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Networks are the true structure to complex engineered systems and in this section, we discuss the importance of seeing these systems from the perspective of access, connectivity, and networks.



Transcription:

Complex systems are by many definitions highly interconnect, examples being social networks, financial networks and transportation networks. In these highly interconnected systems, it is increasingly the connections that define the system as opposed to the properties of their constituent components. This is quite an abstract concept so some examples might help us to grasp it.
Think of the expression “it is not what you know but who you know”. It would be more accurate to say, in an isolation system it is what you know that matters, but in an interconnected system it is increasingly who you know that matters, that is the connections that you have.
Another more concrete example might help to illustrate this important concept better, think of an expensive sports car, out on the highway it is king doing 0-60 in under three seconds and up to 250 kilometres an hour, these properties of the car are admittedly pretty cool, but put this car in urban traffic and it will be gridlocked like any other car no matter how great the properties of the car it will only be going as fast as the transportation network allows it.
This should demonstrates that in these complex systems it is the structure and dynamics of the network that really matter, it is not about being bigger, faster or stronger it is about access and access is defined by where you lie in the network and the structure of that network.
Think of the air transportation system, it is not so much the static properties of your location in space and how far away your destination is, but more importantly where you are located in the network, if you are beside a major hub it can be quicker and easier to travel to another major hub on the other side of the planet as it would be to travel from one disconnect hub to another that is a fraction of a the distance away.
So hopefully these examples illustrate to you the importance of seeing these complex engineered systems from the perspective of connectivity and networks as opposed to seeing them as things, irrespective of whether we explicitly call them networks or just systems, networks are the true geometry behind complex systems and thus it is very important to think about designing them from this perspective of access, connectivity and network structure.
In order to do this we first need to understand a bit about the nature of networks, and network theory is the area of math and science that provides us with the models for analysing networks, so lets take a look at some of the key features to networks and how they will effect the system as a whole.
Probably the most important feature to a network is its degree of connectivity, that is how connected is the whole system? Designing for a densely populated urban environment like Hong Kong will be very different to designing for a city like Los Angela which is dispersed. In highly interconnect systems the dense interconnections can require much greater layering, the components can be much more specialised and there may be a much higher level of dependencies.
As a result of this failures can quickly propagate, a small security scare in one airport for example can result in delays across large areas of the air transportation system within a nation.
In these large, highly interconnected system we don’t always know the dependencies, no one has complete knowledge of all the interlinkages that regulate complex systems like large urban centres or our global supply chain.
Thus our aim should not be to design these systems to be perfect, 100% fault tolerant, this is not realistic, instead they need to be engineered so as to be robust to failure, the internet again is a good example of this, it is what is called a “best effort network” this means it tries its best, but if something goes wrong, then it is no big problem it just drops your packet and tries again, it
happens all the time but the internet still works, the occurrence of failure should be designed into these systems and not out of them in order to achieve robustness.
Another key consideration in the design of these networked systems is their degree of centralisation verse decentralisation, as this is a defining factor in the structure and makeup to networks. In centralised networks we have a node or small set of nodes that have a strong influence on the system and the network will be largely defined by the properties of these primary nodes.
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