Course Notes Set 1: Introduction to Software Engineering

1. Course Notes Set 1:Introduction toSoftware Engineering Computer Science and Software Engineering Auburn University

2. Desirable Attributes of Software • Maintainability • It should be possible to evolve software to meet the changing needs of customers. • Dependability • Software dependability includes a variety of things such as reliability, security and safety. Dependable software should not cause physical or economic damage in the event of a system failure.

3. Desirable Attributes of Software • Efficiency • Software should not waste system resources such as memory and processor cycles. • Usability • Software should have an appropriate user interface and adequate documentation. • Etc., etc. Achieving these qualities in software is hard to do!

4. No Silver Bullet But as we look to the horizon of a decade hence, we see no silver bullet. There is no single development, either in technology or management technique, which by itself promises even one order of magnitude improvement in productivity, in reliability, in simplicity. Not only are there no silver bullets in view, the very nature of software makes it unlikely there will be any. Frederick Brooks, The Mythical Man Month

5. Software Characteristics • Software is a crucial element of our society. • Software is becoming ubiquitous and invisible. • Software is both a product and a vehicle for delivering a product. • Software consists of programs, documents, and data. • Software is developed or engineered, not manufactured. • Software is primarily custom-built, not assembled from existing components. • Software deteriorates, but doesn’t “wear out.” • Software has a “chronic affliction” [Pressman 5th Ed].

6. Software Death [Adapted from Figure 1.2, Pressman5E]

7. Ran on single processor, usually a mainframe Input was linear, sequential Output was alphanumeric System design dominated by Transform systems Transaction systems Delivered across a network; distributed, multiple processors; client-server. Input often from multiple concurrent sources Output must meet demands for sophisticated visualization In addition to functional requirements, must also address: network control security UI issues data/object management Software Has Changed Then: Now: Demarco: We’ve solved the easy problems first. The ones that are left are the hard ones.

8. Major Agents of Change • Compressed time-to-market, tight labor market • Hardware costs down, software costs up • Powerful computing in small boxes • Pervasive networking • Ubiquity of object technology • Expectation of sophisticated GUIs • Inappropriateness of classic software development process Adapted from “Toward a Discipline of Software Engineering,” IEEE Software, Vol. 13, No. 6.

9. Problems • Many critical systems are controlled or influenced by legacy software which is difficult or impossible to maintain, not understandable, or irreplaceable. • Little data exists on the process of developing software. • Software quality is difficult to define and measure. • Software doesn’t have spare parts. • Software project managers are sometimes far removed from software development. • Software developers are sometimes unaware of engineering approaches to developing software. • Programming as an art versus programming as a science. • Many myths pervade the software development culture.

10. … I would try to make some improvements in the codes. Many codes or subroutines are more than 40 years old, and the guys who wrote them are either in heaven or hell. Some codes are impossible to refine because nobody knows what the original programmer was trying to do. To figure it out, you have to read the code in FORTRAN line by line, to try to understand the underlying mathematics picture – and these codes are hundreds of thousands, even millions of line long. Once someone found a bug in the code and removed it – but then the code wouldn’t work. So they put the bug back in, even though no one knew why the program work that way. (by a nuclear scientist) - Page 113, My Country verse Me, Dr. Wen-ho Lee, Hyperion Pub., 2001

11. Myths • A general statement of objectives is enough to get going. Fill in the details later. • Project requirements continually change, but change can be easily accommodated because software is flexible. • Once a program is developed, tested, and delivered, the developer’s job is done. • Until a program is running, there is no way to assess its quality. • The only deliverable for a successful project is a working program. • We can always add more programmers if the project gets behind. • All programmers are created equal. [Adapted from public domain SEI course notes by Carter and Conn]

12. What is Software Engineering? design CASE coding maintenance KLOC structured analysis software quality assurance testing dataflow diagrams project management requirements metrics configuration management structure charts

13. tools methods process a focus on quality Software Engineering • The establishment and use of sound engineering principles in order to obtain economically software that is reliable and works efficiently on real machines. [Bauer] • The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software; that is, the application of engineering to software. [IEEE Standard 610.12-1990] [Adapted from Pressman 5th Ed]

14. Principles of Software Engineering • Abstraction • Analysis and Design Methods and Notations • Prototyping • Software Architecture • Reuse • Measurement • Tools and Environments • Software Process Adapted from “Toward a Discipline of Software Engineering,” IEEE Software, Vol. 13, No. 6.

15. Principles • Abstraction • Primary tool for managing complexity • View a system in terms of layers or a hierarchy or abstraction

16. Principles • Analysis and Design Methods and Notations • Notations • A formal way of documenting and communicating design decisions • Issues: Cognitive aspects, readership skills, no standards • Methods • A formal or semi-formal approach to building models • Allows for completeness and consistency checks (ideally)

17. Principles • Prototyping • Help identify requirements • Explore feasibility • Simulate functions to be implemented in hardware

18. Principles • Software Architecture • Specifies a system in terms of architectural units and how they relate • Good architecture aids implementation, testing, maintenance • Becoming a sub-discipline (e.g., Garlan and Shaw)

19. Principles • Reuse • Make use of commonalities among systems to reuse requirements, designs, code, test scripts, etc. • Reusable components can be a business asset • Barriers to reuse: • Can be faster to build a small component from scratch • May take extra time to build a reusable component • Potential adopters may hesitate due to SQA concerns • Liability issues in the event of failure or needed updates • Program understanding issues

20. Principles • Measurement • Quantification of attributes of product and process • Critical for assessment and improvement

21. Principles • Tools and Environments • Automated Software Engineering • Vertical v. Horizontal tools • Critical issues include • Integration • repositories

22. Principles • Software Process • The organization and discipline of the activities of developing software • Process diversity needed