ER Diagram

Question 1

What is an ER Diagram?

Answer 1

ER Diagram is a graphical approach to database design.

It uses Entity/Relationship to represent real-world objects.

Represents conceptual database as viewed by end-user.

Question 2

💗Entity?
💗Attributes?
💗Domain?
💗Composite Attribute?
💗Multivalued Attribute?
💗Derived Attribute?
💗Key Attribute?
💗Primary Key?
💗Composite Key?
💗Super Key?
💗Relationship?
💗Degree of Relationship?
💗Total Participation and Partial Participation?
💗Descriptive Attributes?
💗Weak Entity?
💗Foreign Key?

Answer 2

💗 Entity - is an object in the real world with an independent existence.
💗Attributes - are used to describe entities. (properties or characteristics)
💗Domain - is the set of allowable values for an attribute.
E.g.: Domain of “gender” would include the values ‘Male’ and ‘Female’.
💗Composite Attribute - can be divided into smaller parts.
💗Multivalued Attribute - contains multiple values.
💗Derived Attribute - can be derived.
💗Key Attribute - Minimal set of attributes that uniquely identify
an entity in the entity list.
💗Primary Key - Attribute that uniquely identifies the entity.
💗Composite Key - A key that has more than one attribute.
💗Super Key - Any other set of attributes that uniquely identify
an entity.
E.g: (SID+Name) Is this unique? Yes, but not the minimal set.
Referred to as Super Key.
💗Relationship - is an association of entities showing how the
entities are related to each other.
💗Degree of Relationship - No of participating entities in a relationship.
E.g: Binary - relationship with 2 participants. Degree = 2,
Ternary - Degree = 3, Quaternary - Degree = 4

💗Total Participation − Each entity is involved in the relationship. Total participation is represented by double lines. Partial participation − Not all entities are involved in the relationship. Partial participation is represented by single lines.

💗Descriptive Attributes - Used to record information about
the relationship.
💗Weak Entity - entities that can’t exist on its own. (don’t have
any key attribute)
– The attributes in the weak entity participating in the key
are called partial keys.
– The owner entity and the weak entity participate in an
identifying relationship.
– The weak entity must have total participation in the
identifying relationship.

💗Foreign Key - Attribute in a table that serves as a reference to the primary key of another table.