technische universiteit eindhoven 25 september 2002btheelen1 using the she method for uml-based...

25 September 2002 www.ics.ele.tue.nl/~btheelen 1

technische universiteit eindhoven

Using the SHE Method forUML-based Performance Modelling

B.D. Theelen



Contents• Introduction• Software/Hardware Engineering (SHE)• UML Profile for SHE

– Parallel Object-Oriented Specification Language (POOSL)

• Performance Evaluation• Tool Support• Conclusions



Introduction• Designing complex hardware/software systems entails evaluating

the performance of several design alternatives• System-level design methods

– Present frameworks for developing executable modelsexecutable models, which• Describe a system in the early phases of the design process• Abstract from many implementation details (which are not all known yet)• Allow analysing performance properties before actually realizing the system in

hardware and software• Enable to take well-founded design decisions based on analysis results

– Provide heuristicsheuristics for applying certain modelling languagesmodelling languages and performance analysis techniquesanalysis techniques

– Are supplemented by toolstools that enable efficient application of analysis techniques by executing executing models according to semantics of modelling language

• UML is often used as modelling language



UML-based Performance Modelling• UML provides ample notation to specify a system, but

– InformalInformal dynamic semantics of UML diagrams complicates application of formalformal (mathematical) performance analysis techniques• Semantics of UML does not describe how to manage concurrency and time• UML models are in principle not executablenot executable

• A formal (mathematically defined) semantics would– Allow integral application of mathematical analysis techniques– Enable unambiguous executionunambiguous execution based on mathematical framework

• Software/Hardware Engineering (SHE)– System-level design method for complex real-time hardware/software

systems– Heuristics for developing UML models that can be transformed into formal formal

executable modelsexecutable models using the Parallel Object-Oriented Specification Language



SHE: three phasesConcepts & Requirements

ConceptModel

Questions

ExecutableModel

FormalProperties

ConceptsSatisfy Requirements

Formulation

Evaluation

FomalisationValidation Fomalisation

Component-Level Design

Milestone A

Milestone C

Milestone B

Sys

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vel

Des

ign

Fo

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lati

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Fo

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Yes

No

• Formulation– UML profile for SHEUML profile for SHE– Commercial tool

• Formalisation– Modelling language POOSL

• Small set of expressive primitives• Formal semantics defines how to

handle concurrencyconcurrency, timetime and stochasticitystochasticity in POOSL model

– SHESimSHESim tool• Performance evaluation

– Based on Markov chain analysis• Analytic computationcomputation or

estimation by simulationsimulation– RotalumisRotalumis tool



UML Profile for SHE: Data Objects

• Model passive resources (information)• Organised in data classesdata classes• Attributes are instance variablesinstance variables• Procedural behaviour specified with methodsmethods• Receiving messages results in atomic atomic

executionexecution of equally named method• Similar to objects in traditional OO languages

Na

me

Att

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Me

tho

ds

Me

ssa

ges

<<data>>Packet

<<instance variable>>Length: IntegerDestination: Integer

<<method>>setLength(L: Integer): PacketgetDestination(): Integer

• Instances of data class RandomGeneratorRandomGenerator introduce stochasticity– Examples: state transition probabilities in state charts, probabilistic delays, …

• Library classes for random variables of various distributions



UML Profile for SHE: Processes

Na

me

Att

ribu

tes

Me

tho

ds

Me

ssa

ges

<<process>>Switch_Core

<<instance parameter>>SwitchDelay: Real

<<instance variable>>P: Packet

<<method>>TransferPacket(ID: Integer)()

<<initial method>>Init()()

<<message>>In?PacketOut!Packet

• Model real-time behaviour of non-composite active resources (components)

• Organised in process classesprocess classes• Attributes

– instance variablesinstance variables– instance parametersinstance parameters

• Perform behaviour asynchronously concurrent• Behaviour specified with sequentially or

concurrently executed methodsmethods• Initial methodInitial method defines start behaviour• Synchronously pass messages (and data) over

static channelsstatic channels through ports



• Behaviour specified in state charts, activity diagrams, collaboration diagrams and message sequence charts

• Orthogonal POOSL statements– Method abstraction m(E1…Ei)(p1…pj)– Parallel and sequential composition par S1 and S2 and … rap S1; … ; Sn

– Synchronous message passing c!m(E1…Ei){Eat} c?m(p1…pi|Erc){Eat}– Non-deterministic selection sel S1 or S2 or … les– Guarded and atomic execution [E]S {E1; E2; … Ei}– Interrupt and abort interrupt S1 with S2 abort S1 with S2

– Loops and choice while E do S od if E then S1 else S2 fi– Data Expression E– Empty behaviour skip– Time synchronisation delay E

• Full support for modelling behavioural hierarchybehavioural hierarchy• Limited number of heuristics for deriving POOSL code provided

Behaviour of Processes



UML Profile for SHE: Clusters

Na

me

Att

ribu

tes

<<cluster>>Internet_Router

<<instance parameter>>SwitchDelay: Real

• Model composite active resources (components)• Organised in cluster classescluster classes• Attributes are instance parametersinstance parameters• Do notnot define additional behaviour• Express structural hierarchystructural hierarchy originating from

aggregation relations between components

Internet_Router

Inputs ToSwitch

A B

FromSwitch Outputs

Output_Buffers

FlowControl

OutIn

Sinks

In

Switch_Core

OutIn

A B

Input_Buffers

In

FlowControl

Out

Sources

Out

Instance Instance Structure Structure DiagramDiagram



Framework for Performance Evaluation• Mathematical framework based on formal semantics of POOSLMathematical framework based on formal semantics of POOSL• Formal semantics combines aspects of traditional OO languages

with probabilistic timed version of process algebra CCS• POOSL model defines a unique Markov decision process

Formal SemanticsFormal Semantics

Understandable POOSL Model

Markov Decision Process

• Formalisation of performance related aspects in UML diagrams involves extendingextending a POOSL model to define a reward structure– Example: variable to denote current occupancy of a buffer

+ Extensions for Performance Evaluation

+ Reward Structure

External SchedulerExternal Scheduler

• External scheduler (simulator) resolves non-determinismnon-determinism

Discrete-Time Markov Chain + Reward Structure

• Mathematically analysable discrete-time Markov chaindiscrete-time Markov chain



• Analytical computationcomputation: ergodic theorem for Markov chains– Example: time-average buffer occupation

Occupation Average )(

)()(

)(

)()(a.s.

1

1

SS

SS

n

ii

n

iii

Stπ

StSOccupationπ

Xt

XtXOccupation

N(0,1) σ

μ)(1

μ then )(1

if d.1a.s.

1

n

iin

ii

XPacketLostn

nXPacketLostn

Performance Evaluation

• Estimation by simulationsimulation: central limit theorem for Markov chains– Example: packet-loss probability

– Enables accuracy analysis with confidence intervalsconfidence intervals– Enables automatic terminationautomatic termination of simulation when results are accurate– Library classes for analysing accuracy of different average and variance types



Tool Support• SHESim

– Incremental formalisationformalisation of UML models into POOSL model– Defining cluster classes based on drawing instance structure diagrams– Specifying process classes– Defining data classes



Tool Support• SHESim

– Interactive validationvalidation by inspectionof objects during simulation

– Validation against• Collaboration diagrams• Message sequence charts• State charts and activity diagrams• Use case diagrams / scenarios



Tool Support• Rotalumis

– High-speed execution of large POOSL models for performance evaluationevaluation– Translates POOSL model into byte code that is executed on virtual machine

implemented in C++– Displays limited information about progress of simulation– Performance results are logged to files (based on the library classes)



Conclusions• Performance modelling requires language with formal semantics

– Unambiguous execution based on mathematical framework– Integral application of mathematical analysis techniques

• System-level design method SHE distinguishes three phases– Formulation based on informal UML diagrams (UML profile for SHE)– Formalisation with formal modelling language POOSL

• POOSL model implicitly defines Markov chain– Evaluation based on Markov chain analysis

• Analytical computation or estimation by simulation• Library classes for accuracy analysis

• SHE offers tools for formalisation and evaluation phases– SHESim for creation and validation of POOSL models– Rotalumis for fast evaluation large POOSL models

• Future research on tool integrating computer support for all phases

technische universiteit eindhoven 25 september 2002btheelen1 using the she method for uml-based...

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