Understanding Software Engineering Principles

The Definition of Software Engineering A discipline that requires the knowledge of mathematical and natural sciences gained by study, experience and practice is applied to the systematic development of correct, consistent and maintainable software products. 6/24/2025 Lecture 1 1

The Nature of Software Software is intangible Software is easy to reproduce Cost is in its development in other engineering products, manufacturing is the costly stage The industry is labor-intensive Hard to automate 6/24/2025 Lecture 1 2

The Nature of Software Much software has poor design and is getting worse Demand for software is high and rising We are in a perpetual software crisis We have to learn to engineer software 6/24/2025 Lecture 1 3

What is Software Engineering? The process of solving customers problems by the systematic development and evolution of large, high-quality software systems within cost, time and other constraints Other definitions: IEEE: (1) the application of a systematic, disciplined, quantifiable approach to the development, operation, maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1). 6/24/2025 Lecture 1 4

What is Software Engineering? Solving customers problems This is the goal of software engineering Sometimes the solution is to buy, not build Adding unnecessary features does not help solve the problem Software engineers must communicate effectively to identify and understand the problem 6/24/2025 Lecture 1 5

What is Software Engineering? Systematic development and evolution An engineering process involves applying well understood techniques in a organized and disciplined way Many well-accepted practices have been formally standardized e.g. by the IEEE or ISO Most development work is evolution 6/24/2025 Lecture 1 6

What is Software Engineering? Large, high quality software systems Software engineering techniques are needed because large systems cannot be completely understood by one person Teamwork and co-ordination are required Key challenge: Dividing up the work and ensuring that the parts of the system work properly together The end-product must be of sufficient quality 6/24/2025 Lecture 1 7

What is Software Engineering? Cost, time and other constraints Finite resources The benefit must outweigh the cost Others are competing to do the job cheaper and faster Inaccurate estimates of cost and time have caused many project failures 6/24/2025 Lecture 1 8

Software Engineering Software engineering as a discipline is focused on To significantly increase software productivity (P) and software quality (Q) while reducing software costs (C) and time to market (T) software PQCT 6/24/2025 Lecture 1 9

Types of Software Custom Generic For a specific customer Sold on open market Often called COTS (Commercial Off The Shelf) Shrink-wrapped Embedded Built into hardware Hard to change 6/24/2025 Lecture 1 10

Types of Software Real time software Example: control and monitoring systems Must react immediately Safety often a concern Data processing software Used to run businesses Accuracy and security of data are key Some software has both aspects 6/24/2025 Lecture 1 11

Challenges posed by Software How do we ensure quality ? How do we define quality ? How do we measure quality ? Will a quality defined for one software product be applied to another software product? We can do that for hardware products if one product is a component of another Does the definition of a particular quality remain the same forever? 6/24/2025 Lecture 1 12

Challenges posed by Software (continued) How do we cope with aging software? often encounter the situation that a software product becomes old and needs replacement The rate of aging does not seem to be predictable a payroll application written in COBOL used in IBM mainframe for 17 years, but the next payroll application written in Pascal/C running on DEC VMS last for only 8 years 6/24/2025 Lecture 1 13

Challenges posed by Software (continued) How often we need to upgrade software? Windows 95 was replaced by Windows 98 and was then replaced by Windows Millennium, Windows XP, now Windows Vista, Windows 7 Will the application programs/data written in the previous version still be usable in the next version? What are the chances of failures? What about the cost of upgrades? 6/24/2025 Lecture 1 14

Challenges posed by Software (continued) How to develop software on or before the deadline? until 1999, more than 80% of software projects were finished only AFTER the deadline in many cases, software development projects went beyond the deadline limits that the customers cancelled the projects what need to be done to meet the deadline? 6/24/2025 Lecture 1 15

Goals of Software Engineering Education To develop correct, consistent and maintainable software products To meet deadlines while developing software products To make software development processes well- documented and easily accessible so that newcomers to a software development project can join and continue without much difficulties (must reduce training overhead) To make software development processes visible to a hierarchy of people involved in the development process 6/24/2025 Lecture 1 16

Software Engineering and the Engineering Profession The term Software Engineering was coined in 1968 People began to realize that the principles of engineering should be applied to software development Engineering is a licensed profession In order to protect the public Engineers design artifacts following well accepted practices which involve the application of science, mathematics and economics Ethical practice is also a key tenet of the profession In many countries, much software engineering does not require an engineering license, but is still engineering 6/24/2025 Lecture 1 17

Software Engineering and Computer Science Computer Science Pursue optimal solutions $$$ is not an important consideration Programming in the small Technical issues Dealing with tame problems Software Engineering Good enough is enough $$$ is an important factor (PQCT) Programming in the large All issues and aspects Dealing with wicked problems Building on top of computer science and other disciplines Foundations of software engineering 18

Software Engineering and the Engineering Profession Ethics in Software Engineering: Software engineers shall Act consistently with public interest Act in the best interests of their clients Develop and maintain with the highest standards possible Maintain integrity and independence Promote an ethical approach in management Advance the integrity and reputation of the profession Be fair and supportive to colleagues Participate in lifelong learning 6/24/2025 Lecture 1 19

Stakeholders in Software Engineering Users Those who use the software Customers Those who pay for the software Software developers Development Managers All four roles can be fulfilled by the same person 6/24/2025 Lecture 1 20

Software Quality Usability Efficiency It doesn t waste resources such as CPU time and memory Reliability It does what it is required to do without failing Maintainability It can be easily changed Reusability Its parts can be used in other projects, so reprogramming is not needed Users can learn it and fast and get their job done easily 6/24/2025 Lecture 1 21

Software Quality and the Stakeholders Customer: solves problems at an acceptable cost in terms of money paid and resources used User: easy to learn; efficient to use; helps get work done QUALITY SOFTWARE Development manager: sells more and pleases customers while costing less to develop and maintain Developer: easy to design; easy to maintain; easy to reuse its parts 6/24/2025 Lecture 1 22

Software Quality: Conflicts and Objectives The different qualities can conflict Increasing efficiency can reduce maintainability or reusability Increasing usability can reduce efficiency Setting objectives for quality is a key engineering activity You then design to meet the objectives Avoids over-engineering which wastes money Optimizing is also sometimes necessary Example: obtain the highest possible reliability using a fixed budget 6/24/2025 Lecture 1 23

The 4P Model Software Engineering involves Product Process Process People Product People Project Project 6/24/2025 Lecture 1 24

Software Engineering Projects Most projects are evolutionary or maintenance projects, involving work on legacy systems Corrective projects: fixing defects Adaptive projects: changing the system in response to changes in Operating system Database Rules and regulations Enhancement projects: adding new features for users Reengineering or perfective projects: changing the system internally so it is more maintainable 6/24/2025 Lecture 1 25

Software Engineering Projects Green field projects New development The minority of projects 6/24/2025 Lecture 1 26

Software Engineering Projects Projects that involve building on a framework or a set of existing components A framework is an application that is missing some important details Example: Specific rules of this organization Such projects: Involve plugging together components that are: Already developed. Provide significant functionality Benefit from reusing reliable software Provide much of the same freedom to innovate found in green field development 6/24/2025 Lecture 1 27

Activities Common to Software Projects Requirements and specification Domain analysis Defining the problem Requirements gathering Obtaining input from as many sources as possible Requirements analysis Organizing the information Requirements specification Writing detailed instructions about how the software should behave 6/24/2025 Lecture 1 28

Activities Common to Software Projects Design Deciding how the requirements should be implemented, using the available technology Systems engineering: Deciding what should be in hardware and what in software Software architecture: Dividing the system into subsystems and deciding how the subsystems will interact Detailed design of the internals of a subsystem User interface design Design of databases 6/24/2025 Lecture 1 29

Activities Common to Software Projects Modeling Creating representations of the domain or the software Use case modeling Structural modeling Dynamic and behavioral modeling Implementation Quality Assurance Reviews and inspections Testing Maintenance 6/24/2025 Lecture 1 30

A Software Engineering Process Identify Corporate practices Plan Plan Quality Assurance Configuration Management Plan verification and validation methods Plan development process Analyze Requirements Design Implement Test Maintain 6/24/2025 Lecture 1 31

Software Engineering Process Software Engineering 70 60 50 40 Without SE Applying SE Effort 30 20 10 0 Design Testing Analysis Specification Implementation Software Life Cycle Phase 6/24/2025 Lecture 1 32

Standards and Practices Provide a disciplined approach to software development process Standards IEEE, ISO, ANSI, Practices CMM, Rational, 6/24/2025 Lecture 1 33

Capability Maturity Model (CMM) Developed by Software Engineering Institute (SEI) at Carnegie-Mellon in 1980s Department of Defense wanted to establish the standards for software development organizations in order to restrict bidding for government contracts Result: organizations have to be certified as CMM-Level (?) for bidding government contracts 6/24/2025 Lecture 1 34

CMM Continuously improving process Level 5 Optimizing Predictable process Level 4 Managed Standard, Consistent process Level 3 Defined Disciplined Process Repeatable Level 2 Initial Level 1 6/24/2025 Lecture 1 35

CMM Level 1: Initial ad hoc processes; no formalized method for any activity no project plans success depends on efforts of individuals in the organization software development process continuously changes 6/24/2025 Lecture 1 36

CMM Level 2: basic project management established project plan incorporated; estimates are realistic and based on previous projects purpose: to track cost, schedule and functionalities process improvement occurs based on the success of previous projects (that is why the level is called repeatable ) Repeatable 6/24/2025 Lecture 1 37

CMM Level 3: processes are documented, standardized and integrated with other processes project management refined from previous level every process (activity) is verified; subject to the standards established; modifications and new processes are documented in short, an iterated version of level 2 Defined 6/24/2025 Lecture 1 38

CMM Level 4: both process management and product management incorporated quantitative analysis of processes and products conducted; measurement procedures for quantitative analysis are established in short, quality assurance of products is given more importance at this level Managed 6/24/2025 Lecture 1 39

CMM Level 5: introduces research-oriented processes to continuously improve (to optimize) the existing processes and policies best software engineering processes and management practices are used throughout the organization Optimizing 6/24/2025 Lecture 1 40

Exercise Software Engineering Institute (SEI) at Carnegie Mellon University developed Capability Mature Model Integration (CMMI) in 2007. Find out the differences between CMM and CMMI. 6/24/2025 Lecture 1 41