consistency check in modelling multi-agent systems

Sept. 2004 COMPSAC'2004 1

Consistency Check in Modelling Multi-Agent Systems

Lijun Shan Hong ZhuDept of Computer Science Dept of Computing

National Univ.of Defense Tech. Oxford Brookes Univ.

Changsha, 410073, China Oxford OX33 1HX, England

[email protected] [email protected]


OutlineMotivation 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 environmentCase studiesConclusion


MotivationAgent 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


Model-driven SW developmentModels play the central role in SW development

modelling real world systems as a means of requirements analysis

modelling software/information systemsas specifications of software systems

to analyse system’s properties, etc. as high level designs

to derive or generate codeeven as executable representation of software systemsas bases of software testing, etc.

Characteristics of modern modelling languagesSemiformal diagrammatic notation with defined semanticsFacilities to support separation of concerns

Multiple viewsHierarchically structured collection of diagrams


Consistency as a basic quality attributeConsistency:

Between different views Between models at different levels of abstraction

Consistency is crucial in MDSDA 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 difficultRelated to the semantics of the modelComplexity due to multiple views and multiple levels


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 errorsdevice a static type checking mechanism


Consistency constraintsWhat 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 diagramsMust be able to be syntactically checked

Typical examplesThe 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


Types of consistency constraints

Intra-model consistency: Within one type of model

Intra-diagram: Within one diagram

Inter-diagram: Between different diagrams of the same model

Inter-model consistency:

Between different types of models, hence also different diagrams

Horizontal consistency: Between models/diagrams of the same level of abstraction

Vertical consistency: Between models/diagrams at different levels of abstraction Local:

Between two levels Global:

With respect to the overall structure


Related workDefining consistency constraints for UML:

(Andr´e, P. 2000), (Pap, Z. S. 2001), (Nentwich, C. 2001), (Paige, R. F. 2002), (Astesiano, E. 2003)

Generic toolsXlinkit: 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 environmentNDRASS (structured modelling) (Xu, J., Jin, L., & Zhu, H. 1996)


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 spacea set of operations/actionsdesignated operating environmenta 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 castesinheritance relationship between caste


Overall Structure of CAMLE Models

Caste Model with Whole-Part Relations

Collaboration Models and Behavior modelsA CAMLE model consists of

• a caste model• collaboration models• behaviour models


Caste modelCaste model

models the organizational structure

Caste diagram

Defines the castes in the system

Specifies their relations

Notation Example


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.


Collaboration models

Collaboration Diagram Describes the dynamics of a system from communication perspectiveThe structure of collaboration models

A hierarchic of collaboration models as refinement of castesA collaboration model for each compound caste:

a general collaboration diagram + a set of scenarios specific collaboration diagrams

Notation Example


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 te

mporal order must be unique, if any. Consistency between general and specific diagrams, e.g.Constraint 2c) Every agent node in the general collaboration diagr

am G must appear in at least one scenario-specific collaboration diagram. Formally,

nANode (G).DS. (nANode (D))Consistency between models at different levels, e.g. Constraint 2j) For all castes C in a collaboration model M, C’s en

vironment described in M must be equal to C’s environment described in C’s collaboration model MC.

n.(nEnv(MC) Interaction(G).(n=Begin()C =End()))


Behaviour models

Scenario diagramDescribes a typical situation in the operation of a system from an agent’s view. used in behaviour diagrams

behaviour diagramdefine behaviour rules of an agent


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)


Inter-Model ConsistencyBetween collaboration model and caste model

Constraint 4a) Every caste in a collaboration model CD must be a caste in the caste model C. Formally,

DCD.nNode(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,MBCM.(MB < MAR Aggr(C).(R(B,A))


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.

BBM.nNode(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.

BBM.aAgents(B).nNode(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.


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.

aVisibleActions(C).(rRules(BC) (MComponents(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.

ScScenarios(BC).GRef(Sc).GCollaborators(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. ScScenarios(B).GRef(Sc).(GEnv(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).

(aVisibleActions(C)).


Summary

Horizontal Consistency

Vertical Consistency

Local Global

Intra-model

Intra- diagram

1a, 1b, 1c, 1d, 1e, 2a, 2b, 3a, 3b, 3c

- -

Inter-diagram

2c, 2d, 2e, 2f, 2g, 2h, 2i, 3d

2j, 2k -

Inter-model 4f, 4g, 4h, 4i 4e 4a, 4b, 4c, 4d


Consistency check tools in CAMLE

Well-formedness conditions are checked during model construction in the process of interactive diagram editingOther consistency constraints are checked by a set of tools; each for one specific constraintConsistency checking tools are called in the following order to reduce the complexity of error handling:

Intra-model intra-diagram consistency checkersIntra-model inter-diagram consistency checkersInter-model local consistency checkersInter-model global consistency checkers


Architecture of CAMLE Environment

Diagram Editor

Partial Diagram Genera

tor

Well-formedness

Checker

Users’ Requirements

Graphic Models

Graphic User Interface

Model Manager

Formal Specifications

Specification Generator

Consistency Checker Control

ler

Collaboration Model CheckerCaste/

Collaboration Checker

Behaviour/Collaboration

Checker

Caste/Behaviour Che

cker

Behaviour Model Chec

ker

General/ Specific

CheckerCross level

Checker

Check Result


Case studiesUnited 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


Observations on case studiesIn 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


Conclusion Roles of consistency constraints in MDSD

Quality assurance in modelling processConsistency constraints can be defined to effectively improve the quality of models and the productivity in model constructionConsistency 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 workStatistical analysis of the effectiveness of consistency constraintsFurther development of CAMLE environment


References1. Shan, L. & Zhu, H. CAMLE: A Caste-Centric Agent Modelling

Language and Environment. Proc. of SELMAS at ICSE’04, Edinburgh, Scotland (UK), May 2004.

2. Zhu, H. SLABS: A Formal Specification Language for Agent-Based Systems, Journal of Software Engineering and Knowledge Engineering 11(5), 529-558, 2001.

3. 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, 83-90. 2001.

4. Nentwich, C., Emmerich, W., & Finkelstein, A. Flexible Consistency Check. ACM Transactions on Software Engineering and Methodology 12 (1), 28-63, 2003.

5. 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.

consistency check in modelling multi-agent systems

Documents

idea of consistency

systemensuring consistency

model consistency problem

software documentation

different views

set of consistent constraints

systems properties

type errorsdevice