Articles

Entity Relationship Diagram (ERD) — Part-II

In Database Systems on June 16, 2012 by Muhammad Haadi Tagged: , , , , , , , , ,

Cardinality of a Relationship

Cardinality is the mapping of entities i-e zero, one or many. It basically explains how a table is linked to another table. It can be particularized more as the number of distinct values of a table connected to how many values of the other table – both minimum and maximum.

NOTE: Some authors explain optionality as a separate concept which is zero or one in this case.

Following are the two possible classifications of relations among entities.

  • One to One
  • One to Many

There is also a third case of (Many to Many) relationship but I consider it separate from the two basic classifications as it is basically resolved with the help of the same technique used in resolving (one to many) relationship. We will see that in detail later.

We will first discuss the One-to-Many and Many-to-Many  scenario as the example I am going to use is the One-to-One relation would need an understanding of one-to-many relation.

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Articles

Post Entity Relationship Diagram (ERD) – Part-I

In Database Systems on January 13, 2012 by Muhammad Haadi Tagged: , , , , , , ,

This topic has always been a challenge for me to discuss. It’s not that elaborating the concept among a bunch of students bothers me but the thing is that normally students get confused in the twists and turns this topic has.

However, I am going to keep things simple by using the divide and conquer approach, i-e. I will segregate the two main portions involved in this topic

  • the basics of ERD and
  • the one with relations explained

Therefore, that would make the concepts quite easy to understand and learn.

Note:There are various explanations of these concepts over the internet as some authors keep different concepts isolated to make them more understandable while others try not to indulge a newbie into the details. So, if you feel difficulty anywhere, feel free to ask. Read More »

Articles

The Evolution of Database

In Database Systems on October 18, 2010 by Muhammad Haadi

From pre-stage flat-file system, to relational and object-relational systems, database technology has gone through several generations and its history that is spread over more than 40 years now.

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Articles

Databases, an Introduction

In Database Systems on August 27, 2010 by Muhammad Haadi

Welcome to the exciting world of database development! In this series of articles, I will introduce you to databases and help you knowing how to effectively use them.

According to my opinion, if you are reading this article, you must have the basic know how of a file system and you must have heard of databases. Read More »

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