Lecture 5 - Entity Relationship Diagram



ERD is a way of representing database relations in a graphical form. As you know that the entities are represented using rectangle and attributes using ovals.

Let’s revisit the relationship of a teacher and student. As you can see that one teacher teaches many students.

First Relation


 

Second Relation


Similarly, many subjects are studied by many students.



Merge Relations

 

 

 Now! You must be thinking what is the relationship of teacher and subject? Probably your answer is many-to-many . . .

I would rather disagree with your point of view; the reason will be discussed with you when we would implement this ERD in a DBMS. The completed ERD would be

Finalized Relations




That was simple ERD; it cannot be implemented in any DBMS. What else is required? What is missing? Do you remember the term ‘attribute’? Yes the answer is ‘attributes’ which are not defined.

Let’s define some attributes


Now there should be some relationship among these entities. The assignment is yours . . .
Location: Siālkot, Pakistan

Comments

Post a Comment

Popular posts from this blog

Lecture 17 – Functions (continued)

Let’s see how we can write a function which takes no argument but returns a value. Type 2 – Functions that take NO argument and returns A value I would write a function which would 1.        Ask the user to input a number 2.        Calculate its square 3.        Return the calculated value to main function 4.        Main function will display calculated result   #include <stdio.h> #include <conio.h>   void square() { int number; printf(“\nPlease enter a number :”); Output There would be no output as it has a syntax error. The error is LVALUE REQUIRED scanf(“%d”, &number); number = number * number; return number; } void main() { clrscr();         ...
Read more

Lecture 6 – Operators in C (continued)

1.      Binary Arithmetic Operators                                                               i.       Addition   +                                                             ii.       Subtraction   -                 ...
Read more

Lecture 10 – Decisions (if-else-if)

if-else-if Consider a scenario where we have to check multiple conditions which are related to each other. For example we enter marks of a student and then we assign a grade to it. Marks Grade >=80 A >=70 and <80 B >=60 and <70 C >=50 and <60 D <50 Fail   In above scenario, if we use simple if then we need to use FIVE if statements. These if’s would be checked every time, even if the first condition is true. Syntax if(condition) { // Statements if true } else if (condition) { //Statements if true } else if (condition) { //Statements if true } else if (condition) { //Statements if true } else if (condition) { //Statements if true } . . else { }   With à if Example 19 - Grading system using if With à if-else-if Exam...
Read more