Ultra Large Scale Systems

Ultra Large Scale Systems, York EngD programme, 2010 Slide 1
Ultra Large Scale Systems
Ian Sommerville

Objectives
• To discuss the notion of ULSS systems
• To introduce the SEI study report on ULSS

Acknowledgements
• Much of the material in this presentation has been
derived from:
• Ultra-large Scale Systems
– Linda Northrop, Software Engineering Institute, Pittsburgh
– Presented at the St Andrews Workshop on Socio-technical
Systems, September 2009.

From LSCITS to ULSS
• At around the same time as the LSCITS research and
training initiative was being considered in the UK, a
related study was underway looking at issues around
ultra large scale systems
• LSCITS: 5-10 year perspective
• ULSS: 10-20 year perspective
• ULSS study was about identifying research
requirements rather than doing research.
• Completely independent initiatives but considerable
overlap in conclusions

ULSS Report
• ULSS report, published
in 2006
• Report of a study
commissioned by US
DoD on the future of
software
• Identifies what is meant
by an ULSS
• Identifies research
areas and challenges

Societal problems
• Society is facing major problems and challenges
– Climate change
– Ageing populations in developed countries
– Feeding a growing world population
– Power for a developing world
– Safety and security
– Managing megacities
• Without doubt, these problems can only be addressed using
large and complex software systems
• However, these are ‘wicked problems’ – we cannot specify them
in detail so an evolutionary approach to systems engineering is
essential

Ultra large scale systems
• A ULS System has unprecedented scale in some of these
dimensions:
• lines of code
• amount of data stored, accessed, manipulated, and refined
• number of connections and interdependencies
• number of hardware elements
• number of computational elements
• number of system purposes and user perception of these purposes
• number of routine processes, interactions, and “emergent behaviors”
• number of (overlapping) policy domains and enforceable mechanisms
• number of people involved in some way

ULSS
• ULS systems will be interdependent webs of software-
intensive systems, people, policies, cultures, and
economics.
• ULS systems are systems of systems at internet scale
• The boundary between a ULSS and an LSCITS is a very
blurred one. In some cases, it may be appropriate to
think of these terms as synonymous but the general
implication in the report is that ULSS have all of the
characteristics of an LSCITS but at an even larger
scale
– The purpose of an ULSS is typically broader than that of an
LSCITS and a ULSS will normally include many LSCITS

Do ULSS exist?
• My reading of the report is that it envisages a ULSS as
a web of interconnected automated systems. The
ULSS report assumes that these systems do not yet
exist.
• However, what about:
– The World Wide Web
– International air traffic control
– Portfolio of applications in a major multinational company
across several continents

ULSS and SoS
• Purpose vs Opportunism
– SoS are integrated and built to fulfil specific purposes
– ULSS have no single well-defined purpose (although they
may be created to support from broad goal such as safe air
traffic management or intercontinental power management).
From ULSS, more specific systems are created to tackle
individual problems
• Centralisation vs Decentralisation
– SoS have a single centralised authority and an agreed
purpose e.g. the Navy are the authority for SoS on a warship
– ULSS have no centralised authority and no agreement
amongst stakeholders on the purpose of the system

Scale changes everything
• Characteristics of ULS systems arise because of their scale.
– Decentralization
– Inherently conflicting, unknowable, and diverse requirements
– Continuous evolution and deployment
– Heterogeneous, inconsistent, and changing elements
– Erosion of the people/system boundary
– Normal failures
– New paradigms for acquisition and policy
• These characteristics may appear in today’s systems and systems
of systems, but in ULS systems they dominate.
• These characteristics undermine the assumptions that underlie
today’ssoftware engineering approaches.

Today’s approaches
• The Engineering Perspective - for large scale software-intensive systems
• largely top-down and plan-driven
• requirements/design/build cycle with standard well-defined processes
• centrally controlled implementation and deployment
• inherent validation and verification
• The Agile Perspective - proven for smaller software projects
• fast cycle/frequent delivery/test driven
• simple designs embracing future change and refactoring
• small teams and retrospective to enable team learning
• tacit knowledge
• Today’s approaches are based on perspectives that fundamentally do not cope with the new
characteristics arising from ultra-large scale.
• The mentality of looking backward doesn’t scale.

Systems as buildings

ULSS as cities

Are ULSS like cities?
• Cities (in developed countries) are controlled entities
– There is an elected local city government that is responsible
for coordinating work on utilities, managing disruption to
citizens, approving plans for development, etc.
– Cities only work successfully because of this local
government – they have not just evolved.
– Without this central control, cities were dangerous places
with high crime levels, dangerous buildings, uncontrolled
development, high levels of disease and poverty, etc.
• Who will play the role of the ‘city council’ for ULSS?
• Will the lack of such a role hinder the development of
ULSS?

Socio-technical ecosystems
• Socio-technical ecosystems include
– People, organizations, and technologies
at all levels with significant and often
competing interdependencies.
– There will be competition for resources.
– There will be organizations and
participants responsible for setting
policies.
– There will be organizations and
participants responsible for producing
ULS systems.
– There will need to be local and global
indicators of health that will trigger
necessary changes in policies and in
element and system behavior.

Central challenges of ULSS
• Design and evolution
• Orchestration
• Monitoring and assessment
• Organizational integration
• Regulation and control

Design and Evolution
• Specific challenges in ULS system design and evolution stemming
directly from the characteristics of ULS systems:
– Economics and industry structure
– Social activity for constructing computational environments
– Legal issues
– Enforcement mechanisms and processes
– Definition of common services supporting the ULS system
– Rules and regulations
– Agility
– Handling of change
– Integration
– User-controlled evolution
– Computer-supported evolution
– Adaptable structure
– Emergent quality

Orchestration and control
• Orchestration and control refers to the set of
activities needed to make the elements of a ULS
system work together in reasonable harmony to
ensure continuous satisfaction of mission objectives.
• Orchestration is needed at all levels of ULS systems
and challenges us to create new ways for
– Online modification
– Maintenance of quality of service while providing necessary
flexibility
– Creation and execution of policies and rules
– Adaptation to users and contexts
– Enabling of user-controlled orchestration

Monitoring and assessment
• The effectiveness of ULS system design, operation,
evolution, orchestration, and control has to be
evaluated.
• There must be an ability to monitor and assess ULS
system state, behavior, and overall health and well
being.
• Challenges include
– Defining indicators
– Understanding why indicators change
– Prioritizing the indicators
– Handling change and imperfect information
– Gauging the human elements

Reductionist view of research

Post-reductionist research

ULSS research areas
• Human interaction
• Computational emergence
• Design
• Computational engineering
• Adaptive system infrastructure
• Adaptable and predictable system quality
• Policy, acquisition and management

Conclusions
• There is an unstoppable trend toward increasing scale in many
systems important to our society.
• Scale changes everything. Manifestations of scale and its
attendant complexity arise in many disciplines, and can be
understood as a phenomenon in its own right.
• New, interdisciplinary perspective and new research in building
ultra large-scale systems is long overdue.
• “Since computation has moved over the past twenty years
decisively closer to people, interfaces with social sciences such
as Psychology and Sociology, besides Economics, have become
increasingly important”
– Christos H. Padadimitriou, in “Algorithms, Games, and the Internet”

Conclusions
• What you call a system (system of systems, ULS
system, complex net-centric system, LSCITS) is really
unimportant.
• It is important that ULS system characteristics are
recognized.
– These characteristics undermine the assumptions we make in
most current technical, management, and acquisition
approaches.
– The ULS system perspective is helpful in understanding some
of the current technology and management shortcomings
and issues with system of systems.

Ultra Large Scale Systems

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