Consistency Check in
Modelling Multi-Agent Systems
Lijun Shan
Hong Zhu
Dept of Computer Science
National Univ.of Defense Tech.
Changsha, 410073, China
[email protected]
Dept of Computing
Oxford Brookes Univ.
Oxford OX33 1HX, England
[email protected]
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Outline
Motivation and related work
Agent-oriented software development (AOSD)
Model-driven software development (MDSD)
Roles and problems of consistency checking in MDSD
Definition of consistency constraints
Consistency checkers in a modelling environment
Case studies
Conclusion
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Motivation
Agent technology:
Widely recognized as a viable solution for
applications in dynamic environments such as the
Internet
Agent-oriented methodologies, such as Gaia,
Tropos, AUML, etc.
CAMLE: Caste-centric Agent-oriented Modelling
Language and Environment
as a method of requirements analysis and specification
as the base for the design and implementation of MAS
to generate formal specifications in SLABS
to write programs in AO programming languages
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Model-driven SW development
Models play the central role in SW development
modelling real world systems
as a means of requirements analysis
modelling software/information systems
as specifications of software systems
to analyse system’s properties, etc.
as high level designs
to derive or generate code
even as executable representation of software systems
as bases of software testing, etc.
Characteristics of modern modelling languages
Semiformal diagrammatic notation with defined semantics
Facilities to support separation of concerns
Multiple views
Hierarchically structured collection of diagrams
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Consistency as a basic quality attribute
Consistency:
Between different views
Between models at different levels of abstraction
Consistency is crucial in MDSD
A model must be consistent before it is transformed into
other forms, e.g.
the generation of code,
the derivation of test cases,
the uses as software documentation,
A model must be consistent before the derivation and
proof of the properties of the system
Ensuring consistency is very difficult
Related to the semantics of the model
Complexity due to multiple views and multiple levels
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Consistency check: a challenging problem
The aim of consistency check is to provide a partial
but effective solution to model consistency problem.
Defining a set of consistent constraints that can detect a
large number of common errors in models
Design algorithms that can automatically check if a model
satisfies the consistency constraints
The idea of consistency check in modeling languages is
similar to type check in programming languages:
 defining a type system to prevent type errors
 device a static type checking mechanism
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Consistency constraints
What are consistent constraints?
Restrictions on the uses of diagrammatic notations,
variables and names, types and symbols in a modeling
language to reduce the possibility of inconsistency
Related to the semantics of the diagrams
Must be able to be syntactically checked
Typical examples
The same identifier that occurs at different places must
refer to the same entity
An entity should be referred to by the same identifier if
it occurs at different diagrams
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Types of consistency constraints
Intra-model consistency:
Within one type of model
Intra-diagram:
Within one diagram
Inter-diagram:
Between models/diagrams
of the same level of
abstraction
Vertical consistency:
Between different
diagrams of the same
model
Inter-model consistency:
Between different types
of models, hence also
different diagrams
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Horizontal consistency:
Between models/diagrams
at different levels of
abstraction
Local:
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Between two levels
Global:
With respect to the overall
structure
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Related work
Defining consistency constraints for UML:
(Andr´e, P. 2000), (Pap, Z. S. 2001), (Nentwich, C. 2001),
(Paige, R. F. 2002), (Astesiano, E. 2003)
Generic tools
Xlinkit: language for defining consistency + engine for
automated checking, (Nentwich, C., Emmerich, W., &
Finkelstein, 2003)
Formal methods (e.g. SPIN)
(Inverardi, P. 2001), (Schafer, T. 2001)
As a part of modelling environment
NDRASS (structured modelling) (Xu, J., Jin, L., & Zhu, H.
1996)
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Overview of CAMLE
Conceptual model of multi-agent systems
[2]
Agent:
an active computational entity that encapsulates data,
operations and behaviours and situates in its designated
environment
state space
a set of operations/actions
designated operating environment
a set of behaviour rules
Caste:
a set of agents that have the same structural and
behavioural characteristics
agents are instances of, but have dynamic memberships of castes
inheritance relationship between caste
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Overall Structure of CAMLE Models
Collaboration Models and Behavior models
A CAMLE model consists of
• a caste model
• collaboration models
• behaviour models
Caste Model with Whole-Part Relations
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Caste model
Caste model
models the
organizational
structure
Notation
Example
Caste diagram
Defines the
castes in the
system
Specifies their
relations
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Constraints on Caste Model
Constraint 1a) A caste diagram defines a naming space in
which each node defines a caste with a unique name.
Constraint 1b) Each link defines a binary relation on castes
by linking two nodes in the diagram.
Constraint 1c) An inheritance relation and a migration
relation must be associated to two different caste nodes.
Constraint 1d) Inheritance relations must not form any
loops.
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Collaboration models
Collaboration Diagram
Describes the dynamics of a system from communication
perspective
The structure of collaboration models
A hierarchic of collaboration models as refinement of castes
A collaboration model for each compound caste:
a general collaboration diagram + a set of scenarios specific
collaboration diagrams
Notation
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Example
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Constraints on Collaboration Model
Well-formedness conditions
Constraint 2a) Each caste / agent node must have a unique name.
Constraint 2b) The number assigned to an action indicating its
temporal order must be unique, if any.
Consistency between general and specific diagrams, e.g.
Constraint 2c) Every agent node in the general collaboration
diagram G must appear in at least one scenario-specific
collaboration diagram. Formally,
nANode (G).DS. (nANode (D))
Consistency between models at different levels, e.g.
Constraint 2j) For all castes C in a collaboration model M, C’s
environment described in M must be equal to C’s environment
described in C’s collaboration model MC.
n.(nEnv(MC)  aInteraction(G).(n=Begin(a)C =End(a)))
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Behaviour models
Scenario diagram
Describes a typical
situation in the operation
of a system from an
agent’s view.
used in behaviour
diagrams
behaviour diagram
define behaviour rules of
an agent
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Constraints on Behaviour Model
Well-formedness conditions, e.g.
Constraint 3a) The temporal order between events must
be linear
Consistency between behaviour diagrams and
scenario diagrams, e.g.
Constraint 3d) In a behaviour diagram, every scenario
reference node must refer to a scenario defined by a
scenario diagram.
n ScenarioNode(DC). S SC.(Name(n)=Name(S)
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Inter-Model Consistency
Between collaboration model and caste model
Constraint 4a) Every caste in a collaboration model CD must be a
caste in the caste model C. Formally,
DCD.nNode(D).n’Node(C).(CName(n)=Name(n’))
Constraint 4b) The hierarchical structure of the collaboration
models must be consistent with the whole-part relations
between castes defined in caste diagram C.
MA,MBCM.(MB < MAR Aggr(C).(R(B,A))
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Between behaviour model and caste model
Constraint 4c) For each behaviour model BM, the caste that BM
defines its behaviour must be in declared in the caste model C.
BBM.nNode(C).(Caste(B)= n ).
Constraint 4d) Every agent occurs in a scenario in a behaviour model
BM must have its caste defined in the caste model C.
BBM.aAgents(B).nNode(C).
(Caste-of(a)=Name(n))
Constraint 4e) The ‘join’, ‘quit’ and ‘move’ actions occur in the
behaviour model of a caste c must be consistent with the
migration relation described in the caste model.
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Between collaboration model and behaviour model
Constraint 4f) Every visible action of caste C defined in the
collaboration model CM must occur in C’s behaviour model BMC or
at least one of C’s components as a result action.
aVisibleActions(C).(rRules(BC) (MComponents(C).
r Rules(BM)). (a=Action(r))
Constraint 4g) For each scenario used in the definition of caste C’s
behaviour, the agents and/or castes that the scenario referred to must
occur in the collaboration model CM as C’s collaborators.
ScScenarios(BC).GRef(Sc).GCollaborators(C)
Constraint 4h) The agents/castes referred to in a scenario must be in
the environment of the caste as described by the collaboration model.
ScScenarios(B).GRef(Sc).(GEnv(C))
Constraint 4i) Every action that a scenario refers to in a behaviour
diagram must be a visible action of the caste of the scenario.
Sc Scenarios(BC).a ReferredActions(C, Sc).
(aVisibleActions(C)).
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Summary
Horizontal
Consistency
Intramodel
Local
Intradiagram
1a, 1b, 1c, 1d, 1e,
2a, 2b, 3a, 3b, 3c
Interdiagram
2c, 2d, 2e, 2f, 2g,
2h, 2i, 3d
2j, 2k
4f, 4g, 4h, 4i
4e
Inter-model
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Vertical Consistency
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Global
4a, 4b, 4c, 4d
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Consistency check tools in CAMLE
Well-formedness conditions are checked during
model construction in the process of interactive
diagram editing
Other consistency constraints are checked by a set
of tools; each for one specific constraint
Consistency checking tools are called in the
following order to reduce the complexity of error
handling:
Intra-model intra-diagram consistency checkers
Intra-model inter-diagram consistency checkers
Inter-model local consistency checkers
Inter-model global consistency checkers
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Architecture of CAMLE Environment
Users’
Requirements
Formal
Specifications
Graphic User
Interface
Specification
Generator
Model
Manager
Diagram
Editor
Partial
Diagram
Generator
Wellformedness
Checker
Consistency
Checker
Controller
Behaviour/
Collaboration
Checker
Caste/
Collaboration
Checker
Behaviour
Model
Checker
Collaboration
Model Checker
General/
Specific
Checker
Caste/
Behaviour
Checker
Cross level
Checker
Graphic
Models
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Result
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Case studies
United Nations’ Security Council:
the organisational structure and the working procedure to
pass resolutions
Amalthaea:
an evolutionary multi-agent system developed at MIT’s
Media Lab for retrieving information from the Internet
University:
a partial model of the university organisation and working
procedures
Web Services:
a model of the architecture of web services and an
application of web services of online auctions
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Observations on case studies
In all cases, automated consistency check detected a large
number of errors
Models that passed consistency checks are of good
quality
Explicitly defined consistency constraints helped modeler
to think more carefully in the construction of models,
hence made fewer mistakes during modeling than without
constraints
The design and implementation of the transformer for
generating formal specifications become much simpler
with the assumption that certain inconsistency can be
ruled out
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Conclusion
Roles of consistency constraints in MDSD
Quality assurance in modelling process
Consistency constraints can be defined to effectively improve
the quality of models and the productivity in model construction
Consistency checking can be implemented efficiently as a very
useful tool in a modeling environment
Partial specification of the correctness of the
transformation rules between models
The diagram generators in CAMLE can guarantee that a
generated model (or partial model) is consistent with the
original diagram(s).
Further work
Statistical analysis of the effectiveness of consistency
constraints
Further development of CAMLE environment
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References
1. Shan, L. & Zhu, H. CAMLE: A Caste-Centric Agent Modelling Language
2.
3.
4.
5.
and Environment. Proc. of SELMAS at ICSE’04, Edinburgh, Scotland (UK),
May 2004.
Zhu, H. SLABS: A Formal Specification Language for Agent-Based
Systems, Journal of Software Engineering and Knowledge Engineering
11(5), 529-558, 2001.
Pap, Z. S., Majzikl, I., Pataricza, A, & Szegi, A. Completeness and
Consistency Analysis of UML Statechart Specifications. Proc. of IEEE
Design and Diagnostics of Electronic Circuits and Systems Workshop, 8390. 2001.
Nentwich, C., Emmerich, W., & Finkelstein, A. Flexible Consistency Check.
ACM Transactions on Software Engineering and Methodology 12 (1), 2863, 2003.
Inverardi, P., Muccini, H., Pelliccione, P. Automated check of architectural
models consistency using SPIN. Proc. of 16th IEEE Int. Conf. on
Automated Software Engineering, San Diego, California, p.346, 2001.
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