DBMS Relationships

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.

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. Relationships
  2. Degrees of Relationships

RELATIONSHIP :

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

            ERD Terminologies relationship is represented as below.

weakrelationship

DEGREES OF RELATIONSHIPS :

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.

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

      Binary Relationship :

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

binaryrelationship

      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.  ternary

 

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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