Understanding Abstraction, Decomposition, and Hierarchy in Software Systems, Slides of Database Management Systems (DBMS)

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Object Oriented Software EngineeringUsing UML, Patterns, and Java

Chapter 2,

Modeling with UML,

Part 1

Odds and Ends (2)

• (^) Reading for this Week:
  • (^) Chapter 1 and 2, Bruegge&Dutoit, Object-Oriented Software Engineering
• (^) Software Engineering I Portal
• (^) Lectures Slides:
  • (^) Will be posted after each lecture.

What is the problem with this

Drawing?

Abstraction

• (^) Complex systems are hard to understand
  • (^) The 7 +- 2 phenomena
    • (^) Our short term memory cannot store more than 7+- pieces at the same time -> limitation of the brain
    • (^) TUM Phone Number: 498928918204

Abstraction

TUM Phone Number

StateCode CityCode^ TUMcode^ OfficePart

• (^) Chunking:
  • (^) Group collection of objects to reduce complexity
  • (^) State-code, city-code, TUM-code, Office-Part
• (^) Complex systems are hard to understand
• (^) The 7 +- 2 phenomena
• (^) Our short term memory cannot store more than 7+- pieces at the same time -> limitation of the brain
• (^) TUM Phone Number: 498928918204

Abstraction

• (^) Abstraction allows us to ignore unessential details
• (^) Two definitions for abstraction:
  • (^) Abstraction is a thought process where ideas are distanced from objects - (^) Abstraction as activity
  • (^) Abstraction is the resulting idea of a thought process where an idea has been distanced from an object - (^) Abstraction as entity
• (^) Ideas can be expressed by models

We use Models to describe Software Systems

• (^) Object model: What is the structure of

the system?

• (^) Functional model: What are the

functions of the system?

• (^) Dynamic model: How does the system

react to external events?

• (^) System Model: Object model +

functional model + dynamic model

Other models used to describe Software System Development

• (^) Task Model:
  • (^) PERT Chart: What are the dependencies between tasks?
  • (^) Schedule: How can this be done within the time limit?
  • (^) Organization Chart: What are the roles in the project?
• (^) Issues Model:
  • (^) What are the open and closed issues?
    • (^) What blocks me from continuing?
  • (^) What constraints were imposed by the client?
  • (^) What resolutions were made?
    • (^) These lead to action items

Issue-Modeling Issue: What is the Center of the Universe? Proposal1: The earth! Proposal2: The sun! Pro: Copernicus says so. Pro: Aristotle says so. Pro: Change will disturb the people. Con: Jupiter’s moons rotate around Jupiter, not around Earth. Resolution (1615): The church decides proposal 1 is right

Issue-Modeling Issue: What is the Center of the Universe? Proposal1: The earth! Proposal2: The sun! Pro: Copernicus says so. Pro: Aristotle says so. Pro: Change will disturb the people. Con: Jupiter’s moons rotate around Jupiter, not around Earth. Resolution (1615): The church decides proposal 1 is right Resolution (1998): The church declares proposal 1 was wrong Proposal3: Neither! Pro: Galaxies are moving away From each other.

Decomposition (cont’d)

• (^) Object-oriented decomposition
  • (^) The system is decomposed into classes (“objects”)
  • (^) Each class is a major entity in the application domain
  • (^) Classes can be decomposed into smaller classes
• (^) Object-oriented vs. functional decomposition Which decomposition is the right one?

Functional Decomposition

Top Level functions Level 1 functions Level 2 functions Machine instructions System Function Load R10 Add R1, R Read Input Transform^ Produce Output Transform Produce Output Read Input

Functional Decomposition

• (^) The functionality is spread all over the system
• (^) Maintainer must understand the whole system to

make a single change to the system

• (^) Consequence:
  • (^) Source code is hard to understand
  • (^) Source code is complex and impossible to maintain
  • (^) User interface is often awkward and non-intuitive
• (^) Example: Microsoft Powerpoint’s Autoshapes
• (^) How do I change a square into a circle? ?

Changing a Square into a Circle