notes-shivam

system design

4 min read

  • ANALYSIS AND DESIGN TOOLS
    • [[#ANALYSIS AND DESIGN TOOLS#1. Entity-Relationship Diagram (ERD)|1. Entity-Relationship Diagram (ERD)]]
    • [[#ANALYSIS AND DESIGN TOOLS#2. Decision Tree|2. Decision Tree]]
      • [[#2. Decision Tree#Decision Table|Decision Table]]
    • [[#ANALYSIS AND DESIGN TOOLS#3. Data Flow Diagram (DFD)|3. Data Flow Diagram (DFD)]]
    • [[#ANALYSIS AND DESIGN TOOLS#4. Data Dictionary|4. Data Dictionary]]
      • [[#4. Data Dictionary#Elements of Data Dictionary:|Elements of Data Dictionary:]]
      • [[#4. Data Dictionary#Advantages:|Advantages:]]
    • [[#ANALYSIS AND DESIGN TOOLS#5. Pseudo Code|5. Pseudo Code]]
    • [[#ANALYSIS AND DESIGN TOOLS#6. Input and Output Design|6. Input and Output Design]]
  • STRUCTURED SYSTEM DESIGN
    • [[#STRUCTURED SYSTEM DESIGN#1. Modules|1. Modules]]
    • [[#STRUCTURED SYSTEM DESIGN#2. Structured Chart|2. Structured Chart]]
    • [[#STRUCTURED SYSTEM DESIGN#3. Qualities of Good Design|3. Qualities of Good Design]]
    • [[#STRUCTURED SYSTEM DESIGN#4. Coupling|4. Coupling]]
      • [[#4. Coupling#Types of Coupling:|Types of Coupling:]]
    • [[#STRUCTURED SYSTEM DESIGN#5. Cohesion|5. Cohesion]]
      • [[#5. Cohesion#Types of Cohesion:|Types of Cohesion:]]
    • [[#STRUCTURED SYSTEM DESIGN#6. Case Studies|6. Case Studies]]

ANALYSIS AND DESIGN TOOLS

1. Entity-Relationship Diagram (ERD)

  • Definition: Visual representation of entities in a system and the relationships between them.

  • Components:

    • Entities: Represented by rectangles (e.g., Student, Course).
    • Attributes: Represented by ovals (e.g., Student Name, Course Code).
    • Relationships: Represented by diamonds, linking entities (e.g., Enrollment links Student to Course).

  • Example:
    An ERD for a university system might show a “Student” entity connected to a “Course” entity through an “Enrolled In” relationship.

2. Decision Tree

  • Definition: A tree-like model that represents decisions, their possible outcomes, and associated consequences.
  • Usage: Helps in logical decision-making.
  • Example:
    A decision tree for determining whether to grant a loan might branch based on conditions like “Credit Score” and “Income”.

Decision Table

  • Definition: A tabular representation of conditions and their corresponding actions.

  • Components:

    • Conditions: Columns for decision variables.
    • Actions: Rows for actions to be taken.

  • Example:

    ConditionsHigh CreditLow CreditHigh IncomeLow Income
    Action (Loan)ApproveRejectApproveReject

3. Data Flow Diagram (DFD)

  • Definition: Shows the flow of data within a system, emphasizing inputs, processes, and outputs.

  • Components:

    • External Entity: Represented by rectangles.
    • Process: Represented by circles.
    • Data Store: Represented by open rectangles.
    • Data Flow: Represented by arrows.

  • Example:
    For an online ordering system:

    • External Entity: Customer
    • Process: Place Order
    • Data Store: Orders Database
    • Data Flow: Customer → Place Order → Orders Database

4. Data Dictionary

  • Definition: A centralized repository of information about data elements, their meaning, relationships, and usage.

Elements of Data Dictionary:

  • Data element name
  • Description
  • Data type (e.g., integer, string)
  • Size (e.g., 10 characters)
  • Allowed values or range

Advantages:

  • Simplifies communication between team members.
  • Helps maintain data consistency.
  • Facilitates system design and documentation.

5. Pseudo Code

  • Definition: A plain-English representation of program logic, focusing on structure rather than syntax.

  • Example:

    IF age >= 18 THEN  
    PRINT "Eligible to vote"  
ELSE  
    PRINT "Not eligible to vote"

6. Input and Output Design

  • Input Design: Focuses on how data is captured (e.g., forms, input fields).
    • Goals: Reduce errors, ensure clarity.
    • Example: A login form with fields for username and password.
  • Output Design: Deals with how information is presented (e.g., reports, dashboards).
    • Goals: Ensure readability and usability.
    • Example: An invoice generated after a purchase.

STRUCTURED SYSTEM DESIGN

1. Modules

  • Concept: A system is divided into smaller, manageable units (modules).
  • Types of Modules:
    1. Control Module: Coordinates other modules.
    2. Functional Module: Performs a specific task.

2. Structured Chart

  • Definition: A hierarchical diagram showing system modules and their relationships.
  • Example: A payroll system may have modules like Employee Data, Tax Calculation, and Pay Generation.

3. Qualities of Good Design

  • Modularity: Breaks system into independent parts.
  • Scalability: Accommodates future growth.
  • Readability: Easy for developers to understand.
  • Flexibility: Allows changes without major redesign.

4. Coupling

  • Definition: The degree of dependency between modules.

Types of Coupling:

  1. Content Coupling: One module uses another’s data directly.
  2. Control Coupling: One module controls the behavior of another.
  3. Data Coupling: Modules communicate through well-defined data.
  4. Low Coupling: Ideal; reduces dependencies.

5. Cohesion

  • Definition: The degree to which elements in a module belong together.

Types of Cohesion:

  1. Functional Cohesion: Performs a single, well-defined task.
  2. Sequential Cohesion: Output of one part is input to another.
  3. Logical Cohesion: Performs related tasks.

6. Case Studies

  • Example: Hospital Management System
    • Modules: Patient Records, Billing, Appointment Scheduling.
    • Input Design: Patient details form.
    • Output Design: Bills, patient reports.
    • ERD: Shows relationships like Patient → Doctor → Treatment.

Let me know if you’d like diagrams for any section!

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