Posts Tagged ‘Systems’


It’s Just A Dependancy

July 17, 2011

Peter RabbitThe rabbits in my garden are eating my carrot shoots, in the best traditions of Peter Rabbit. Unlike Farmer McGregor my livelihood does not depend on carrots; if it comes to that I don’t particularly like them, but I have a garden and apparently you should grow vegetables in it.

We can say that the rabbits depend on my carrot shoots to live. Yet if I stop growing carrots, the rabbits will not starve: they will eat something else. Probably whatever it is I try to grow instead of the carrots. If that’s not palatable, then they will no doubt eat something else, even if it’s not as tasty. They may even find something else that is more tasty, more nutritious, or more sleeky on the fur.

Carrot shoot

In other words, any observer can see that they depend on the carrot shoots for food for their current lifestyle. But it’s not an obvious step – it requires domain knowledge – to realise that not growing carrots will not cause the rabbits to starve to death (which is different from rabbit starvation). It is a resilient system, at least as far as the rabbits are concerned.

However another view is that any change results in a change of system. If I concrete over the vegetable patch, the rabbits will resort to grazing the lawn, but this is a different system. Even replacing carrots with potatoes will result in slight changes in nutrition which will in turn feed (ha ha) other consequences. In other words, the old system breaks easily at the slightest disturbance and has to be replaced by a new one – it is a fragile system.

These two rather distinct ways of looking at the same system can result in very different assessments. During and after the ‘credit crisis’ the term ‘house of cards’ was frequently used to talk about modern economies, as if the failure of a few companies within a few industries could destroy the whole practice of using tokens to describe the values of things we exchange. There are similar (anecdotal) concerns about ‘oil’, or ‘food’ or ‘our whole way of life’, backed by descriptions of the current set up and how easy it would be to attack a point on it. The ‘delicate balance of nature’ too is cast in the frame of a ‘fragile’ system where any disturbance causes failure; this is awkward as nature’s chaotic, er, nature, means that its various subsystems disturb each other all the time.

When assessing the resilience or fragility of a system we need to assess not the dependencies of the moment – the instances – but the outcomes of change to the various participants. This too is not straightforward as many systems have multiple participants with several interrelated goals, and most users have several available systems to draw on. It’s not enough to just pick on particular harms; these have to be traded off against benefits and other harms, and don’t forget those of not changing the system.

For example, I can fence the vegetable patch which would improve my garden system in my favour, but not the rabbits’. The rabbits can eat something else.

But then, so can I:

Rabbits & Carrot


When are Systems Of Systems not Systems?

November 26, 2010

Only the most trivial of systems are not composed of other systems, yet the term ‘System of Systems’ is used as if describing something distinct. So what is it? What’s the difference between a ‘system of systems’ and a ‘system of … things that aren’t systems’?

Is it a bigger thing?

For example, this paper (Net-Centric, Enterprise-Wide System-of-Systems Engineering And The Global Information Grid PDF) argues that systems-of-systems are not just a scaling up of systems-of-components but are distinguishable as follows (click to enlarge):

Yet plainly many of these are simply differences of scale:

Local vs global is a simple geographic scaling, and is not really valid, depending on how you define ‘global’.

Similarly lifespan extents are in practice in the eye of the beholder. Complex systems of systems such as human beings have lifespans of decades, yet systems of humans such as enterprises have typically similar lifespans.

Similarly (not) understanding information flows is a feature of the engineer not the component; a transport company is a system of components that include vehicles. Vehicles are systems of components that include engine management systems, that in turn include microchip information exchanges that are often not very well understood at all when operating in the real world, and so on. Understanding of the information exchanges varies from engineer to engineer and community to community.

The required functions too change; even if a car has been ‘optimised’ for a certain set of requirements, the uses that the owner might want to put it to changes from journey to journey and during the lifetime of ownership as the owner’s lifestyle changes.

And so on.

Is it a new thing?

This paper (A New Accident Model for Engineering Safer Systems PDF), was included as a discussion paper at a Systems of Systems Architecture (Safety) group and claims that we are dealing with new and more complicated systems as technology enables more complex systems.

Yet biological systems are some of the most complex systems that we encounter, and the primitive farmer has had to run systems of these components as a matter of course. The horse pulling a plough, for example, has to be managed as a system and yet is an essential component of some subsistance agricultural farms.

Reverse the polarity…

A system of components is supposedly ‘well understood’ and so there is a top-down view of how the components interrelate and the components are seen as discrete black boxes. It is easy to diagram and describe.

With systems of systems these components are opened up and the interrelationships are less well understood; a kind of ‘inside out’ view, where we sit within this large surrounding system, looking around at a complexity we can’t comprehend.

These are descriptions of viewpoints and the engineers’ understanding though, not descriptions of the systems themselves. As long as the terms are used as a way to categorise viewpoints then this is alright, but unfortunately the terms seem to be used to describe a ‘new’ problem, and so therefore we need ‘new’ ways of approaching it, thus discarding much of what we have learned about systems engineering.

It’s a learning thing

It may be that this is simply part of the way that we preserve corporate or community knowledge. Because expertise is hard to pass on, there is a tendency as new blood arrives to generate ‘new paradigms’ that are a small iterative improvement (hopefully) on the previous paradigm. People are essentially re-learning many existing concepts under the guise of exciting shiny new terms that provide the motivation. More later…

It’s just that I don’t understand

As long as we don’t lose sight of the fact that systems of systems are ‘just’ systems, the term can be use to indicate the engineers’ perhaps quite legitimate incomprehension of the complexity of the system under discussion.