Using UML for Modeling Complex Real Time System Architectures

1
Using UML for Modeling Complex Real Time System
Architectures

• Bran Selic
• VP Advanced Technology
• ObjecTime Limited
• bran_at_objectime.com

2
Overview

• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

3
The Unified Modeling Language

• A general purpose OO modeling language
• combines a number of proven methods

Catalysis
ROOM
etc.
4
What is (in) the UML Standard?

• Semi-formal semantic meta-model
• defines basic modeling concepts
• object, class, etc.
• includes well-formedness rules expressed as
  formal constraints in Object Constraint Language
  (OCL)
• Graphical notation for modeling concepts
• 8 different diagram types
• Two predefined domain extensions

5
The UML Meta-ModelExample
(Meta)class
Generalization association
Classifier
Compostion association
not self.isAbstract implies
self.allOperations-gtforAll(op
self.allMethods-gtexists(m
m.specification includes (op)))
OCL constraint
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• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

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General Real-Time Systems

• A system that maintains a continuous timely
  interaction with its environment

Real-TimeSystem (state)
outputs f (inputs, state)
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Complex Real-Time Systems

• Complex real-time systems characterized by
• extreme dependability (reliability, availability)
• diverse and feature-rich functionality
• continuous feature upgrades (evolutionary
  requirements)
• physical distribution
• Encountered mostly in telecommunications,
  defense, aerospace, and industrial control

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Modeling Requirements for Complex RT Systems

• This complexity requires focussed modeling
  support in at least the following areas
• Architectural modeling
• Timeliness and performance modeling
• Time-aware communication models
• Concurrency management
• Resource modeling
• Distributed system modeling
• Fault-tolerance techniques

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• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

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Real-Time Software Architectures

• Architecture
• The organization of significant software
  components interacting through interfaces, those
  components being composed of successively smaller
  components and interfaces
• It is the key to success in
• the initial construction of a system
• system evolution

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Architectures and Evolution

• Two functionally equivalent initial architectures

X
X
Mediator
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Real-Time Architectural Specifications

• Example telecom system architecture

Application Layer
Services Layer
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Architectural Component Design
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Refining Architectures (Reuse)
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Summary Requirements for Architectural Modeling

• The ability to model and enforce
• large-grain (architectural) components and their
  interfaces
• structural compositions of architectural
  components
• dynamic interaction patterns between
  architectural components
• refinement of architectures

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• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

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Approach and Method

• The necessary architectural modeling capabilities
  can be found in ROOM
• Express the architectural modeling concepts of
  ROOM using standard UML
• Domain-specific library of UML macros

Real-TimeModelingLibrary (UML-RT)
BusinessModelingLibrary
...
UML Modeling Concepts
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UML Extensibility Mechanisms

• Stereotypes, constraints, tagged values

Constraint (OCL)
not self.isAbstract implies
self.allOperations-gtforAll(op
self.allMethods-gtexists(m
m.specification includes (op)))
stereotype
required tag
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Real-Time Object-Oriented Modeling (ROOM)

• Domain-specific (real-time) concepts
• dynamic high-level structures
• reactive behavior (ROOMcharts)
• Executable (formal) models
• Full automatic code generation
• Field proven in a large number (gt100) of
  large-scale industrial projects
• Tool support available (ObjecTime Limited and
  Rational Software)

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Phasing

• Basic modeling capabilities (UML 1.1)
• structural pattern modeling (collaboration
  diagrams)
• state machine modeling
• Real-time specific constructs
• architectural modeling (March 98)
• other constructs (-June 99)
• collaboration ObjecTime Rational
• OMG standardization (1999/2000)
• RT analysis and design WG

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• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

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Capsules Architectural Objects

• Active objects

Encapsulation shell
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Capsules Behavior

• Optional hierarchical state machine (signal
  handler with run-to-completion semantics)

S1
S2
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Capsules UML Modeling

• Stereotype of Class concept (capsule) with
  specialized (executable) semantics
• Class diagram representation

capsuleCapsuleClassX
counter intx char
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Protocols Contractual Behavior Patterns

• Interaction contracts between capsules
• e.g., operator-assisted call

Caller
Operator
Callee
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Protocol Specifications

• A special form of collaboration

OperatorAssistedCall
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Protocol Roles

• Specifies one party in a protocol

OperatorRole
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Protocol Refinement

• Using inheritance

ExtendedOperatorRole
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Protocols UML Modeling

• Collaboration stereotype protocol
• Classifier Role stereotype protocolRole

protocolRolecaller
protocolOperatorAssistedCall
protocolRolecallee
protocolRoleoperator
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Ports Boundary Objects

• Fully isolate a capsules implementation from its
  environment (in both directions)

Created and destroyed along with their capsule
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Ports and Protocols

• Each port realizes a single protocol role (type)
• Multiple ports with same type possible

capsuleCapsuleClassX
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Ports Collaboration Diagram Notation
capsuleanXCapsuleClassX
portA ProtocolAmaster
portC ProtocolB

• Shorthand notation for capsule instances
• iconified form

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Combining Capsules

• Using connectors

Connector
Connectors model communication channels Each
connector supports a single protocol Static
typing rules apply (compatible protocols) Modeled
as association classes in UML
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Composition Structural Patterns as (Reusable)
Dynamic Components
Relayport
FaxCall

• The composite is also a first-class object!

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Composite Capsule Semantics

• Architectural assertion mechanism the static
  elements of the internal structure of a composite
  capsule are automatically created (and destroyed)
  along with the capsule
• applies recursively down to the innermost leaf
  capsule level
• only explicitly prescribed architectural
  structures can be instantiated
• This also significantly reduces the complexity of
  the model since all the code used to establish
  these structures is eliminated

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End Ports Where Structure and Behavior Meet

• Ports directly connected to the state machine

Public End Port
ImplementationEnd Port
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Decomposition Class Diagram View

• Alternative representation
• More abstract

capsuleFax
capsuleFaxCall
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• The Unified Modeling Language (UML)
• Complex real-time systems
• Requirements for modeling architectures of
  complex RT systems
• Approach and method
• Architectural modeling constructs
• Summary

40
Summary (1)

• Complex real-time systems phenomena require
  specialized modeling support
• The ROOM language has industry-proven support for
  modeling complex real-time architectures
• The benefits of both UML and ROOM are gained by
  expressing the ROOM constructs as UML stereotypes
• UML-RT a UML extension for the complex
  real-time domain

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Summary (2)

• Only four UML stereotypes are sufficient
• (include formally defined constraints that ensure
  consistency/executability)

• supplemented by an optional custom notation

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Bibliography

• Real-time architectural modeling whitepaper by B.
  Selic and J. Rumbaugh
• http//www.objectime.com
• OMGs UML 1.1 standard
• http//www.rational.com
• ROOM
• B. Selic, G. Gullekson, and P. Ward, Real-Time
  Object-Oriented Modeling,
• John Wiley Sons, NY, 1994.