Engineering systems with emergent behaviour Graeme Smith The University of Queensland Australia

Draft Research Agenda Specification and Design – “Abstractions and models for massively parallel, open-ended systems. We currently lack the necessary abstractions and foundations to describe, model, and design massively parallel systems …”

Draft Research Agenda Specification and Design – “Deducing a global specification from local rules, and finding local rules that produce a desired global behaviour. … we will have to integrate services as parts into a larger environment. We will thus no longer be able to use a top-down approach …” – addresses deployment – BUT not system development

Is top-down development possible? According to the literature, top-down development of emergent behaviour is either: 1. Impossible 2. Impracticable 3. Difficult But which?

Impossible By definition By analogy with emergence in natural systems By Gödel's incompleteness theorem Because it is an undecidable problem (?) Because it requires high and low level languages

Impracticable As an accepted fact By analogy with emergence in natural systems However – Smale and Cucker (2005) behaviour of individual birds  flocking – Zhu (2005) autonomous sorting

Topics of interest Categorisation and formalisation of emergent properties (macro level) – statistical distribution, convergence, stability,… Modelling of intelligent, adaptive components (micro level) – goals, model of environment, … Coordination of components (meso level) – interaction patterns, mediating infrastructure (inspiration from biology, physics, society)

Strategies for the meso level Scenarios (cf. Zhu, engineering emergence) Abstract mediators (cf. Hayes, deadline command) Time scales (cf. Burns, time bands) Islands of interaction (cf. Hogg, aliasing control) … Key is incremental development.

Example: shape-forming atoms L1: all atoms are in a position of desired shape L2: a subset of the atoms that are not in position, move into a position of desired shape (all atoms already in a position do not move) L3: an atom not in the desired shape moves next to one in the desired shape that needs a neighbour (initially at least one atom is in the desired shape)

Example continued L4: an atom in the desired shape broadcasts its need for a neighbour (atoms in position store a model of the desired shape) an atom not in the desired shape responds to broadcast by moving to broadcaster L5: a message is broadcasted by moving between neighbouring atoms which increment a number it carries. This number is stored by the receiving atom and hence creates a gradient which can be followed to the broadcaster

Revised Research Agenda Specification and Design – “Deducing a global specification from local rules. Influencing the global behaviour by making local changes. … we will have to integrate services as parts into a larger environment. We will thus no longer be able to use a top-down approach …”

Revised Research Agenda Specification and Design – “Finding local rules that produce a desired global behaviour. To guarantee the presence of desired global behaviour, and the absence of undesired global behaviour, new top-down development approaches are needed. Such approaches must deal with the massive scale and complex interactions of ensembles.”