Software Engineering - Lecture Slides | CMSC 435, Exams of Software Engineering

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CMSC 435: Software Engineering

Course overview

Topics covered today

l Course requirements l FAQs about software engineering l Professional and ethical responsibility

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Course Objectives

l To introduce software engineering and to explain its importance in building large programs

l To understand the process of developing new technology and the role of experimentation

l To set out the answers to key questions about software engineering

l To introduce ethical and professional issues and to explain why they are of concern to software engineers

CMSC 435 requirements

l Exam 1 (20%) and Exam 2 (20%) l Project (40%) l Report (10%) l Other (homework, presentations, …) (10%) l Project goal is to take a large system and add several features to it:
System is a prototype of an FAA air traffic control system called TSAFE.
You have to make decisions on the implementation and test your results
Projects are group activities; system written in Java.
For EACH phase of the project you will be in a different group, randomly assigned l Use class website. (www.cs.umd.edu/~mvz/cmsc435-s09/)

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Aspects of software engineering

l Analysis vs. synthesis of a problem

l Method or technique: procedure for producing a result

l Tool: instrument or automated system for accomplishing something

l Procedure: recipe for combination of tools and techniques

l Paradigm: style of doing something

Two aspect of Software Engineering:

Analysis

PROBLEM

Subproblem 1 Subproblem 2 (^) Subproblem 3Subproblem 4

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Two aspect of Software Engineering:

Synthesis

SOLUTION

Solution 1 Solution 2 (^) Solution 3 Solution^4

Software costs

l Software costs often dominate computer system costs. The costs of software on a PC are always greater than the hardware cost.

l Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs.

l Software engineering is concerned with cost- effective software development.

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FAQs about software engineering

l What are the costs of software engineering? l What are software engineering methods? l What is CASE (Computer-Aided Software Engineering) l What are the attributes of good software? l What are the key challenges facing software engineering?

What is software?

l Computer programs and associated documentation such as requirements, design models and user manuals. l Software products may be developed for a particular customer or may be developed for a general market. l Software products may be
Generic - developed to be sold to a range of different customers e.g. PC software such as Excel or Word.
Custom - developed for a single customer according to their specification. l New software can be created by developing new programs, configuring generic software systems or reusing existing software. (Reuse is emphasis this semester)

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What is software engineering?

l Software engineering is an engineering discipline that is concerned with all aspects of software production. l Software engineers should adopt a systematic and organised approach to their work and use appropriate tools and techniques depending on the problem to be solved, the development constraints and the resources available.

What is the difference between software

engineering and computer science?

l Computer science is concerned with theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software. l Computer science theories are still insufficient to act as a complete underpinning for software engineering (unlike e.g. physics and electrical engineering).

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Typical development processes

. Requirements engineering

• System analysis
• High-level design/architecture
• Low-level design
• Coding
• Integration
• Design and code reviews
• Testing
• Maintenance
• Project management
• Configuration management

What is a software process model?

l A simplified representation of a software process, presented from a specific perspective.

l Examples of process perspectives are
Workflow perspective - sequence of activities;
Data-flow perspective - information flow;
Role/action perspective - who does what. l Generic process models
Waterfall;
Iterative development;
Agile development;
Component-based software engineering.

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What are the costs of software

engineering?

l Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs.

l Costs vary depending on the type of system being developed and the requirements of system attributes such as performance and system reliability.

l Distribution of costs depends on the development model that is used.

Activity cost distribution

Product development

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What are the attributes of good software?

l The software should deliver the required functionality and performance to the user and should be maintainable, dependable and acceptable. l Maintainability
Software must evolve to meet changing needs; l Dependability
Software must be trustworthy; l Efficiency
Software should not make wasteful use of system resources; l Acceptability
Software must accepted by the users for which it was designed; it must be understandable, usable and compatible with other systems.

What are the key challenges facing

software engineering?

l Heterogeneity, delivery and trust. l Heterogeneity
Developing techniques for building software that can cope with heterogeneous platforms and execution environments; l Delivery
Developing techniques that lead to faster cost- effective delivery of software; l Trust
Developing techniques that demonstrate that software can be trusted by its users.

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Programming

Specification

Design

Code

Test

Programming Software Engineering

Specification

Design

Code

Test

1. Use of correct tools

• • Use casesModel checking for each process
• OO Design
• Inspections
• Cleanroom
• Agile
• Black and whitebox testing
• Capture/recapture
• Regression testing

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Programming Systems extend to entire life

cycle of product

l Problem: Program to read in a rational number and compute its square root. l Programming solution: A relatively small program in some programming language. l Programming system:

• Source program in some language
• Executable file for common platforms
• Installation script to install on various platforms
• Documentation of requirements
• Documentation of design
• Error messages and corrective action
• Timing and performance data
• Users guide
• Test data
• Help system to fix errors Turn in this programming system on Thursday, February 5th

Professional and ethical responsibility

l Software engineering involves wider responsibilities than simply the application of technical skills. l Software engineers must behave in an honest and ethically responsible way if they are to be respected as professionals. l Ethical behavior is more than simply upholding the law.

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Issues of professional responsibility

l Confidentiality
Engineers should normally respect the confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed. l Competence
Engineers should not misrepresent their level of competence. They should not knowingly accept work which is beyond their competence.
Issue: Should software engineers be licensed? What does competence really mean here?

Issues of professional responsibility

l Intellectual property rights
Engineers should be aware of local laws governing the use of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected. l Computer misuse
Software engineers should not use their technical skills to misuse other people’s computers. Computer misuse ranges from relatively trivial (game playing on an employer’s machine, say) to extremely serious (dissemination of viruses).

Key points

l Computer science is concerned with getting the computer to do what you want it to do, as efficiently as possible. l Software engineers use their computer science skills to create products of practical use and economic value. Software engineers are ethically responsible for the correctness, suitability, and safety of their projects. When possible, software engineers apply scientific and mathematical knowledge to their work. l A software development process is a process by which user needs are translated into a software product. Software development processes are comprised of specific software development practices. l A software process model is a generalized abstraction of a family of software development processes. l Plan-driven processes are best for projects with a low degree of change or those with critical safety and security needs. l Software engineering is especially challenging because software is a tractable medium, requirements often change, and competitive pressures cause schedule pressure.