Definition of System
Definition Last Updated 17-Dec-2015 12:51
A system is a collection of physical entities, which may be individually referred to as resources or components of the system, having specific attributes (including both physical characteristics and behaviours) that, working together in a defined context, deliver a specific set of .
The name of a system is a reference to the complete working set of components. Membership of a system is non-exclusive: a resource or component may belong to more than one system simultaneously.
The physicality of systems does not exclude software, applications etc.; these are included as behaviours of systems arising from compliance with behavioural specifications, i.e. code, applications etc. do not have independent functional existence.
Article Last Updated 17-Dec-2015 12:51
The phrase working together in the definition implies dependency relationships between the components of the system; the defined context implies the existence of constraints and dependencies on the environment, which constitute a set of preconditions to be satisfied for the nominal operation of the system and satisfactory performance of the required capabilities.
The reference to the physicality of the entities does not preclude entities such as specification, i.e. the enumeration of instructions for a processor to execute, those instructions only have effect by virtue of their existence as patterns of charge or magnetic fields or other tangible things in various devices, which patterns encode the instructions and are interpreted by the processor.from being considered parts of a system. Whilst software may be considered as an abstract
Because a system actually delivers specific capabilities it is in one sense self-contained; one cannot however entirely neglect the dependencies (also expressible as constraints or assumptions) given by the context, which may show that the system is not absolutely self-contained because it depends, for example, on the availability of electricity.
Different system definitions are therefore compatible (for the purposes of comparison and consideration of content) only to the extent that the contexts are compatible; ideally, a collection of systems should only be discussed as a whole if they share a single common context.
Because a set is a conceptual grouping, membership of one set does not necessarily preclude simultaneous membership of other sets, i.e. systems may overlap. The extent to which system overlaps affect performance will depend upon the specific nature of the things: execution of a process specification in one place need not impinge upon the execution of that process.
The term system may mean a wide variety of things according to context; the application AutoCAD may be described as the “building drawing system”; a database of parking permissions may be referred to as the “Parking System”; Microsoft Excel might be referred to as a “spreadsheet system” and so on.
However, what all such usages have in common is that in each the system is the sole, or at least primary, component of a collection of things (that may include people) that realises a recognised capability.
It is essential to recognise that to designate a collection of things as a system is to create a conceptual boundary dividing the things that are in the system from those that are not; it is equally important to recognise that as a purely conceptual boundary, any one thing may be part of more than one system – systems are not necessarily physically disjoint (non-overlapping). Since Microsoft Excel must run on a computer, under an operating system, my “spreadsheet system,” – of which Excel is merely the most prominent part – significantly overlaps with my “word processing system,” which comprises Microsoft Word on the same computer (and, as it happens, under the same operating system).
System is therefore not a fundamental entity for architectural modelling purposes; it may be natural to draw a box and label it “System X” but the arbitrariness of the boundary should not be forgotten. Ideally, there should be specific reference to the context in which the boundary is defined.
Most systems do not have people in them, but – in English at least – it would be perfectly legitimate to refer to the “British Legal System” and thereby refer to the laws, the judicial bodies and the judges, magistrates, lawyers and others who may be said to operate the system from within.
Similarly, most organisations are not thought of as being defined by the IT hardware they contain, but the Swiss National Supercomputing Centre could not be what it is without a supercomputer. Organisations are therefore likewise not fundamental entities; an organisation is just a particular kind of system.