ERD

ERD. Entity Relationship Diagram. Diagram Description automatically generated.

Introduction. White on blue abstract wintry background.

Introduction. Entity-Relationship diagrams or ER diagrams are one of the database design tools that will be useful for you to understand. ER diagrams are pictures that represent how the data in a database are supposed to be connected or related to one another..

How Entity-Relationship Diagrams Work. Top view of cubes connected with black lines.

Representation. Normally, they look like a collection of ovals, rectangles and diamonds collected by lines. Clearly, Diagrams are not fine art. These diagrams can be very helpful for writing tricky queries in database..

Entities. One big red drawing pin in front of many smaller black drawing pins.

Entities. The boxes in the Diagram are called Entities. 01 They represent categories of data your database will keep track of. 02 Each box is one category. 03 Eventually, each entity will probably become a table when the database is made. 04.

Entity Example. Autoradiogram on white paper.

Rules of Entity. Always in Rectangular form. Always be in capital letter. Always Singular..

STUDENT. COLLEGE.

Types of Entity.

Types of Entity. Strong Entity Weak Entity Associative Entity.

Strong Entity. Close-up of chain link.

Strong Entity. These shapes are independent from other entities, and are often called parent entities, since they will often have weak entities that depend on them. They will also have a primary key, distinguishing each occurrence of the entity..

Strong Entity. STUDENT.

Weak Entity.

Weak Entity. Weak entities depend on some other entity type. They don't have primary keys, and have no meaning in the diagram without their parent entity.

Weak Entity. APARTEMENT. WEAK ENTITY.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Weak Entity. BUILDING. APARTEMENT. BuildingID. NumberOfFloors.

Associative entity. Hand with red strings.

Associative Entity. Associative entities relate the instances of several entity types. They also contain attributes specific to the relationship between those entity instances..

Associative Entity. ASSOCIATE ENTITY.

Attributes. Pile of rocks.

Attributes. The ovals in the Diagram are called Attributes. These represent aspects of each category or entity that will be recorded. Attributes will likely become the columns in the table that will be built around that entity. Each attribute in the Diagram has to be connected to at least one entity. Further, according to the rules of set theory, each attribute must be unique for that entity..

STUDENT. COLLEGE. StudentID. StudentName. CollegeStartDate.

Types of Attribute. Colourful rulers and protractors.

Types of Attribute. Simple Attributes Derived Attribute Composite Attribute Multivalued Attribute.

Simple Attributes.

Simple Attributes. Attributes are characteristics of an entity, a many-to-many relationship, or a one-to-one relationship.

Simple Attributes. StudentID.

Derived Attribute. A honeycomb glass surface.

Derived Attribute. Derived attributes are attributes whose value can be calculated from related attribute values..

Derived Attribute. Age. DateOfBirth.

MULTIVALUED ATTRIBUTE. A honeycomb glass surface.

Multivalued Attribute. Multivalued attributes are those that are can take on more than one value..

Multivalued Attribute. Phone Number.

Composite Attribute. A honeycomb glass surface.

Composite Attribute. Important measurement that can be completely reconstructed using other entities..

Composite Attribute. CLASSROOM. ( ClassRoomID ). NumberDesks.

Composite Attribute. CLASSROOM. ( ClassRoomID ). NumberDesk.

Composite Attribute. Building RoomNumber. CLASSROOM.

Multivalued Attribute VS Composite Attribute. A honeycomb glass surface.

Multivalued Attribute VS Composite Attribute. Phone Number.

Multivalued Attribute VS Composite Attribute. Phone Number.

Relationship. A honeycomb glass surface.