Understanding Computer Science and Software Development

1. What is Computer Science? • The systematic study of computing systems and computation. The body of knowledge resulting from this discipline contains theories for understanding computing systems and methods; design methodology, algorithms, and tools; methods for the testing of concepts; methods of analysis and verification; and knowledge representation and implementation. • Source: http://www.hpcc.gov/pubs/blue94/section.6.html • Closer to Mathematics than other sciences • Math is declarative • CS is imperative CS1 - CS and Software Development

2. Euclid • Was a mathematician • Developed a systematic method for computing the GCD • Did not consider how his method could be implemented • Did not reason about the properties that an implementation might exhibit CS1 - CS and Software Development

3. Augusta Ada Byron • Was a Computer Scientist • Studied methods of computing (Babbage’s analytical engine) • Reasoned about the implementations and their properties CS1 - CS and Software Development

4. Areas of Computer Science • Some areas in computer science include: • Fundamental algorithm concepts • Computer organization (“von Neumann”) • Programming • Data structures and abstraction • Limits of computability • Operating systems and security • Distributed computing and networks • Models in artificial intelligence • File and database systems • Parallel computation • Note that programming is only one of these topics areas. CS1 - CS and Software Development

5. Approaches to Teaching CS • Breadth first • Cover several topic areas • Not covered in depth • Depth first • Concentrate on one topic area • Where do CS1/2/3 fall? • Depth first • Study of programming CS1 - CS and Software Development

6. Computer Engineering • Focus on the hardware • Not just assembly of pre-made components • Machine level, bit-head sort of work • Programming is done in C, or assembly language. • Might write a device driver or small OS • You “talk” to the hardware CS1 - CS and Software Development

7. The Other Three • Think about a car… • There are people who design and build cars • There are people who maintain cars and keep them running smoothly • There are people who use cars to solve problems • Delivery Company, Race Car Driver, you … CS1 - CS and Software Development

8. Information Technology • Primary focus is applying computing technology to solve problems • User-oriented • Craft Solutions using existing technology • In the Car example • Automotive Mechanics • Computing Example • Design and implement a web site CS1 - CS and Software Development

9. Computer Science • Study the science of computing • Programming • Algorithms • Theory • In the Car example • Develop more efficient engines • Computing Example • Design and build a web browser CS1 - CS and Software Development

10. Software Engineering • How to engineer software • Programming “in the large” • Process • Verification • In the car example • Build an engine that will work for 200,000 miles • Computing Example • Build an extendable web browser within 24 months CS1 - CS and Software Development

11. Code Size CS1 - CS and Software Development

12. Size Categories CS1 - CS and Software Development

13. Disasters • 7 deaths of cancer patients were due to overdoses of radiation resulting from a race condition in the Therac-25 software. • On June 4, 1996 an unmanned Ariane 5 rocket launched by the European Space Agency exploded just forty seconds after its lift-off. The destroyed rocket and its cargo were valued at $500 million. It turned out that the cause of the failure was a software error in the inertial reference system. • The 1988 shooting down of the airbus 320 by the US Vicennes was attributed to the cryptic and misleading output displayed by the tracking software. • An Iraqi scud missile hit Dhahran barracks, leaving 28 dead and 98 wounded. The incoming missile was not detected by the patriot defenses, whose clock had drifted .36 seconds during the 4-day continuous siege. CS1 - CS and Software Development

14. So What Does All This Mean? • Seat of your pants programming may work here, but it won’t cut it in industry!! • There is an urgent need to • Understand computation • Develop techniques to build and manage large software systems • Test and verify that software works correctly • This is part of what software development is all about CS1 - CS and Software Development

15. The Software Life Cycle • Requirements or analysis • Determine and spell out the details of the problem • Design • Determine how to solve the problem • Coding • Testing • Verify that the program solves the problem • Verify that the requirements have been satisfied • Maintenance CS1 - CS and Software Development

16. Waterfall Model Requirements/Analysis Design Coding Testing Maintenance CS1 - CS and Software Development

17. Documents • The work done in each stage is typically summarized in a document • Requirements document • A description of what the customers and users expect the system to do • Specifications • A detail description of how the software system will behave • Design • A description of the various components in the system and how they will interact CS1 - CS and Software Development

18. Testing • What does it mean to say a program is correct? • That it satisfies the requirements • Testing verifies that the program behaves as stated in the requirements • Note that incorrect, or incomplete requirements could result in an incorrect program CS1 - CS and Software Development

19. Debugging • Debugging is not testing • When testing you are trying to verify that the software meets the requirements • When debugging you are trying to correct an error • If you are debugging, your software is broken!! • Bugs don’t crawl into your program – you put them there – THEY ARE ERRORS!! CS1 - CS and Software Development

20. The First Bug CS1 - CS and Software Development

21. Testing is Not Easy • It is hard to come up with good test cases • The goal of testing is to find errors • Testing can never prove the absence of errors • Testing requires you to assume that you will find errors in your code CS1 - CS and Software Development

22. Types of Testing • Unit Test • The testing of individual routines and modules but not whole systems • System Test • The testing of the entire system, or a significant portion of it CS1 - CS and Software Development

23. Test Cases • Equivalence Partitioning • A good test case covers a large part of the possible input • Error guessing • Developing test cases based on where you think the errors will occur • Boundary Analysis • Write tests that exercise the boundary conditions CS1 - CS and Software Development

24. Data • Classes of bad data • Too little data • Too much data • The wrong kind of data • The wrong size of data • Classes of good data • Nominal cases • Maximum/Minimal normal CS1 - CS and Software Development

25. Show Me the Requirements • Requirements can come in many forms • Formal requirements document • Here this is a homework assignment • Module, function, class, method specifications • Pseudo-code • Logic specifications • Functional specification CS1 - CS and Software Development

26. RULE #1 • You must test every piece of code that you write for this course • If you want help from me or any of the TAs you must show test code first CS1 - CS and Software Development

27. RULE #2 • Don’t be afraid to write throw away code • When testing you will probably write code that will never “see the light of day” • You should write lots of small programs to test and that allow you to experiment with programming CS1 - CS and Software Development

28. RULE #3 • Always take baby steps • Start a task by picking the smallest easiest portion to do first • Test what you write before you move on to tackle another task • Always try to build on the simple parts that you know work correctly CS1 - CS and Software Development

29. RULE #4 • Don’t re-invent the wheel • Before writing anything – check to see if it has already been written (by you or someone else) • Feel free to re-use code (anything I post is yours to use) BUT MAKE SURE YOU CREDIT THE SOURCE CS1 - CS and Software Development