Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-1

Beyond the Design Stance- losing some control but gaining some

adaptivity

Bruce Edmonds (including some results of David Hales)

Centre for Policy Modelling

Manchester Metropolitan University Business School

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-2

Some thoughts on: limitations of the design stance applied to messy and complex systems

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-3

The primary systems aim

• That the system should work well in practice once deployed in its operating context

• One way of trying to achieve this aim is, what I call the (strict) design stance:

1. That the system should work according to its specification

2. and that the specification should be designed to achieve its design goals

3. and that its goals are the appropriate ones.

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-4

Some (well known) causes of problems with the design stance

• Context of operation is (at least partially) unknown to designers

• Good in practice operation requires meaningful, complex and abstract goals,

• Thus, either one has a:High-level specification, in which case you can’t

guarantee that the system works according to its specification

Or a Low-level specifiction in which case you can’t guarantee that the specification achieves the goals

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-5

Some (well known) syptoms caused by the design stance

• Systems with inappropriate goals for the context of operation

• Systems that are difficult to adapt to new contexts of operation

• Brittle systems (i.e. ones that don’t work after minor change in use)

• Systems that are not under the control of the system users

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-6

Some (well known) remedies to these problems

• Abstraction• Automation• Standardisation• Modularity• Formalisation• Transparency• Redundancy• Adaptivity• Testing

Engineered Agent Approach

Beliefs, intentions, etc.

Automatic verification

Ontologies, protocols

Agents, groups, teams

Logics

Complex Systems Approach

Actor

Simulation

Agents, groups, societies

Social&biological analogies

Duplication, competition

Social&individual learning

Post hoc exploration

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-7

Some kinds of complexity

• Syntactic Complexity– When the computational ‘distance’ between

initial conditions and outcomes is too great to be analytically bridgable

There are different views of a system

• Semantic Complexity– When any formal representation is necessarily

incomplete Models are context-dependent You probably need many of them

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-8

Inseperable system embedding

When the computer system is embedded into a wider system such that

the wider system can not be seperacted from the computer system to aid analysis

without changing the behaviour of both computer system and the wider system,

then off-line analysis and design is usually difficult and ineffective.

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-9

What if the properties of MAS are more like Biology than Physics?

• Lots of kinds of agents, teams, trust, communication forms, etc.

• Lots of observation and exploration before any abstraction into theory possible

• A priori foundationalist studies based on plausibility probably worse than useless

• Success defined by: what works in context, redundancy, and adaptability

• Not by abstraction, modularity and analysis

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-10

Using science

• Theory developed empirically (not a priori)

• Can only be applied using well-validated processes and tools

• How the theory can be applied using what approximations empirically established

• The conditions when theory can be safely applied learnt with practice

• Properties can only be deduced (given the above) after theory has been validated

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-11

E.g. Engineering a bridge

• Use of well-validated general designs (e.g. arches, columns, suspension)

• Multiple approximate calculations (maximum stress, weight, compression)

• Use of well-validated components or components made using well-validated techniques (e.g. standard girders or cable)

• Simulations of the set-up (e.g. oscillations)

…still the unexpected may occur - no illusion that prior proof can be relied upon.

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-12

Some practical steps towards understanding MAS

• Capturing MAS in simulations• Exploring the different dynamics• Observing MAS in practice• Trying out MAS organisational mechanisms• Postulation theories about MAS• Checking theories using experiments• Testing predictions about MAS using these

theories• Learning the limitations of the theories and

how to apply them

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-13

Why so much commitment to a pure design stance?

Some guesses:• Illusion that computational systems are

deterministic at macro level in practice because they are in theory at micro level

• Blame is contained to system production from specification, and substantially defrayed to user from designer

• Fixed goals suit management, external consultants and academics

• Used to dealing with simple systems

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-14

An Example: Using ‘tags’ to help with distributed lorry loading

(Hales and Edmonds 2002)

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-15

The distributed lorry loadingproblem

• Problem from Kalenka and Jennings (1999)

• 10 loading bays where lorries (size s) may randomly arrive if the bay is empty (prob p) to be unloaded (they go once empty)

• Set of 5 robots ‘assigned’ to each bay

• Robots can unload 1 unit per time cycle

• Robots can decide to help at other bays

• Efficiency judged by percentage of robots who are idle over a long time

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-16

Designed social rationality

• Social Rationality (Hogg and Jennings)– If a socially rational agent can perform an

action whose joint benefit is greater than its joint loss, then it may select that action.

• Ask for help if have a lorry to unload

• Two standard strategies for responding to request:– Selfish: never help (only unload own bay)– Social: unload own but if idle help requester

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-17

Tag mechanism

• Each robot has: T [1..500], L [0/1], N [0/1]

• If have lorry ask robot with same T otherwise a random robot

• Asked robot uses state and L, N for action

• Triples probabilistically propogated to other robots in proportion to amount unloaded in own bay (some mutation of T, L, N)

• If not helping another and has lorry unload

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-18

3 Test loading scenarios

• When p is high and s is low then jobs are arriving at a smother constant rate

1. p = 0.25, s = 100

2. p = 0.05, s = 400

3. p = 0.01, s = 1000

• When p is small but s is large then deliveries are more sporadic, with lots of help required in bursts

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-19

Preliminary results

20

25

30

35

40

p=0.25, s=100 p=0.05, s=400 p=0.01, s=1000

Loading Scenario

Ro

bo

ts I

dle

%

selfish social tag

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-20

Tag based methods

• Groups of identically tagged controllers learn to aid others in the group with no explicit contract or central enforcement

• Defectors can arise to exploit such a group, but this quickly kills the group it is in

• Groups dynamically arise and dissolve all the time, adapting to load and defectors

• Tag based group-formation seems reasonably robust

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-21

Dynamic group formation via tags (David Hales 1999)

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-22

Scalability of tag cooperation, (David Hales 1999)

0 2000 4000 6000 8000 10000 12000 14000

100

200

400

800

1600

Nu

mb

er

of

ag

en

ts (

N)

Generations before co-operation

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-23

Summary of lorry loading example

• Results in this simulation follow those in many other simulations using tags

• Tags are an example of an apparently robust and reliable system of decentralised adaption and cooperative group formation

• Cooperation is not certain but highly likely• Properties and conditions of applicability of

the technique can be found experimentally• It is an example of decentralised adativity

and effectiveness from validated technique

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-24

Conclusion of talk

• Suggested a move away from a foundationalist approach towards a more empiricist approach…

• with less emphasis on prior verification and more on post hoc validation…

• where reliability comes from experimentally tested theories of system behaviour…

• (formalisation only entering based on such theory)• which entails a loss of theoretical certainty…• but offers greater potential for adaption and in

practice performance.

Beyond the design stance, AgentLink MSEA/ABSS SIG meeting, Barcelona 2003, http://cfpm.org/~bruce slide-25

The End

Bruce Edmonds

bruce.edmonds.name

Centre for Policy Modelling

cfpm.org