System of systems

System: a collection of components organized to accomplish a specific function or set of functions (IEEE)

System-of-Systems: “a set or arrangement of systems that results when independent and useful systems are integrated into a larger system that delivers unique capabilities” [DoDDef. Acq. Guidebook 2004]

Emergent behavior, Evolutionary Development, Operational Independence of the Elements, Managerial Independence of the Elements, Geographic Distribution [Maier1996]

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System of Systems – Intuitive sense

Intuitive sense of meaning of systems of systems An arrangement of systems that enables achievement

of a bigger and more interesting function than cannot be achieved by any of the component systems alone

This is insufficiently sophisticated to enable meaningful discussion of systems of systems design methods

I provide illustrations to enable thinking about the issues

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Systems of Systems (example 1)

Prime system 1

Prime system 4

Prime system 3

Prime system 2

AirportMany systems arranged to give meaning, purpose and effectiveness to each systemDesign of each complements the others – deliberate development of emergence

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Traffic in a well ordered system Users adhere to rules

of use Infrastructure design

complements Rules of use Density of users

Outcome is orderly traffic

System of Systems (example 2)

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System of Systems (example 3)

Traffic in a poorly ordered system Users do not adhere to rules of use Design does not match actual use patterns

Outcome – 10 lane car park with 60mph limit!Superficially similar to example 2

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System of Systems (example 3)

Traffic in a poorly ordered system Users do not adhere to rules of use Design does not match actual use patterns

Outcome – 10 lane car park with 60mph limit!Superficially similar to example 2

The cause ofthe trouble

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System of Systems (example 4)

Military expeditionary force Army personnel and equipment delivered to a site by Navy ship, all supported by Air Force assets providing transport, support and

surveillanceAssets not specifically designed to support each

other But within one nation it is reasonable to expect (at time of

acquisition) that they may need to inter-operateCoalition of nations

Not reasonable at time of acquisition to expect inter-operation Potential issues of secrecy preventing design for

interoperability – so the coalition is ‘come as you are’

So … What is A System of Systems?

A A System of Systems (SoS) System of Systems (SoS) is a “super-system” made up of is a “super-system” made up of elements – each of which is itself a complex, independent elements – each of which is itself a complex, independent system -- that interact to achieve a common goal.system -- that interact to achieve a common goal.

-- Are These SoS? --

Major League Baseball

• SoS elements (i.e., the systems) can and do operate independently.• An SoS evolves – functions are added/removed/changed with experience.• An SoS exhibits emergent behavior not attributable to any element (system).• An SoS is geographically distributed – elements exchange information only.

International Air TravelJoint Theater Ops

Hardware

From INCOSE

Source: Monica Farah-Stapleton, IEEE SOS conference, 2006

Army SOS Perception

Emergence

EmergenceMacro level behaviors (patterns) that cannot be predicted from studying the micro level behaviors in isolation

Or the Whole is greater than the sum

Complex Systems of Systems composed of a (1) large number of entities, with (2) non-trivial interaction networks (not too simple or too complete) , whose (3) impacts on one another are non-linear, and whose overall behavior tends to display emergent characteristics

Characteristics of Emergence

• System-level properties exist only at the system level as it functions, beingdifferent from and existing beyond the constituent element, or subsystem,properties.

• System-level properties are not held by any of the isolated elements.

• System-level properties are irreducible. They simply cannot be understood, explained, or inferred from the structure or behavior of constituent elements or their local properties.

• Understanding cause–effect relationships can only be established throughretrospective interpretation. This renders traditional reduction-based analytic techniques incapable of useful predictions of emergent system-level behavior.

Principles of emergence

• Condition of Emergence An avalanche condition, or a critical state, has to

exist prior to the occurrence of emergence.• Emergent behavior is inversely proportional

to the degree of bondage between systems– The more tightly the component systems are coupled

the less likely that the global emergent behavior willprevail.

– Emergent behaviors do not arise in closed hierarchically

structured systems.

Principles of Emergence (2)

• Emergent behavior is non-linear– Emergent behavior is more than the sum of added component systems.

– the output is not proportional to the inputs.• Emergent behavior is self-organized – Self-organization is a process in which the internal

organization of a system, normally an open system, increases in complexity without being guided or managed by an outside source.– This is a bottom-up process.

Examples of Emergence From Nature

• Crickets tend to synchronize their mating calls - calling all at once at the same speed.

Seasonal birds fly in large groups that seem to behave as one.

• The individual ants do not know about coordinated foraging; the hive as a whole knows.

consciousness is an emergent property of brains.

Computing Examples

Router Synchronization Router periodically exchange protocol messages in huge

amount Floyd and Jacobson showed that in a network with “many

apparently independent periodic processes ... these processes can inadvertently become synchronized”

The process is abrupt and large random components were needed to avoid synchronization

Ethernet capture effect If A and B simultanously send packets collision will occur,

Suppose that A chooses a smaller back off than B. A always win because it reset timer and send and B get Worse little extra delay was needed to insert to win

Misconfigured Load Balancer

multi-tiered distributed application, with numerous clients

Load balancer spread the load evenly and also detect the failure of App server

At some point, the system stops responding to requests.

the application servers are no longer responding to the load balancer within its configured timeout, and the load balancer ends up declaring both application servers dead.

one could argue that someone chose the wrong timeout for the load balancer, but that error might not have been obvious when the system was first tested

Internet Protocol

No IP router knows the complete topology of interconnections for the Internet or even the configuration of local interconnections in its own neighborhood

Configuration on router and bandwidth changes continuously Still IP is reliable and efficient Each IP router along the path of a message decides which of

its immediate neighbor routers will constitute the next hop without knowledge of routers or likely paths beyond that immediate neighbor

IP routing emerges as reliable despite of incomplete, imprecise, and outdated information;

What is not Emergence

Single-component bugs that break the whole system• When critical part of system stop working

• Inherently inefficient algorithms Replicated file system that contacts replicas serially rather than in

parallel will likely have sub-optimal performance.Insufficient resources: CPU, memory, network latency and bandwidth, storage capacity,

latency, and bandwidth

Some research Questions

1.What is different about the nature of the SoS problem domain in contrast to more traditional problem domains?

2. How do philosophical, methodological, and axiomatic perspectives influence effectiveness in dealing with emergence in the SoS problem domain?

3. Given that emergence is going to occur in SoS, what are the implications for designing methodologies (approaches) that will enhance effectiveness in dealing with emergence?

4. What are the primary considerations that a designer of SoS should think about with respect to effectively dealing with emergence?

5. How might we assess the degree to which emergence is going to be problematic in an SoS effort?

6. What guidance for emergence might we give an engineering team getting ready to engage in an SoS problem?