Interoperability, Automation, Built-in Evolution: the DEVS Framework for Coping with Emerging

Complexity

Bernard P. Zeigler Arizona Center for Integrative Modeling and Simulation

University of Arizona, Tucsonand

RTSync Corporation

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IT Systems Developmental Complexity?

• IT Systems Developmental Complexity = degrees of developmental freedom

× interdependence of design decisions

× special requirements of environments

• IT Complexity explosion – is driven by faster, cheaper computers, networking, web middleware, …, – Emergence: each stage enables the next stage with accelerating options for

further growth– Wherever choices in platform, language,…, line of code, are possible, different

developers will make different choices– Underlying structure/behavior dependencies force local decisions to have

global impact breaking neat design patterns– Environments impose a plethora of special situations and an exponentially

growing number of parameter combinations.2

• Consequences of complexity explosion:– Proliferation of incompatible variations on same themes– Ubiquitous heterogeneity– Vertical integration - “Stove piping”

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Response: Model-Driven Development Methodology • is increasingly being adopted for software-intensive system development• In this context, model is an abstract representation of software code, that

– is technology independent– can survive technology changes– can be implemented in multiple code instantiations– enables reuse and automation

UML (Unified Modeling Language)

• Is the most widely used framework to support model driven development

• Promoted by Object Management Group as a standard within its Model Driven Architecture (MDA)

• Supported by increasingly powerful commercial tools• Enhanced by SysML supporting requirements front end• Incorporated in architectural frameworks: DoDAF,

MoDAF, …

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Issues In Developmental Complexity of IT Systems

• Often development does not start from scratch• Conditioned by idiosyncratic requirements • Powered, but unconstrained, by applicable standards• Requires legacy subsystem integration• Rigorous testing is needed to cope with complexity• Methodology must scale with growth and evolution of

system• UML/MDA offers only limited support to address these

concerns

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Formulate the Issues within a Formal System of System Models (SoSM) Concept

• SoSM = collection of disparate system models to be federated to satisfy new simulation requirements

• Each participating system model may itself be large and complex

• Participant models usually have become efficient at achieving their own specialized requirements

• Participant models often adhere to idiosyncratic formalisms and development approaches

• Distinguish between interoperation and integration to set appropriate objectives

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Interoperation vs Integration*

Interoperation of system components

• participants remain autonomous and independent

• loosely coupled• interaction rules are soft coded• local data vocabularies persist• share information via mediation

Integration of system components• participants are assimilated into whole,

losing autonomy and independence• tightly coupled• interaction rules are hard coded• global data vocabulary adopted• share information conforming to strict

standards

* adapted from: J.T. Pollock, R. Hodgson, “Adaptive Information”, Wiley-Interscience, 2004

NOT Polar Opposites!

reusabilitycomposability

efficiency

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DEVS Framework• Discrete Event Systems Specification (DEVS) is the basis for a formal framework

for modeling and simulation • DEVS contributes to scalability by:

– Offering a standard for distributed simulation to support interoperability, composability, and reuse

– Exploiting the separation between model, experimental frame and simulator– Fostering model continuity and progressive development– Automating and integrating complex systems implementation and testing– Emulating the biological brain for its "built-in" correlation of activity and

behavior to drive efficient evolution via component re-us

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DEVS is not a technique, method or technology… But it can leverage technology to add implement its

contributions … in particular Web Service Technology

Web Service Oriented Architecture Basis for M&S

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Language and platform independent =>separation of specification and implementation

Loosely coupled => message based, synchronous and asynchronous

interactions.Net-Centric =>

No centralized control, use of established protocols, security considerations.

Inter-operable =>Standards based

Observable => agents can inspect service requests/responses

Transport protocol HTTP/HTTPS request/response

Data Encoding SOAP (Simple Object Access Protocol), XML Schema

Interface Description WSDL (Web Services Description Language)

Service Description and Discovery UDDI (Universal Description, Discovery and Integration)

Security WS-Security, XML-Signature, XML-Encryption, ...

Emerging infrastructure =>Net-Centric Enterprise Services on the Global

Information GridBasis for Model Registration and Discovery =>

Meta-Data RegistryBasis for Simulation => Web server and service development frameworks

( .Net, AXIS)Emerging advances => Mediation services, Semantic Web

Data Type Schema and InstancesData Type Schema and Instances

SOAPSOAP

XMLXML

Network Layers

ServicesServices RegistriesRegistries DataData

Approach to Current Issues in SoSM

• Adopt Web-enabled M&S Concepts for composing SoSM

• Exploit SOA infrastructure for Model Repository and Component Reuse

• Develop Formal Dynamic SoSM Distributed Simulation Standard

• Build on this foundation to support Higher Levels of Interoperability

• Develop automated and integrated development and testing methodology

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SOA-enabled Model Repository Composability and Reuse *

* adapted from: ZEIGLER, B. P. 1997. A framework for modeling & simulation. Applied Modeling & Simulation:An Integrated Approach to Development & Operation, McGraw-Hill, New York.

Requirement In relation to Supports

Components and Coupling

Creating new compositions composabilityreusability

building block components for application areas

defining a small number of “primitives” for synthesizing a wide variety of models for specific domain

expressabilityreusability

hierarchical modular model construction

input/output ports for both building block components and coupled models

composabilitycomplexity management

experimental frame base indexing

supports discovery of frames instantiated in the model base that are related to a desired frame for given objectives

meta data characterizationdiscovery

accommodate multiple formalisms

enable using different types of models with specific semantics, advantages, and limitations

expressabiltyinteroperability

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Success Story: DEVS-based Joint MEASURE – Model Repository Reuse*

Note presence of discrete and continuous dynamic model typesNote presence of discrete and continuous dynamic model types

“… the Lockheed-Martin activities may well represent the state of the art in complex model composability …”,

Improving the Composability of Department of Defense Models and Simulations, P.Davis and R.Anderson RAND, 2004

GPS III

*Advanced Simulation Center, Lockheed Martin Corp., Sunnyvale, CA

Use of infrared model in JCTS

project

Use of infrared model in JCTS

project

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Linguistic Levels of Information Exchange and Interoperability

syntactic

semantic

pragmatic

syntactic

semantic

pragmatic

LinguisticLevel

A System of Systems or services interoperates at this level if :

Pragmatic – how information in messages is used

The receiver re-acts to the message in a manner that the sender intends (assuming non-hostility in the collaboration).

Semantic – shared understanding of meaning of messages

The receiver assigns the same meaning as the sender did to the message.

Syntactic –common rules governing composition and transmitting of messages

The consumer is able to receive and parse the sender’s message

System Participant System Participant13

DEVS Model SpecificationDEVS Model Specification

SOAPSOAP

XMLXML

DEVS Simulation ProtocolDEVS Simulation Protocol

Network Layers

ServicesServices

DEVS Standardization Supports Higher Level Web-Centric Interoperability

DEVS Protocol specifies the abstract simulation engine that correctly simulates DEVS atomic and coupled models

•Gives rise to a general protocol that has specific mechanisms for:•declaring who takes part in the simulation•declaring how federates exchange information•executing an iterative cycle that

controls how time advancesdetermines when federates exchange messagesdetermines when federates do internal state updating

DEVS Simulation Concept

DEVS Protocol

DEVSSimulator

DEVSModel

Note: If the federates are DEVS compliant then the simulation is provably correct in the sense that the DEVS closure under coupling theorem guarantees a well-defined resulting structure and behavior.

Note: If the federates are DEVS compliant then the simulation is provably correct in the sense that the DEVS closure under coupling theorem guarantees a well-defined resulting structure and behavior.

syntacticsemantic

pragmatic

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SchemataSchemata RegistryRegistry

Web-enabled interoperability of DEVS components

IP NetworkIP Network

DEVScoordinator

DEVScoordinator

DEVS coupledModel

DEVS coupledModel

DEVSJAVA client

JRE

DEVS Simulator ServicesIn C++

DEVS Simulator ServicesIn C++

DEVSModelDEVS

Model

aDEVS FederateaDEVS Federate

Microsoft web serverMicrosoft web server

.Net .Net

DEVS Simulator ServicesIn JAVA

DEVS Simulator ServicesIn JAVA

DEVSModelDEVS

Model

DEVSJAVA FederateDEVSJAVA Federate

Apache tomcat serverApache tomcat server

AXIS2

ProxiesProxies

DEVSMessages

DEVSNamespace

DEVSNamespace

SOAPmessages

• DEVS Message Class is defined in the formalism• Schemata for entity classes in Message are stored in namespace• DEVS Federates can register and discover schemata for information exchange

• DEVS Message Class is defined in the formalism• Schemata for entity classes in Message are stored in namespace• DEVS Federates can register and discover schemata for information exchange

Supports re-use, composability, andinteroperability

Supports re-use, composability, andinteroperability

Can be automated for JAVA using Dynamic Invocation

Can be automated for JAVA using Dynamic Invocation

Simulator Services

Simulator Services

Non-DEVS Federate Non-DEVS Federate

web serverweb server

Biologically Inspired Assessment for Component Re-use

DEVS Simulator Services

DEVS Simulator Services

DEVSModelDEVS

Model

DEVS FederateDEVS Federate

Web serverWeb server

DEVScoordinator

DEVScoordinator

DEVS coupledModel

DEVS coupledModel

DEVS Coordinator

JRE

IP NetworkIP Network

DEV

SAg

ent

DEV

SAg

ent

Mission ThreadEvaluation

Mission ThreadEvaluation

ActivityTracking

ComponentCredit

Assignment

ComponentCredit

Assignment

Information for Future Component Re-use

HttpRequests/responses

Correlations of activity with Mission Thread Success

Correlations of activity with Mission Thread Success

Component benefit and resource cost in context

Component benefit and resource cost in context

collector

collector

DEVS-Based Net-Centric Systems Test Agent Capability

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Mission Thread

Information Exchange

Network Monitoring

Middleware

Mission Effectiveness

System Performance

PragmaticAgents

SemanticAgents

SyntacticAgents

T&E Instrumentationsites

servers

usersclients

networks

workstations

Summary • Model-driven methodology employs technology-independent software

abstractions, e.g., in UML, to support diverse implementation platforms and enable reuse and automation

• Existing interoperability standards do not provide needed separation between models and simulations and do not effectively constrain object models

• System of System Modeling (SoSM) concepts go beyond UML/MDA to address issues in interoperability, composability, and reuse

• DEVS system theory –based framework operationalizes SoSM concepts and supports automated, rigorous testing in realistic GIG/SOA environments

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devsworld.org www.acims.arizona.edu Rtsync.com

Books and Web Links

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More Demos and Links http://www.acims.arizona.edu/demos/demos.shtml

• Integrated Development and Testing Methodology: • AutoDEVS (ppt) & DEMO

– Natural language-based Automated DEVS model generation – BPMN/BPEL-based Automated DEVS model generation

– Net-centric SOA Execution of DEVS models

– DEVS Unified Process for Integrated Development and Testing of SOA

• Intrusion Detection System on DEVS/SOA

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DEVS/SOA Infrastructure: Supports Deployment and Execution of DEVS Models on the Web

WEBSERVICECLIENT

Middleware (SOAP, RMI etc)Net-centric infrastructure

DEVS Simulator Services

DEVS Modeling Language (DEVML)

DEVSJAVA

DEVSAgent

( Virtual User)

DEVSAgent

(Observer)

WEBSERVICECLIENT

Run Example

• Service Oriented Architecture (SOA) consists of various W3C standards

• Machine-to-machine interoperable interaction over the network based on WSDL interface descriptions

• Client server framework

• Message encapsulated in SOAP wrapper which is in XML

1. MAJ Smith tasks Intel to reconnoiter objective area and provide threat estimate

2. Posts taskings using Discovery and Storage

5. Intel Cell issues alert via messaging 6. MAJ Smith pulls estimate from Storage

3. Intel Cell initiates high priority collection against objective, and collectors post raw output

4. Intel posts products via Discovery and Storage

Observing Agent for Major Smith

Observing Agent for Intel Cell

NCES GIG/SOA

• Test agents are DEVS models and Experimental Frames

• They are deployed to observe selected participant via their service invocations

notes time of posting

Observing Agent alerts other Agent

Computes Time for Task,Measure Performance

sends time to other Agent

Example of GIG/SOA Example of GIG/SOA Mission Thread TestingMission Thread Testing

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