Software Engineering For Beginners

General Information Lecturer, Patricia O’Byrne. – Times: –See noticeboard outside School of Computing office. Notes: ering or ering eringwww.comp.dit.ie/pobyrne/software%engine ering

Reasons for Discipline Build a Lego house Build a border around a flower bed Build a garden shed Build an extension onto a house Build a house Build a multi-storey car park Scale requires discipline

Experience so far Stored program concept. File I/O. User I/O. Mainly single program systems. Scale has not been a problem.

Stored Program Concept Data area Procedural area Input Output input Output Data Instructions Program

Software System A Software System is an interrelated set of elements that are viewed as a whole and designed to achieve a purpose. It comprises:- –software –hardware –documentation –method of operation –users and operators e.g.hotel reservations system, general ledger system, POS system

Software Quality Characteristics Software correctness Reliability Efficiency Integrity Usability Maintainability Testability Flexibility Portability Interoperability Reusability Functionality

Software Engineering Software engineering is the establishment and use of sound engineering principles in order to obtain economically quality software

Three Key Elements Methods –Technical ‘how to’s for building software Project management, requirement analysis, design of data structures and algorithm procedure, coding, testing and maintenance

Three Key Elements Tools –Provide support Procedures –Sequence in which methods are applied –Documents / deliverables produced –Controls and checks ensure quality –Milestones, to manage progress

Process Models and Methodologies Software engineering process is a set of steps that encompasses methods, tool and procedures Classic life cycle or waterfall model –A software engineering process –A systematic and sequential approach to software development –Oldest and most widely used software process model

Life Cycle Divides the development of a software system into stages or phases, –For each phase the life cycle specifies Activities involved in each phase Sequence in which the activities are ordered Deliverables produced for the phase At the end of each phase a phase review meeting is scheduled –To examine the deliverables from the phase –To decide whether or not to proceed to the next phase

Life Cycle Phases Planning Feasibility study Analysis Design Code and unit test

Planning and Feasibility Planning –Problem definition defines the problem area produces written statement of current problem and objectives of system Feasibility Study –investigates whether a practical solution to the problem exists –produces a feasibility study report

Analysis and Design Analysis (What do we do?) –Fact finding investigate business process and the current system –modelling the current and required systems –deliverables - requirements specification logical models of the required system Design (How do we do it?) high level system design detailed design of components (i.e.. algorithms)

Code and Unit Test Code –programming each component of the system –Unit test - independent testing of each component –producing user documentation System Test –integrating all components and testing them together –testing to ensure that the system meets its requirements

Implementation and Maintenance Implementation –Installing the system in the ‘live’ environment –Training the users Maintenance –Changing the live system Correcting defects reported by the users Implementing enhancements requested by the users –Mini life cycle in itself

Life Cycle Support Activities Phases in the Life Cycle are complimented by a number of support activities –Project Management –Quality Assurance –Configuration Management

Project Management Co-ordination and control of the people involved in the development Includes Budgeting Scheduling Monitoring progress Reporting status Corrective action

Quality Assurance Ensuring, verifying and maintaining the quality of the system to be delivered Includes –Performing reviews –Testing

Configuration Management Management of the documentation and code that is produced Include procedure for –Storage –Retrieval –Control of change

Simplified System Life Cycle Iterative process Client Requirements Specification of Requirements Technical Specification Working System Operational ‘Live’ System Analysis Design Code Install Test Validate Measure Meets

Advantages Advantages of a defined, agreed and documented approach –Consistent approach to software development is achieved –Improved communication between developers –Better control of progress by using each phase as a milestone or checkpoint