1. Using UML for Modeling Complex Real Time System Architectures
Bran Selic
VP Advanced Technology
ObjecTime Limited

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
OMT
(Rumbaugh)
UML
1.4
Mar. 1999
UML
0.9
1996
Booch
UML
1.1
Nov. 1997
OOSE
(Jacobson)
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-Model–Example
GeneralizeableElement
isRoot:Boolean
isLeaf:Boolean
isAbstract:Boolean
(Meta)class
Generalization association
Feature
visibility:{public, protected, private} *
Classifier
Compostion association
Class
isActive:Boolean
not self.isAbstract implies self.allOperations->forAll(op | self.allMethods->exists(m | m.specification includes (op)))
OCL constraint

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

7. General Real-Time Systems
A system that maintains a continuous timely interaction with its environment
environment
Real-Time System
(state)
inputs
outputs
outputs = f (inputs, state)

8. 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

9. 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

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

11. Real-Time Software Architectures
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

12. Architectures and Evolution
Two functionally equivalent initial architectures: A C B A C B X A C B
Mediator X
Mediator

13. Real-Time Architectural Specifications
Example telecom system architecture
TerminalA
TerminalB
Channel1
Channel2
Structure
Application Layer
Services Layer
Behavior

14. Architectural Component Design
Library
System1
Channel1
Terminal
TerminalA
TerminalB
Channel2
Channel
System2
Terminal Tester
TerminalA
Terminal Tester

15. Refining Architectures (Reuse)
TerminalA
TerminalB
Channel1
TerminalA
TerminalB
Channel1
Channel2

16. 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

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

18. Business Modeling Library Real-Time Modeling Library (UML-RT)
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”
Business Modeling Library
Real-Time Modeling Library (UML-RT)
...
UML Modeling Concepts

19. UML Extensibility Mechanisms
Stereotypes, constraints, tagged values
Constraint (OCL)
Class
isActive:Boolean
not self.isAbstract implies self.allOperations->forAll(op | self.allMethods->exists(m | m.specification includes (op)))
stereotype
Capsule
<“ports” >
required tag

20. 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 (>100) of large-scale industrial projects
Tool support available (ObjecTime Limited and Rational Software)

21. 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

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

23. Capsules: Architectural Objects
Active objects
Encapsulation
shell
Ports

24. Capsules: Behavior
Optional hierarchical state machine (signal handler with run-to-completion semantics)
transitionS1toS2: {int x;
x = 0;
p2.send(s1); p3.send(s2); … }; S1 S2 S3 S1 S2

25. Capsules: UML Modeling
Stereotype of Class concept («capsule») with specialized (executable) semantics
Class diagram representation:
«capsule» CapsuleClassX
#counter : int #x : char
+portB : ProtocolA::master
#portC : ProtocolB
ports

26. Protocols: Contractual Behavior Patterns
Interaction contracts between capsules
e.g., operator-assisted call
Caller
Operator
Callee
time
call
ack
number
call
ack
transfer
talk

27. OperatorAssisted Call
Protocol Specifications
A special form of collaboration
OperatorAssisted Call
Alice
Bob
caller
callee
initial
connected
connecting
protocol state machine
operator
caller
operator
callee
significant sequences
Dexter
Charlie

28. Protocol Roles Specifies one party in a protocol OperatorRole
caller
operator
callee
significant sequences
signal
source
call
caller
number
ack
callee
Incoming signals
OperatorRole
signal
target
call
callee
transfer
caller
ack
Outgoing signals
initial
connected
connecting
role state machine

29. Extended OperatorRole
Protocol Refinement
Using inheritance
signal
source
call
caller
number
ack
callee
Incoming signals
signal
source
call
caller
number
ack
callee
Incoming signals
target
transfer
Outgoing signals
OperatorRole
reply
caller
signal
target
call
callee
transfer
caller
ack
Outgoing signals
Extended OperatorRole
query
caller

30. Protocols: UML Modeling
Collaboration stereotype: «protocol»
Classifier Role stereotype: «protocolRole» 1
«protocolRole» caller
«protocol» OperatorAssisted Call
ack
transfer
incoming 1 1
call
number
talk
outgoing
«protocolRole» operator
«protocolRole» callee

31. Ports: Boundary Objects
Fully isolate a capsule’s implementation from its environment (in both directions)
Environment
Capsule S1 S2
Created and destroyed along with their capsule

32. «capsule» CapsuleClassX
Ports and Protocols
Each port realizes a single protocol role (type)
Multiple ports with same type possible
«capsule» CapsuleClassX
+portA : ProtocolA::master
#portB : ProtocolB
+portC : ProtocolB~
ports

33. Ports: Collaboration Diagram Notation
«capsule» anX:CapsuleClassX
portA : ProtocolA::master
«port» portA:ProtocolA::master 1
portC : ProtocolB~
Shorthand notation for capsule instances
iconified form

34. «capsule» receiver : Fax
Combining Capsules
Using connectors
«capsule» sender : Fax
remote : FaxProt
«capsule» receiver : Fax
remote : FaxProt
Connector
Connectors model communication channels
Each connector supports a single protocol
Static typing rules apply (compatible protocols)
Modeled as association classes in UML

35. «capsule» receiver:Fax
Composition: Structural Patterns as (Reusable) Dynamic Components
Relay port
sendCtrl : Control
receiveCtrl : Control
«capsule» sender:Fax
remote:FaxProt
c : Control
«capsule» receiver:Fax
Remote:FaxProt
c : Control
FaxCall
The composite is also a first-class object!

36. 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

37. «capsule» receiver:Fax
End Ports: Where Structure and Behavior Meet
Ports directly connected to the state machine
Implementation End Port
Public End Port
c : SystemControl
«capsule» sender:Fax
c : Control
«capsule» receiver:Fax
initial
connected
connecting
capsule state machine
senderCtrl : Control~
receiveCtrl : Control~

38. Decomposition: Class Diagram View
Alternative representation
More abstract
«capsule» Fax 1
sender
«capsule» FaxCall 1
receiver

39. 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

41. Summary (2) Only four UML stereotypes are sufficient
(include formally defined constraints that ensure consistency/executability)
Stereotype
UML Metaclass
«protocol»
Collaboration
«protocolRole»
ClassifierRole
«port»
Class
«capsule»
Class
supplemented by an optional custom notation

42. Bibliography
Real-time architectural modeling whitepaper by B. Selic and J. Rumbaugh:
OMG’s UML 1.1 standard
ROOM
B. Selic, G. Gullekson, and P. Ward, “Real-Time Object-Oriented Modeling”,
John Wiley & Sons, NY, 1994.