It can be conceptual or real.
Sometimes it can be useful to expand the boundaries of the System we look at, to better understand how what we are developing interacts with other systems.
At other times it can be useful to contract the boundaries of the System, so as not to get overwhelmed.
In Planguage, a System can be described fundamentally by a set of Attributes. The Attributes are of the following types:
• Function: ‘what’ the System does
• Values: ‘how good’
• Development Resource: ‘at what cost’ (resource expenditure)
• Solution: ‘by what means’
All these specifications (the Attributes and the additional factors) are qualified by time, place and event conditions.
2. Svein Øvergaard, a Norwegian professor Client of mine said (about 1969) that he detested the word ‘system’ because it “had the precision of the word ‘thing’”. I have ever since then been careful using it and hope the Planguage definition limits the Scope somewhat.
3. Here are some Standard definitions of ‘system’:
Standard Definition [System, ISO 9000, 2000]:
“An object consisting of interrelated or interacting elements”
Note, this ISO 9000 definition emphasizes the internal relationship or interaction of System elements. This has limited interest. The most central aspect of systems is how they are externally experienced and perceived by other systems, so the Planguage definition emphasizes the Attributes, and admits the possibility of all manner of description, including the ‘interacting elements’ – but chooses to emphasize real-world ‘interaction’ (between any one System and all others).
Standard Definition [System, EIA/IS-731.1, 1996 Interim Standard]:
“system: The aggregation of end products and enabling products that achieve a given purpose.”
Note in this EIA/IS-731.1 System definition, the Concept of ‘purpose’ comes in. However, lost is the possibility of multiple Stakeholders and multiple purposes through time.
Note In practice, a System is ‘in the eye of the beholder’ and the interpretation of its meaning is frequently clarified by the use of an associative noun, e.g. Product System, aircraft System. Alternatively, the word System may be substituted simply by a context-dependent synonym, e.g. Product, aircraft, though this may then obscure a System principles perspective.”
Note in this IEC 15288 definition, the Authors seem to see a problem with the Concept, but try to solve it by encouraging specific adjectives to describe it. They stick to the official Version [ISO] but do not mention Attributes or purposes. A hint about systems principles is given.
An integrated composite of people, products, and Processes that
provide a capability to satisfy a stated need or objective.
Note this MIL-STD 499B definition is unnecessarily narrow (It does not include the Planetary System or the molecular System. ☺ ) and unnecessarily broad (a people or Product or Process would be sufficiently narrow for many systems Engineering purposes). It is good that it mentions the capability to satisfy Requirements, but some systems have capabilities that satisfy nobody’s Requirements (like faults and side effects). Systems are as they are, whether we like it or not. We have to be able to understand and describe their Attributes realistically, like them or not.
4. When defining a System, it is important to decide the relationship between the System being observed and changed, and the System of the people (the project) bringing about any change. Numerous different relationships can exist. At one extreme, a project can be completely within the System being modified. At another extreme, a project might be developing a Product System to be sold into various, as yet unknown, target systems.
2003: A System is any useful subset of the universe that we choose to specify. It can be conceptual or real.