SYSTEM organized set of related components established to accomplish certain task Natural Planned and placed by peopleSYSTEMS ANALYSIS AND DESIGN (SAD)

SYSTEMS ANALYSISProcess of studying an existing system to determine how it works and how it meets user needsSYSTEMS DESIGNProcess of developing a plan for an improved system, based upon the results of the systems analysis

An organizational process used to develop and maintain computer-based information systems (both business and systems professionals participate in SSAD). STRUCTURED SYSTEM ANALYSIS AND DESIGN

The three most important techniques that are used in SSADM are:

Logical data modeling

The process of identifying, modeling and documenting the data requirements of the system being designed. The result is a data model containing entities (things about which a business needs to record information), attributes (facts about the entities) and relationships (associations between the entities).

Data Flow Modeling

The process of identifying, modeling and documenting how data moves around an information system. Data Flow Modeling examines processes (activities that transform data from one form to another), data stores (the holding areas for data), external entities (what sends data into a system or receives data from a system), and data flows (routes by which data can flow).

Entity Event Modeling

A two-stranded process: Entity Behavior Modeling, identifying, modeling and documenting the events that affect each entity and the sequence (or life history) in which these events occur, and Event Modeling, designing for each event the process to coordinate entity life histories.

STAGESThe SSADM method involves the application of a sequence of analysis, documentation and design tasks concerned with the following.

Stage 0 Feasibility study

Stage 1 Investigation of the current environment

Stage 2 Business system options

Stage 3 Requirements specification

Stage 4 Technical system options

Stage 5 Logical design

Stage 6 Physical design

ADVANTAGES AND DISADVANTAGES

A methodological approach of studying a business from a number of different perspectives is more likely to provide a more thorough understanding of the business, its processes and data, than the "ad-hoc" approaches that were used previously. This in turn should (it was hoped) lead to systems that are more complete and correct.

SSADM approach of having to complete one phase before beginning the next led some projects into what is referred to as "analysis paralysis". What is meant by this is that because a business and its processes never stays the same for very long, the systems team would continually have to revisit analysis and design products for amendment, causing delays in getting to the programming and delivery stages of the system.

There is also a cost in training people to use the techniques. The learning curve can be considerable if the full method is used, as not only are there several modelling techniques to come to terms with, but there are also a lot of standards for the preparation and presentation of documents.

Aprototypeis an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from. It is a term used in a variety of contexts includingsemantics, design,electronics, andsoftware programming. A prototype is designed to test and trial a new design to enhance precision by system analysts and users. Prototyping serves to provide specifications for a real, working system rather than a theoretical one.

Diagram of Prototype model:

A CASE tool is a computer-based product aimed at supporting one or more software engineering activities within a software development process. Computer-Aided Software Engineering tools are those software which are used in any and all phases of developing an information system, including analysis, design and programming. For example, data dictionaries and diagramming tools aid in the analysis and

UpperCASE Tool

LowerCASE Tool

I CASE

The Waterfall Model was first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very simple to understand and use. In a waterfall model, each phase must be completed fully before the next phase can begin. At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project. In waterfall model phases do not overlap.

Simple and easy to understand and use.Easy to manage due to the rigidity of the model each phase has specific deliverables and a review process.Phases are processed and completed one at a time.Works well for smaller projects where requirements are very well understood.

Agile development model is also a type of Incremental model. Software is developed in incremental, rapid cycles. This results in small incremental releases with each release building on previous functionality. Each release is thoroughly tested to ensure software quality is maintained. It is used for time critical applications. Extreme Programming (XP) is currently one of the most well known agile development life cycle model.

*When a feasibility study is carried out, there are four main areas of consideration:Technical is the project technically possible? Financial can the business afford to carry out the project? Organizational will the new system be compatible with existing practices? Ethical is the impact of the new system socially acceptable?Stage 1 Investigation of the current environmentThe developers of SSADM understood that though the tasks and objectives of a new system may be radically different from the old system, the underlying data will probably change very little. By coming to a full understanding of the data requirements at an early stage, the remaining analysis and design stages can be built up on a firm foundation.**