The be used to design the system. They

The systems developmentlife cycle (SDLC),also referred to as the applicationdevelopment life-cycle,is a term used insystems engineering, information systems and software engineering to describe a process for planning,creating, testing, and deploying an information system.          Identify SystemRequirements/SpecificationsOnce the aims andobjectives of the system have been made, the user requirements need to beobtained. The user requirements must be clearly stated and understood by boththe user and system developers otherwise there can be issues later on in theprocess.  This means the user andprogrammer need to negotiate the user requirements – this is done using keyquestions such as ‘What are the aims of the system?’, ‘How does the currentsystem work?’ and ‘What external systems does the new system need to interfacewith?’The designers andprogrammers must know what the aims of the system are in order to create a setof system requirements which will be used to design the system.

They also needto know why the system is being created as this will help the system to bedesign and also maintain focus on the objective of the system throughout theprocess. They also need to knowabout the old/current system so that the new system can preserve the originaland essential features of the old system. This means the new software can stopthe problems the current system being used is facing.The designers need to knowwhat other systems the new system will be interacting with so that theyunderstand the inputs from other systems going into the new one. The new systemneeds to be able to work alongside these systems without any problems.     Design the SystemThe designers use the scopeand requirements to produce a clear design for the system which will be used bythe programmers to create the system.

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The design process requires a userinterface to be designed, consideration into how the program will be structuredwith detailed on the procedures and where the data is stored within system. Thedesigns must be detailed and revised before they are given to the programmersto ensure that all the requirements for the system are met.There are a variety oftools that can be used to help create the system’s design; includingpseudocode, data flow diagrams and entity relationship models, and structurediagrams. These tools are described later on in the manual.Code the ProgramAfter the designs for thesystem has been created, the programmers can start to produce the programs andsoftware that the system will use.

If the designers used pseudocode as one oftheir design tools, the coding of the system will be much simpler as the codehas already been created in a basic from – the programmers just have to changethe pseudocode instructions such as ‘Input name’ into code like’Console.WriteLine(“Enter name”)’. The coding language used to code the programdepends on the type of system and features that it will contain; the languagecould be event-driven, object-orientated or procedural. Test the ProgramWhen the program has codedit must be tested to ensure that it has no bugs, errors or other issues.

Testing should occur once a procedure or a major part of the system has beenfinished. By testing the program as it is developed, any bugs or issues withthe programming are detected and rectified before they can cause a problem. Ifthe testing is left until the end of the coding stage in the lifecycle, theprogrammers may find they have made an error which may need a small section orpossibly the whole system to be recoded.Testing is important as itensures that a program is of high quality and will not cause any issues when itis distributed and used by the users. Another reason testing must be carriedout is to ensure that the program meets the requirements set at the start ofthis process. If the requirements are not met, then the code will need to beadapted to suit the missed requirements.Maintain the SystemAfter a program has beencreated, distributed and installed, it will be used by the user for a longtime. Over this long period of time, issue or bugs that were not found in thetesting stage or that have developed over time may present themselves.

Thismeans that regular maintenance of the system will need to take place. Maintaining the system isvital if the system is to be used for a long time as any problems will need tobe eradicated – this involve having programmers make adjustments to the code.The quality of the code will affect how much maintenance the system willrequire and for how long – high quality code will encounter less issues andwill not need have as much maintenance carried out on it compared to lowquality code. If an issue occurs with high quality code, it tends to be easilyfixed and in a short amount of time as there will be certain features thatquality code has which will make it easier to locate and fix problems. Lowquality code may encounter more problems and be more difficult to maintain asit can be difficult to locate any issues and if the programmer fixing thesystem doesn’t know how the code works, the problems might not beresolved.   System Development Life cycle Software StructureWhen creating a program, using the various differentsoftware structures related to the different programming paradigms can improvethe quality of code.

Software structures also improve the readability of code,can make validation user inputs easier and are also considered good programmingpractice. The different software structures are described below.FunctionsFunctions are modules of code that carry out apredefined task. Typically a function takes input and processes it – thefunction will define what happens to the input – and then outputs it again.Functions can be used multiple times in a program, and can be called withinother functions. In most programming languages there are two typesof function: built-in functions and user-defined functions. Built-in functionsare a part of the language and can be useful for validation, making all userinputs the same format for example. Commonly used built-in functions in theprogramming language C# are ‘.

Length ()’, ‘.To Lower ()’, ‘Random ()’, ‘.To Upper()’, ‘.

Substring ()’ and there are many others. User-defined functions arefunctions that are programmed by the user. These functions are similar tobuilt-in function but are defined outside the main body of code; they arecalled in a similar way. ProceduresA procedure, otherwise known as a subroutine, is acode module that executes a task that is not part of the main source code. Aprocedure can be called from the source code to carry out a function or smalltask. Procedures can be used to structure a program and make the source codeeasier to read. Using procedures can improve the quality of code as the programis well structured, is easily readable, and the use of procedures can help makeidentifying and resolving bug problems easier as the code is easier to access.

  Classes and ObjectsClasses and objects arecommonly used in object-orientated programming (e.g. a Windows Formapplication). Software objects are like entities – they are real-world objectsthat are being used in a system or database.

A class is the section of codewhere the programming for the object occurs. Within a class there areattributes and methods; attributes are pieces of data associated with the classand methods are the functions of the class. Classes define the differentattributes and methods, and uses objects to link them together within theclass.Object-orientated systemsuse message passing to get classes to communicate with each other and execute acommand. A class calls a function within one of its methods to gain anattribute etc. from another class – it is the only way that objects can accessthe attributes within its class.

This is how object-orientated programs differfrom procedural and event-driven programs. Using objects inprogramming improves a user’s understanding of the program as they can easilyidentify the real-world objects (the ‘variables’ in other programmingparadigms) – thus improving the readability of the code. Tools Used in the Design Stage during the design stagethere are a number of tools that can be used to develop a program. Structurediagrams, data flow diagrams and entity relationship models, and pseudocodealgorithms are some common tools used to plan a program. These tools are usedto help programmers create a design from the requirements and model a piece ofsoftware or code. The type of design tool used depends on the programminglanguage as some tools are for event-driven programming, others for proceduralor object-orientated.

StructureDiagrams Structure diagrams are abasic diagram that can be used to display the different parts of the programthat will be created (e.g. the different procedures that will make up theprogram). It can be used to define the process of creating the program inmanageable steps.

Alternatively structure diagrams can be used to model thedifferent processes and paths in the program such as loops and sub routines.When the lifecycle moves onto the coding stage, the diagrams can be used totransfer the design to code. 

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