DBMS Relationships

DBMS Relationships are a fundamental & core principal which is used to make objects behave with each other. We use DBMS Relationships to define how entities in DBMS relates to each other and to what extent they will communicate with each other.
Recently , we talked about  ERD Terminologies and discussed about entities and attributes in detailed. In case , you haven’t read the article it is a must read . Some wonderful details for you to go through.
It is time we discuss about how different entities in a design interacts together . Before we dive into it  , you should know one very important thing about DBMS .  When we design a DBMS , we are practically translating real life into it and perhaps this is why this field is one of the most practical in Computer Sciences.  Due to this sole reason , designing a DBMS is just like your real world and how things ( objects )  interact out there is how they will interact here.

DBMS Relationships

People interact with each other when they have a relationship/acquaintances between them . Our DBMS entities do the same . Two entities communicate with each other by a relationship

We will discuss about

  1. DBMS Relationships
  2. Degrees of Relationships


Behaviour or association between relation is called a relationship.This is represented by the following symbol

            ERD Terminologies relationship is represented as below.


Number of entities that share a relationship is called the degree of relationships . We have basically three type of degrees .

 Unary Relationship :

                          When entity has a relationship with itself , that’s a unary relationship.  Self-Joins are the perfect example.  Usually when entity has a parent-child relationship in its columns , then this happens.

Unary Relation Example could be that you need to pass certain subjects to take others as they are pre-requisites of them . Presentation will be :

Binary Relationship :

When two entities share a relationship in database management system with each other that is called a binary relationship . Example could be Teacher teaches a Subject. Two entities one relationship.

Ternary Relationship :

When three entities share a relationship with each other . Example could be a Students taking Subjects from Teachers.
Using the diagram of our  ERD Terminologies . Here Student , Teacher and Subject has a ternary relationship.  

You can see a design DBMS in making and we have created relationships among entities using relationships .
So far I have deliberately , kept you away from a lot of technical definitions . Remember , the idea is to explain in human language and we have made great progress so far . In my next article , we will discuss the cardinality of entities with each other considering their relation and then we’ll move towards essence of DBMS. Stay Tuned!
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