1. An Introduction to Software Engineering Support Lecture

2. Objectives l Introduce software engineering and to explain its importance l Set out the answers to key questions about software engineering

3. FAQs about software engineering l What is software engineering? l What is the difference between software engineering, computer science, and systems engineering? l What is the software crisis? l What are the costs of software engineering? l What is software and what are the attributes of good software? l What is a software process and a software process model? l What are software engineering methods? l What is CASE (Computer-Aided Software Engineering) l What are the key challenges facing software engineering?

4. What is software engineering? “The establishment and use of sound engineering principles in order to obtain economically built software that is reliable and works efficiently on real machines.” “Software Engineering: (1) The application of a systematic, disciplines, quantifiable approach to the development, operation, and maintenance of software; that is the application of engineering to software. (2) The study of approaches as in (1).” l IEEE Definition (1993) l Classic Definition (1969) From Wikipedia l Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software.[1]software[1]

5. 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).

6. What is the difference between software engineering and computer science? COMPUTER SCIENCE CUSTOMER SOFTWARE ENGINEERING Theories Computer Functions Problem Tools and Techniques to Solve Problem

7. What is the difference between software engineering and system engineering? l System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering. Software engineering is part of this process concerned with developing the software infrastructure, control, applications and databases in the system. l System engineers are involved in system specification, architectural design, integration and deployment.

8. What is the study of Software Engineering? Study of the products produced Study of the process used to produce the products. The final products are software components. They may be fully executables components, programs, modules, systems, or simply methods. There are many sotware deliverables between the specification of the products and the actual products. The software development life cycle describes the development process for producing software products. However there are many other items within the process. We will investigate the full process of software engineering.

9. Problems Which Led to the Software Crisis l Increased size and complexity of systems l Cost overruns l Design bugs after implementation l Maintenance ripple effect l Requirements and design needed development tools, not just in the programming tools

10. Software Crisis Today l Research from Standish Group Data on 9236 development projects completed in 2004.

11. Software Crisis Today l 2002 survey of information technology organizations by Cutter Consortium Data 78% have been involved in disputes ending in litigation In 67% of the disputes, the functionality of the information system as delivered did not meet up to the claims of the developers In 56% of the disputes, the promised delivery date slipped several times In 45% of the disputes, the defects were so severe that the information system was unusable

12. Solution to Software Crisis l Use of modern software engineering methodologies l Use of a high-level language that encourages and enforces these principles

13. Software Engineering Definition (revisited) l The software crisis yielded yet another definition of software engineering: l Discipline whose aim is the production of fault-free software, delivered on time and within budget, that satisfies the client’s needs

14. What are the costs of software engineering? l Software costs dominate computer systems costs. Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs. l Software maintenance costs are more than software development costs. For systems with a long life the maintenance may be several times the development costs. And often even bad software has a long life.

15. What are the costs of software engineering? l Costs vary depending on the type of system being developed. The costs depend of the requirements of system attributes such as performance and system reliability as well as the complexity of the type of system being developed. l Distribution of costs depends on the development model that is used.

16. Activity cost distribution

17. Product development costs

18. Maintenance Costs (a) Between 1976 and 1981 (b) Between 1992 and 1998

19. Changing View of Maintenance l Postdelivery maintenance Development-then-maintenance model Temporal definition l Modern maintenance Occurs whenever a fault is fixed or the requirements change, irrespective of whether it takes place before or after installation of the product

21. Why So Costly? l To correct a fault early in the life cycle Usually just a document needs to be changed l To correct a fault late in the life cycle Change the code and the documentation Test the change itself Perform regression testing Reinstall the product on the client’s computer(s)

22. Wear vs. Deterioration

23. The Cost of Change

24. What is Software? Software is a set of items or objects that form a cluster called a configuration. It includes things like: l Number of separate programs l Configuration files which are used to set up these programs l System documentation which describes the structure of the system l Developer and User documentation which explains how to use the system l Data for the system l Web sites for users to download recent product information

25. 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 New software can be created by developing new programs, configuring generic software systems or reusing existing software.

26. What is software? Software products may be l GENERIC developed to be sold to a range of different customers e.g. PC software such as Excel or Word. referred to as commercial off-the-shelf (COTS) software or clickware supplied by a vendor BESPOKE (custom) - developed for a single customer according to their specification. Product specification controlled by the product developer

27. Software Terminology l Open-source software Developed and maintained by a team of volunteers May be downloaded and used free of charge Examples: Linux operating system Firefox web browser Apache web server

28. Software Types o system software o real-time software o business software o engineering/scientific software o embedded software o PC software o AI software o WebApps (Web applications)

29. 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. This means it must be understandable, usable and compatible with other systems.

30. What are the attributes of good software? l From the Users Perspective Correctness Reliability Efficiency Maintainability Usability Robustness l From the Developers Perspective Consistency Understandability Testability Compactness Compatibility Integrity

31. Software Process l A set of activities and associated results which produce a software product l Incorporates a software life-cycle model, techniques, the tools used, and the software developers

32. 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; Component-based software engineering.

33. Software Life-cycle Models l Specifies the various phases of the software process and the order in which they are to be carried out. l Covered in Chapter 1 Dennis

34. What are software engineering methods? l Structured approaches to software development which include system models, notations, rules, design advice and process guidance. l Model descriptions Descriptions of graphical models which should be produced; l Rules Constraints applied to system models; l Recommendations Advice on good design practice; l Process guidance What activities to follow.

35. What is CASE (Computer-Aided Software Engineering) l Software systems that are intended to provide automated support for software process activities. l CASE systems are often used for method support. l Upper-CASE Tools to support the early process activities of requirements and design; l Lower-CASE Tools to support later activities such as programming, debugging and testing.

36. What are the key challenges facing software engineering? l Heterogeneity Developing techniques for building software that can cope with heterogeneous platforms and execution environments; l Delivery Developing techniques that lead to faster delivery of software; Criticality of time to market for commercial products l Trust Developing techniques that demonstrate that software can be trusted by its users. l Shifts in economics of computing Lower hardware costs and greater development and maintenance costs. l Shifts in technology Extensive networking Availability and adoption of OO technology Graphical user interfaces l Budgets and costs l Maintaining Quality

37. Key points l Software engineering is an engineering discipline that is concerned with all aspects of software production. l Software products consist of developed programs and associated documentation. Essential product attributes are maintainability, dependability, efficiency and usability. l The software process consists of activities that are involved in developing software products. Basic activities are software specification, development, validation and evolution. l CASE tools are software systems which are designed to support routine activities in the software process such as editing design diagrams, checking diagram consistency and keeping track of program tests which have been run.