities - An entity is an object in the real world that is distinguishable from other objects
2. Attributes - An entity is described using a set of attributes whose values are used to
distinguish one entity from another of same type.
3. Relationships - A relationship is an association among several entities
4. Cardinality - Express the number of entities to which another entity can be associated via
a relationship set. For a binary
relationship set, the mapping
cardinality must be one of the
following types:
• One-to-one
• One-to-many
• Many-to-one
• Many-to-many
How to draw ERD:
Lets see how we can draw ERD-Diagram.
1. Identify Entities by finding nouns (person, place event, object or concept)
2. Identify entity attributes/features
3. Identify relationships between entities (Relationship name is an active or a passive verb)
4. Define cardinalities
5. Draw ERD
Practice Problem
Task is from Wally Los Gatos problem.
The ERD-Diagram is shown below.
Steps are already explained to you .
Task Develop an E-R diagram for Mountain View Community Hospital. State any assumptions you
made in developing the diagram.
The E-R Diagram is as:
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