The Software Development Process Systems analysis Systems design Implementation Testing Documentation Evaluation Maintenance 1 Systems Analysis What is a systems analyst?  A systems analyst observes, clarifies and models an existing system to assess its suitability for computerisation. In the process, the analyst could also find ways of improving the system.  The systems analyst must have a sound technical background. They may once have been programmers. 2 Skills and techniques of the Systems Analyst The systems analyst must extract the clients needs document these needs in a formal way communicate these to the designers 3 Extracting the Clients Needs Extracting the clients needs is known as requirements elicitation. This is done by:  Interviewing the client’s management personnel  Making observation notes of the client’s business  The analyst will also inspect information sources used by the client to keep track of their business. From this the Software Specification is created. This is a legal binding document between client and sw company 4 The Requirements Specification   is the end result of the requirements elicitation is a written statement of what the design team must go on to make It is extremely important to get this document right. Mistakes made later can be very costly. 5 Documentation The systems analyst must document the clients needs by drafting formal reports:  requirements specification  system specification 6 Design Representations There are a number of commonly used forms of design representation in common use. Examples include:  structure diagrams  pseudocode 7 Structure Diagram A commonly used syntax for structure diagrams is as follows: A procedure A decision A loop A single task 8 An example: A structure diagram allows the design of a program to be drawn out in diagrammatic form. Here is an example: Tax payment IF earns > 30000 Get details NO Low rate payable Display amount to be paid YES High rate payable 9 Pseudocode Pseudocode is another example of a method of describing a program. Simple English words are used to describe the steps of the algorithm and any refinements made. 10 Pseudocode - Example 1. 2. 3. 4. Display information Get details Do calculation Display answer Refine 2.1 2.2 2.3 Notice the numbering system 2.4 2.5 2.6 step 2 display prompt get value while value out of range display error message get value loop Top level design Simple English words in a familiar program form 11 Hierarchy of Software  A diagram of the hierarchy of software will   show the relationship between all the modules of the software identify modules which contain a call to other sub modules. 12 An Iterative process It is important to realise that the software development process is iterative in nature. This means that the problem will be revisited a number of times getting closer and closer to the required solution on each time round. 13 CASE Tools CASE stands for “Computer Aided Software Engineering”. A CASE TOOL KIT is a set of integrated CASE tools that have been designed to work together and to automate (or provide automated assistance for) the entire software life cycle, including analysis, design, coding and testing. Using such a toolkit speeds up the development process in a number of important ways. 14 Fact Finding Analysis is a fact-finding process, and there are five key questions that need to be asked, often repeatedly. These key questions are:  WHO?  WHAT?  WHERE?  WHEN?  WHY? 15 Designing the Solution Once the needs of the user are clearly understood and documented, software development can move onto the next stage, involving the DESIGN of the system. Design of the User Interface Design of the structure of the software Design of the detailed logic of the software 16 Implementation The next stage involves turning the carefully structured design into a working solution. 17 Choosing an Environment Before we can implement a solution we must decide on the programming environment which is most suitable. Languages are generally designed for a specific purpose. 18 Programming Languages Language Algol Cobol Comal BASIC Fortran Java Pascal Prolog Purpose Science Business Education Education Science and Maths multimedia Education Artificial Intelligence 19 Things to Remember...    The code should be modular, - procedures and functions should be used. Library modules should be ‘closed’ so that the variables used in them cannot disturb the code of the rest of the program. Meaningful variable names should be used. There should be internal commentary, explaining what each section of the code does. Where a complex algorithm has been implemented, it is helpful to comment on several lines of the code, in addition to a general description of what the module does. 20 Things to Remember (2)   Where parameters are being used in a module, they should be described in the commentary of the module. This is particularly important in library modules. Parameter lists should be small and manageable. If a procedure or function requires a set of parameters which is very big, then it is likely that it is performing more than one program function. The original design needs to be revisited, and functionally decomposed. 21 Debugging the Solution A common technique in trying to debug a piece of software is to conduct a structured walkthrough (step through each line of logic in the code) using a structured listing, which is simply a formatted display or printout of the code. It is important that the code is written in such a way that helps the above activities. 22 Dry Runs To complete a dry run the programmer works through a section of program code by hand. This is very useful for locating errors in both syntax and semantics. A trace table will normally be used in this activity. 23 Trace Tables A trace table is Line no Length Breadth Area constructed with a 1 5 column to identify 2 4 3 20 the instruction 4 20 executed and a column for each variable. The programmer works through each line of the listing changing the appropriate variables. 24 Test Data The expected results from a test data set must be known in advance, so that they can be checked against the actual results. You should include test data to demonstrate the following: 1. “normal” operation of the software, to make sure that there are no unexpected results in ordinary work. 2. the operation limits of the software, to make sure that the boundary conditions identified in the design stage are being handled properly. 3. “exceptions” to the normal operating conditions. This set will show whether or not the software can react to unexpected inputs in an effective way, without crashing. 25 Documentation The User Guide   This document should describe how to use the software. Ideally there should also be tutorial files which can take the user through examples of a piece of work, and allow them to become familiar with the commands, and the various sections of the software. 26 Documentation The Technical Guide This document should provide information on  how to install the software  hardware requirements  software requirements 27 Evaluation  Does the solution meet the user requirements?  Judge this against a set of criteria         screen layout help required user prompts fitness for purpose maintainability robustness reliability portability 28 Some Definitions  Correctness   A program is correct if it matches the users requirements Maintainability  A program will be easily maintained if it has been written in a way which will make it easy to change. This will include    internal commentary meaningful variable and procedure names parameter passing 29 Some Definitions (2)  Reliability   A program is reliable if it is free from bugs, ie it must meet the requirements repeatedly under severe testing Readability  A program is readable if it is easily understandable by people other than the original programmer, ie good internal documentation, use of white space, etc. 30 Some Definitions (3)  Portability   A program is said to be portable if it can be transferred from one system to another with minimal adaptation Efficiency  A program is efficient if it uses the most appropriate structures for the job. It should run as fast as possible and not use up more system resources than are necessary. 31 Some Definitions (4)  Robustness   A program is said to be robust if it does not crash when invalid data is input or unexpected results are generated. Fitness for Purpose  Does the program meet the requirements? 32 Maintenance  Activities identified as part of maintenance:    corrective (17%) adaptive (18%) Perfective (65%) 70 65 60 50 40 30 20 17 18 10 0 % 33 Maintenance Costs  Maintenance is very costly. It is vital that errors are detected at as early a stage as possible. 100 90 80 70 60 50 40 30 20 10 0 1970s 1980s 2030 ? % of total development cost 34 Factors Affecting Maintainability       The application being supported staff mobility too many versions not enough documentation dependence on external environment hardware and software stability 35