1. Designing & Testing Software Development Notes Software Design & Development: Design Notations, Development Methodologies & Testing and Documenting Solutions

2. Contents The Software Development Process  Questions Questions Development Methodologies  Questions Questions Design Notations  Questions Questions Errors and Bugs  Questions Questions Testing Techniques  Questions Questions

3. Software Development Process The software development process is a seven step process that programmers usually follow when creating software. Some development methodologies don’t follow all of these steps though. The process is sometimes referred to as the waterfall model – as once you have completed one step, you move onto the next The steps are  Analysis  Design  Implementation  Testing  Documentation  Evaluation  Maintenance

4. Iteration The basic waterfall model is simplistic. In practice, iteration is used to improve the quality of the created software In iterative software development, earlier phases of the development process can be redone based on what has been learned later. In other words, you can go back up the waterfall! Analysis Design Implementation Testing Documentation Evaluation Maintenance

5. Analysis The Analysis stage is where you identify what the program is going to do. The analysis stage usually requires the participation of two parties – the systems analyst and the client The client is a person or group who the software is being made for. The client usually has a good idea of what they want the software to do, but may not be able to express it well The systems analyst is a person or group whose job it is to identify what the clients requirements are. Systems analysts require both a strong understanding of computing and interpersonal skills to elicit information from the client Methods used by the systems analyst might include:  Interviews – with both managers and workers for the client  Observations of existing working practice  Questionnaires

6. Software Specification At the end of the analysis stage, the systems analyst and the client will have agreed upon a software specification document The software specification is a legally binding document. It is a contract which states what the software is going to do, and how much the software developers will be paid for creating it for the client.

7. Design In the design stage, the software specification is used to plan out how to create the software, and how it will do the tasks required of it. Different design notations will be used to create different parts of the design:  The user interface can be designed using wireframing  Individual subprograms can be designed using pseudocode Depending on the development methodology used, a design document may be produced at this stage. While the software specification states what the software has to do, the design documentation will state how it does it

8. Implementation In the implementation stage, the software is created The project manager in charge of creating the software has to manage the implementation stage. They have to lead a team or teams of programmers to create the software. Many factors have to be considered when implementing software:  What programming language will be used  Who is going to program which part of the program  Do additional programmers need to be hired? Will currently hired programmers require additional training?  What is the timescale for producing the software, and is the programming team keeping to the timescale  What is the budget for creating the software, and is it being kept to

9. Testing In the testing stage, the software is tested to make sure it is working correctly. Software needs to be reliable, robust and fit for purpose Reliable software processes data correctly. Robust software is can cope with errors when it runs – it does not crash unexpectedly Fit for purpose software fulfils the requirements set out in the software specification Testing will be examined in more detail in a later section

10. Documentation Once software is “complete”, it can be documented. A number of different documents might be created The user guide or manual tells the user how to complete certain tasks with the software. The user guide is written for typical users and does not require significant computer expertise to understand Technical documentation covers technical information about the software, such as configuration, system requirements and application programming interface (API) documents for the software Technical documents are written for expert users and other programmers so they can modify the software

11. Evaluation In the evaluation stage, the software is judged in terms of how good it is. The most important consideration is whether or not the software is fit for purpose – does it do what it is supposed to, as set out in the software specification There are a number of factors that should be considered as well  Reliability – does the software process data correctly?  Robustness – can the software handle errors without crashing?  Efficiency – can the program process data without using to much memory / processing time?  Portability – can the software be used on different computers?  Maintainability – can the software be changed easily  Readability – is the program code easy to read, using meaningful variable and subprogram names, and internal commentary

12. Maintenance The maintenance stage happens after the software has been released or passed to the client. It covers changes made to the software during its lifetime. Corrective maintenance fixes bugs and other errors discovered in the software after release Perfective maintenance adds new features to software Adaptive maintenance changes software to allow it continue working despite changes to its environment – such as running on a updated operating system for example

13. Questions – The software Development Process Answer questions in full sentences! 1. List and briefly describe the seven steps of the software development process 2. Explain how making the development process iterative can improve the quality of software produced 3. Explain why a systems analyst needs both expert computer knowledge and interpersonal skills 4. What is a software specification and why is it important to agree on one before creating software 5. What is meant by the term “fit for purpose” when testing and evaluating software. Why is this the most important consideration when evaluating software? 6. List and describe other factors to consider when evaluating software 7. Describe two types of documentation that can be produced during the documentation stage 8. List and describe three types of maintenance

14. Development Methodologies A development methodology is the way in which software is created The waterfall model is an example of a top-down development methodology. Top-down development methodologies set out to complete the entire specification of an item of software in one go. The project is split into progressively smaller parts, with each part representing an easier subsection of the task. Once a task is split into sufficiently easy chunks, individual programmers can complete each part of it

15. This top-down approach represents the traditional method of developing software. It holds a number of advantages:  Thorough, careful and considered – clear goals at each phase of development  Clearly defined roles and specialisations – each individual knows what they are responsible for  Easy to manage, easy to keep track of where things do go wrong There are also disadvantages with this approach:  Unwieldy and prescriptive – flaws in the design are difficult to correct and may require an extensive redesign and throwing away completed code to accommodate design changes  Inefficient – can result in a lot of extra work, especially documentation, which in turn can result in software being over budget  Client sees little progress until the software is complete

16. Rapid Application Development Rapid Application Development (RAD) is an alternative development methodology intended to overcome the weaknesses of the waterfall model. In RAD, the specification and planning are less important. Prototyping is used to produce and demonstrate incrementally better versions of the software. Feedback from the clients is used to alter the requirements and improve the software User Design and Construction are iterative stages – each new software build informs the design of the next build

17. Using RAD as a development methodology has a number of advantages over the waterfall model:  The client gets to see the software very early on and has input into its progress  Client feedback results in a very good user interface  Risk factors can be identified and solved without requiring complete redesigns of the software – this makes it more likely that the software will be produced on time and on budget But reducing the importance of planning has consequences that are disadvantageous for RAD  Client has to give up more resources in terms of time and man-hours to provide the feedback  Feedback tends to focus on UI – back end code can end up poorly designed and less efficient as a result  Less control over the process – in particular since the requirements change over time, it becomes more difficult to judge if the developers have fulfilled their contract with the client

18. Agile Methodologies Agile methodologies are software development methodologies that favour adaptability and flexibility over planning and following processes. Rapid Application Development could be considered an agile methodology. There are a number of different agile methodologies such as Extreme Programming and Scrumm. They follow a number of principles:  Individuals and interactions over Processes and tools  Working software over Comprehensive documentation  Customer collaboration over Contract negotiation  Responding to change over Following a plan Pair Programming is an example of an agile technique

19. Top-Down vs Agile Top-down and agile methodologies have different strengths and weaknesses. This makes them suitable for different types of projects. Smaller to medium scale projects work well with agile methodologies. Agile techniques that rely on close collaboration amongst the development team can help make better quality software. Larger projects require more people to complete. Top down models allow much better control over larger teams because of the clearly defined roles and structures

20. Questions – Development Methodologies Answer questions in full sentences! 1. Explain what is meant by top-down software development 2. Describe the advantages of top-down development methodologies 3. Describe the disadvantages of top down development methodologies 4. What is Rapid Application Development? 5. Explain how RAD improves the quality of developed software 6. Explain how RAD can reduce the risk of cost and time overruns 7. Why might it be a problem that agile methodologies result in less control over a project than top down methodologies? 8. Why would an agile methodology be less suitable for creating an large information system for a multinational bank with offices in several countries?

21. Design Notations A design notation is a way of describing the design of a program, or part of a program There are many different design notations. Different design notations are more useful for different parts of the software  The user interface can be designed using wireframing  Individual subprograms can be designed using pseudocode It is important to select the right design notation when designing software

22. Pseudocode Pseudocode is a design notation that sets out what an algorithm will do. It uses the structure of a programming language, but uses English words instead of program code This pseudocode example shows the algorithm for iterating through an array: 1) FOR EACH name FROM names 2)RECEIVE names[i] FROM KEYBOARD 3) END FOR EACH It uses the for loop programming construct, but because the words used are closer to English, it is easier for people to understand. Pseudocode is easy to translate into a programming language – each line of pseudocode should be equivalent to a line of code in the programming language The equivalent python code

23. Stepwise Refinement In stepwise refinement, complicated pseudocode steps that would take more than one line of code are refined into further pseudocode Stepwise refinement allows bigger programs to be designed with pseudocode. It helps developers to create modular software. Refined steps are often made into subprograms This example shows how steps can be refined: 1) Set up variables 2) Get input 3) Calculate answer 4) Display answer 2.1) RECEIVE width FROM KEYBOARD 2.2) RECEIVE length FROM KEYBOARD 2.3) RECEIVE height FROM KEYBOARD The refinement as a subprogram

24. Wireframing Wireframing is a design notation for creating user interfaces. A wireframe is sketch that shows the placement of elements on the UI. The advantage of wireframing is it can be used to show to and gain feedback from the client and users very easily. It does not design the underlying program code though A wireframe and corresponding Visual Basic interface

25. Structure Diagram A structure diagram shows the relationship between a program and the subprograms that make it up, as well as the data flow between them. Structure diagrams are useful for showing the shape of a program to people who are not computer experts. The bigger a program gets, the more difficult it is to draw the diagram Volume of a cuboid Get Inputs Calculate Volume Display answer width, length, height volume

26. Flowcharts A flowchart is a graphical representation of the steps taken by a program Flow charts are useful for showing the flow of information in a program to non-experts, but they become increasingly difficult to draw as the program gets bigger Input width Is width >0 Display error message N Y This partial flowchart shows input validation Note the use of the diamond shape for decisions

27. UML Universal Modelling Language is a design notations that shows objects – classes, subprograms and database tables – as well as their attributes and relationships to each other. UML is particularly useful when designing software that includes databases, or when using object orientated programming languages

28. Questions – Design Notations Answer questions in full sentences! 1. What is pseudocode and stepwise refinement? 2. Why is stepwise refinement a useful design notation to use when using a top-down development methodology? 3. Describe an advantage of pseudocode 4. What is meant by wireframing? 5. Give one advantage and one disadvantage of wireframing 6. Explain why structure diagrams are inappropriate for designing larger programs 7. Why is a flow chart better for explaining how input validation works to a non-expert than the corresponding pseudocode 8. When might you use UML as a design notation? Why? 9. Write the pseudocode for a program that calculates the perimeter of a rectangle. Use stepwise refinement to break the pseudocode into subprograms

29. Errors and bugs During the implementation stage of creating software, it is common for the programmers to make mistakes and errors known as bugs. You are required to be able to identify such bugs where they occur, the nature of the error and correct it Bugs can be identified by testing. Software must be tested comprehensively in order to find and correct as many bugs as possible before release

30. Syntax Errors A syntax error is when the programmer has made an error in their use of the programming language. Syntax errors happen when the computer cannot understand what a line of code means. Programs will not compile or run at all if they include a syntax error. This makes it easy to know if your program has a syntax error, though it can still be difficult to find and fix Most programming environments will highlight where they have encountered the error. This might not be where you have to fix a mistake though

31. Typical causes of syntax errors include  Spelling errors – programming keywords and variable names misspelt  Missing symbols – “, &, : or other symbols have been missed out, meaning the computer can’t understand what the program says  Closure error – blocks of code haven’t been closed off properly with brackets or end statements where appropriate The missing : from the for line will cause a syntax error Many compilers will highlight the next line as being the source of the error though!

32. Execution Errors Execution Errors are bugs that will not be highlighted when the program is compiled, but will cause the program to crash whilst running Some execution errors only happen when using specific sets of input data, which can make them very hard to track down. Most programming environments will report at which line an execution error occurred

33. Typical causes of execution errors include  Spelling and naming errors – trying to access a variable or object using the wrong name may cause the program to crash.  Calculation errors – trying to perform calculations that are impossible such as dividing by 0 will cause the program to crash. The misspelt variable poeple above is assigned the value 0 instead of what the user entered. This causes a divide by 0 error which crashed the program

34. Logic Error Logic errors cause a program to process information incorrectly and give the wrong answer. Logic errors do not cause a program to crash or fail to run. Logic errors can only be spotted by testing, and may only occur with specific inputs. This makes them very hard to detect and fix. Logic errors are usually caused by bad design and lack of knowledge This logic error is caused by the programmer not understanding operator precedence

35. Questions – Errors Answer questions in full sentences! 1. Describe in detail the three types of errors in a program? 2. Why is it important to thoroughly test a program in order to catch execution and logic errors? 3. Execution and logic errors are sometimes also known as runtime errors. Why? 4. A program has been written to count the number of A grade passes in a test. It is shown below a)What is the output of the program? b)What type of error has occurred? c)Identify the line with the error in it and correct it

36. 5. A program has been written to calculate tax codes. It is shown below a)What type of error does this program include? b)Identify the lines with the error in it and correct them

37. Testing Techniques In the testing stage, software is checked to make sure that it works correctly. In order to test software, the testers must create and follow a test plan. Test data is a specific input or inputs for the program. If the program fails to process a single item of test data correctly, there is a bug that needs fixed. Once a program is able to correctly process all the test data from the test plan, it can be said to be reliable

38. Component Testing To simplify the process of testing software, individual components of the software can be tested. If a component works correctly it can integrated with the rest of the program To test an individual component of a program, the testers have to identify suitable sets of test data to use with it. A test table should be created and completed: MarkExpected resultActual result -5rejected 0accepted 4 10accepted 12rejected A test table for checking the input validation of a mark between 0 and 10. Note the normal, extreme and exceptional values

39. Comprehensive testing Test plans should be comprehensive – they should test each appropriate component with a range of appropriate values. They should also check that the software as a whole produces correct results To make a comprehensive test plan:  Identify each component to be tested  Identify test data to use with each component – normal, extreme and exceptional values  Create a set of test data to check that the program as a whole gives correct results  Work out what the expected result for each bit of test data should be

40. To follow the plan  Record the actual results for each bit of test data  Compare the expected and actual results Testing should be iterative – if the expected and actual results do not match, the program has a bug. The developers should go back to the implementation phase, fix the bug and then re- test the program In practice, component testing is carried out continuously during implementation. Programmers usually check that each module of code is working as they create it

41. Dry Runs In dry run testing, a programmer reads through pseudocode or program code, keeping track of the value or state of a variable or other object Dry run testing is useful as it can be carried out before programming has even begun. It can be used to check if an algorithm design is correct. Dry run testing is not very scalable – most people find it hard to keep track of several different values in their head at once!

42. Trace Tables A trace table is a dry run where the changes in the values of variables are recorded in a table. This makes it easier to track the progress of multiple variables 1) SET total TO 0 2) FOR counter FROM 1 TO 10 3) SET total TO total + 10 4) END FOR Note how the line numbers repeat as the loop progresses LineTotalCounter 10 201 3101 2 2 3202 2 3 3303 2 4 3404

43. Breakpoints A breakpoint is an intentional stopping point placed in a program in order to help debug the program. When run, the program will pause when it reaches the breakpoint. This allows the programmer to study the program’s environment – including information such as the values stored in variables. This lets the programmer check if the program has run correctly up to the breakpoint Once the programmer is satisfied, the program can then be continued. Some software development environments include the ability to place breakpoints in programs A breakpoint in Visual Basic

44. Questions – Testing Answer questions in full sentences! 1. What is meant by component testing? 2. Describe in detail how each individual component in a program should be tested 3. What is meant by comprehensive testing? Why is it important to test a program comprehensively? 4. The testing process is usually iterative. Why is it a good idea to carry out testing iteratively? 5. Explain what is meant by dry run testing 6. Give one advantage and one disadvantage to dry run testing 7. What is meant by a breakpoint?

45. 8. Copy and complete the trace table for the following program LineListMinimumCounter 1 2 3 5