BTEC Unit 06 – Lesson 08 Principals of Software Design Mr C Johnston ICT Teacher

Session Objectives Understand the principles of software development, Understand the principles of software structure.

System Development Lifecycle Developing software is a complex process which requires a number of stages to ensure that it is successful and does what it is supposed to do, We break the process of developing software down into a number of stages known as the system lifecycle, Each stage has a specific focus to ensure that the next stage can be completed, Much of the early work is done is done by a systems analyst rather than a programmer.

System Life Cycle When developing software we follow the stages in the system lifecycle in order to complete it Identify Outline of the problem Analyse The needs of the system Evaluate / Maintain Refining the system Design Planning all parts of the system Implement Creating the system Test Making sure the system works System life cycle

Stages Identification of Problem Define the scope Analysis Gather user requirements Create Specification Design User interface Structure of program Procedure design Data structure design Implementation – Write Program Testing Evaluation and Maintenance

BTEC Book – Unit 06 p14-16 Section 2.1

Software Structures The structure of the program depends on the type of programming language been used… Procedural splits into procedures or functions whilst in OO programs are spilt into objects which are based on classes. Programming terms… Functions, Procedures, Classes and Objects, Predefined Code.

BTEC Book – Unit 06 p16-18 Section 2.2

BTEC Book – Unit 06 p14-18 Section 2.1 and Section 2.2 Presentation – Tools Used During the Investigation, Analysis and Design Stage

Creating High Code Reliable and Robust Can deal with user errors Usable Programs need to be intuitive Portable Ability to run on different hardware and software platforms Maintainable Make sure that the programs written have documentation and are easier to read Efficient Code Using loops to repeat code instead of writing the same thing several times one after the other Using subroutines to repeat code common to several sections of a program Using CASE statements instead of nested IFs

Suitable Design Defining correct data types to store things Defining variables in the correct place – as locally as possible so don’t bloat other routines, Use predefined code and functions where possible to save writing their own.

Making Code Easier To Read Using the comment facility to add comments to the programming code, Using appropriate names for variables, Indent blocks of selection and iteration code.

Use a software development application rather than a text editor, Colour codes different parts of the code to make it easier to read.

BTEC Book – Unit 06 p18-20

M1 and D1 are best combined as the topics are related. To cover M1 adequately you need to make sure you explain all the quality issues from the unit content (efficiency, reliability, robustness, usability, portability, maintainability). Remember for a merit criterion you need to provide more than a descriptive list – You need to explain why the issues discussed are important when developing software. For D1 again a descriptive list of techniques to make the code easier to read is not enough to cover this criterion. You need to discuss the issue involved, the benefits and limitations of each technique. Give examples of actual code showing the technique in use and explain what issue may arise if it is not used. P5 – Explain the role of software design principal and software structures in the IT Systems Development Lifecycle, M1 – Explain the importance of the quality of the code D1 – Discuss factors which can improve the readability of the code P5 – Explain the role of software design principal and software structures in the IT Systems Development Lifecycle, M1 – Explain the importance of the quality of the code D1 – Discuss factors which can improve the readability of the code