SYSTEM DESIGN

OVERVIEW ON SYSTEM DESIGN• Systems design is the process of defining the architecture,

components, modules, interfaces, and data for a system to satisfy specified requirements. Systems design could be seen as the application of systems theory to product development. There is some overlap with the disciplines of systems analysis, systems architecture and systems engineering.• Systems design is therefore the process of defining and

developing systems to satisfy specified requirements of the user.

WHAT DOES SYSTEM DESIGN MEAN?• System design is the process of defining the elements of a

system such as the architecture, modules and components, the different interfaces of those components and the data that goes through that system. It is meant to satisfy specific needs and requirements of a business or organization through the engineering of a coherent and well-running system.

SYSTEM DESIGN EXPLAINED IN MORE DETAIL• Systems design implies a systematic approach to the design

of a system. It may take a bottom-up or top-down approach, but either way the process is systematic wherein it takes into account all related variables of the system that needs to be created—from the architecture, to the required hardware and software, right down to the data and how it travels and transforms throughout its travel through the system. Systems design then overlaps with systems analysis, systems engineering and systems architecture.

SSADM - STRUCTURED SYSTEMS ANALYSIS AND DESIGN METHOD• Short for Structured Systems Analysis and Design Method, a

set of standards developed in the early 1980s for systems analysis and application design widely used for government computing projects in the United Kingdom. SSADM uses a combination of text and diagrams throughout the whole life cycle of a systemdesign, from the initial design idea to the actual physical design of the application.

CONTINUATION• SSADM uses a combination of three techniques:• Logical Data Modeling -- the process of identifying, modeling and documenting

the data requirements of the system being designed. The data is separated into entities (things about which a business needs to record information) and relationships(the 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 Behavior Modeling -- the process of identifying, modeling and

documenting the events that affect each entity and the sequence in which these events occur.

SSADM application development projects are divided into five modules that are further broken down into a hierarchy of stages, steps and tasks:Feasibility Study-- the business area is analyzed to determine whether a system can cost effectively support the business requirements.Requirements Analysis-- the requirements of the system to be developed are identified and the current business environment is modeled in terms of the processes carried out and the data structures involved.Requirements Specification-- detailed functional and non-functional requirements are identified and new techniques are introduced to define the required processing and data structures.Logical System Specification-- technical systems options are produced and the logical design of update and enquiry processing and system dialogues.Physical Design -- a physical database design and a set of program specifications are created using the logical system specification and technical system specification.Unlike rapid application development, which conducts steps in parallel, SSADM builds each step on the work that was prescribed in the previous step with no deviation from the model. Because of the rigid structure of the methodology, SSADM is praised for its control over projects and its ability to develop better quality systems.