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Intro to the Entity-Relationship Modeling Technique

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• Modeling
  • Model: (not fashion !!!)

    Model = a representation of a portion/part of the real world

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  • Fact:

    There can be many models for the same portion of the real world Some model can be better than another model

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• How to construct a model
  • How to construct a model:

    We first identify the part of the reality that we want to represent Examples: A university A company And so on.... A model is then constructed by omitting the unimportant information Example: A university has students We omit these unimportant details from students: What shampoo does a student use How many pair of shirts does a student own And so on In other words: The model will only store the important information Example: The name of the student The courses that a student takes And so on

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• Types of models
  • We can categorize models into 3 (broad) categories:

    High level (data) models: This type of model omits a lot of information (So it stores very little details) This type of model is very abstract in nature Low level (data) models: This type of model omits very little of information (So it stores a lot details) This type of model is very detailed in nature Medium level (data) models: This type of model omits a moderate amount of information (So it stores a moderate amount of details)

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• Models studied in this course
  • In this course, we will study 2 kinds of models:

    The Entity-Relationship model This model is a high-level model that can describe the data need of an organization The Relational model This model is a medium-level model that can describe the data storage (file) structure of the data used by an organization

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• Modeling technique
  • Modeling technique:

    Modeling technique = an methodology (algorithm) used to design a model (= representation)

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• Modeling Methodlogy used in Database Design
  • There are two fundamentally different approaches to database design:

    An "inexact" approach using the Entity-Relationship : The Entity-Relationalship modeling technique The "exact" normalization approach which is based on mathematical functional dependencies between various attributes. The normalization method

  • Right now, we will study the Entity-Relationship technique.

    The normalization technique is the last topic of this course

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• Concepts in the Entity-Relationship (ER) model
  • The ER model is based on two fundamental concepts :

    Entity = a thing in the real world. Entities in the model = a thing that we find very important An entity must be so important that you want to store information about that "thing" !!! Typically, our database model will only represent a small portion of the real world, or a "micro-world". Relationship = is a mathematical concept based on mathematical relations We will discuss relationship later (you may still remember its definition from your calculus days....)