Service Behavior Consistency in the OSGi Platform

IntelligentIntelligent SSpacepace國立台灣大學資訊工程研究所智慧型空間實驗室國立台灣大學資訊工程研究所智慧型空間實驗室

Service Behavior Consistency Service Behavior Consistency in the OSGi Platformin the OSGi Platform

AuthorsAuthors

Y.Qin, H.Hao,L.Jun , G.Jidong and L.JianY.Qin, H.Hao,L.Jun , G.Jidong and L.Jian

Proceedings of 12th Asia-Pacific Software Engineering Conference (APSEC’05)

(acceptance rate ~= 29%)

ReporterReporter

C.F.Liao (C.F.Liao ( 廖峻鋒廖峻鋒 ))

Feb 15,2007Feb 15,2007


2/30

OutlineOutline

PreliminariesPreliminaries Behavior Inconsistency Behavior Inconsistency ProblemProblem The Proposed The Proposed SolutionsSolutions

Service Behavior Modeling Verification of Service Behavior Consistency

Implementation Implementation skippedskipped ConclusionConclusion


3/30

220 V

110V

Reusable Component

Structural Consistent

Structural Consistent but Behavioral Inconsistent!

What this Paper is Talking About?What this Paper is Talking About?


4/30

Making Software ReusableMaking Software Reusable

openTV(), X.10

Invoker

openTV(),UPnP

Invoker

When you modify service X,You have to rewrite all of it’s invokers!


5/30

Interface As Service SpecificationInterface As Service Specification

Spec of openTV()(Interface)

Invoker

X.10 Implementation of openTV()

UPnP Implementation of openTV()

The developers can substitute the service implementations without affecting the invoker.


6/30

Substitutable ComponentsSubstitutable Components

We can substitute Service A with Service B without affect overall system behavior iff

Service A is Structural Consistent with Service B w.r.t. a common interface I


7/30

Term DefinitionsTerm Definitions

Service Client / Service Invoker

Service Specification / Interface

Service Implementation / Component / Service


8/30

Formal Definitions of Interfaces and Formal Definitions of Interfaces and ServicesServices

Service Specification (interface)Service Specification (interface)

Service ImplementationService Implementation

),( IFIF MIIF

A set of exported methods of IFUnique id of IF

),( SS MIS

Unique id of S A set of exported methods of S


9/30

Structural ConsistencyStructural Consistency

SASA is is

Structural ConsistentStructural Consistent with with

SB SB

w.r.t w.r.t An InterfaceAn Interface IFIF

if and only ifif and only if

SAIF MM SBIF MM and

LogService

LogService

SA

SB

log

log


10/30

Structural Consistency – An ExampleStructural Consistency – An Example

},,,{

},,{

},,{

finalizelogDBloginitM

finalizeloginitM

finalizeloginitM

ceDBLogServi

ServiceConsoleLog

LogService

ceDBLogServiLogService MM ServiceConsoleLogLogService MM

log finalizeinit

LogService

log finalizeinit

logfinalizeinit logDB

Given

We can obtain that

So ConsoleLogService is Structural Consistence with DBLogService w.r.t.LogService

ConsoleLogService

DBLogService


11/30

Enhanced Structural Consistency in OSGiEnhanced Structural Consistency in OSGi

OSGi enhances structural consistency by specifOSGi enhances structural consistency by specifying “Properties” of components.ying “Properties” of components.

Format:Format: RFC 1960: ”A String Representation of LDAP search f

ilters”

Example:Example:

&(DeviceName=TV2) (Size=21)&(DeviceName=TV2) (Size=21)

|(vendor~=HP)(!(dpi<=300))(type=printer)|(vendor~=HP)(!(dpi<=300))(type=printer)


12/30

OSGi ServicesOSGi Services

),,( SSS MPIS

Unique id of S A set of exported methods of S

A set of properties of S

We can revise the previous definition of a Serviceto the following form:


13/30

Behavioral ConsistencyBehavioral Consistency

Proposed by Proposed by B.Liskov and N.Belkhatir at 1994 in the ACM Trans on PLS. The interface mechanism in traditional OOP only guar

antees Structural Consistency The implementations may have unexpected behavio

r even if they are Structural Consistent.

Behavior A matter of call sequences from the Service Client!


14/30

220 V

The Problem of Structural ConsistencyThe Problem of Structural Consistency

Structural Consistency only guarantees the Structural Consistency only guarantees the service implementations are service implementations are structurally structurally compatiblecompatible with each other. with each other.

The The underlying behaviorunderlying behavior of methods may of methods may different.different.

What if the 110V and 220V have the same socket shape?What if the 110V and 220V have the same socket shape?

110V


15/30

Behavior Consistency – An Example(1)Behavior Consistency – An Example(1)

log finalizeinit

LogService

init

log

finalize

ConsoleLogService

log finalizeinit


16/30

Behavior Consistency – An Example(2)Behavior Consistency – An Example(2)

log finalizeinit

LogService

init

log

finalize

logDB

logfinalizeinit logDB

DBLogService

The expected call sequences of LogService is different from that of DBLogService !


17/30

Ensuring the Behavior ConsistencyEnsuring the Behavior Consistency

Behavior ModelingBehavior Modeling Workflow Net an extension of Petri Net to model th

e workflow management systems. Proposed by W.M.P. van der Aalst in ATPN 1997.

Consistency ValidationConsistency Validation Observation / Invocation Behavior Consistency Theor

y Proposed by J.Ebert and G. Engels in 1994.


18/30

Behavior Model (BM)Behavior Model (BM)

),,,,,( TMoiFTPBM

)()( PTTPF

BM is essentially a Workflow Net except TM is redefined.BM is essentially a Workflow Net except TM is redefined.

Places

Transitions

Directed Arcs

Input place / output place

A function that assigns each transition to a method

}){(: SMTTM


19/30

Summary: Revised Definition of ServiceSummary: Revised Definition of Service

),,,( SSSS BMMPIS

),,,,,( SSSSSSS TMoiFTPBM

}){(: SSS MTTM


20/30

Invocation ConsistencyInvocation Consistency

Service S1’s Behavior ModelService S1’s Behavior Model

is is invocation consistentinvocation consistent with S2’s Behavior Model with S2’s Behavior Model

ifif

S1BM

S2BM

12 SS BMBM LMSLMS

What is LMS ?


21/30

Legal Method Sequence (LMS)Legal Method Sequence (LMS)

Can be derived by depth-first traversal on a Can be derived by depth-first traversal on a Reachability GReachability Graphraph of a Petri Net. of a Petri Net.

Depth-First Traversal

}

{

finalize)logFile,logDB,(init,,

finalize)logDB,logFile,(init,

logFile),logDB,(init,logDB),logFile,(init,

logDB),(init,logFile),(init,init,LMS ceDBLogServi


22/30

Invocation Consistency - ExampleInvocation Consistency - Example

}{ finalize)log,(init,log),(init,init,LMSLogService

}

{

finalize)log,logDB,(init,,

finalize)logDB,log,(init,

log),logDB,(init,logDB),log,(init,

logDB),(init,log),(init,init,LMS ceDBLogServi init

log

finalize

LogService

init

log

finalize

logDB

DBLogService

ceDBLogServiLogService LMSLMS


23/30

init

logDB

finalize

LogService

Invocation Consistency isn’t Enough !Invocation Consistency isn’t Enough !

}

{

finalize)logDB,(init,

logDB),(init,init,LMSLogServiceBM

}

,

{

finalize)logDBEnc,(init,

finalize)logDB,(init,

logDBEnc)(init,logDB),(init,init,

LMSceDBLogServiBM

init

logDB

finalize

logDBEnc

DBLogService

ceDBLogServiLogService LMSLMS


24/30

Method ProjectionMethod Projection

}{ finalize)log,(init,log),(init,init,LMSLogServiceBM

}

{

finalize)log,logDB,(init,,

finalize)logDB,log,(init,

log),logDB,(init,logDB),log,(init,

logDB),(init,log),(init,init,LMSceDBLogServiBM

)}{)( finalizelog,(init,log),(init,init,LMSceDBLogServiLogService BMM


25/30

Observation ConsistencyObservation Consistency

Service S1’s Behavior ModelService S1’s Behavior Model

is is observation consistentobservation consistent with S2’s Behavior Model with S2’s Behavior Model

ifif

S1BM

S2BM

212)(

SSS BMBMM LMSLMS LogService

DBLogService

log

init

logDB

finalize


26/30

Observation Consistency - ExampleObservation Consistency - Example

init

log

finalize

LogService

init

log

finalize

logDB

DBLogService)},(

,

{

)(

finalizeinit

finalize)log,(init,

log),(init,init,

LMSceDBLogServiLogService BMM

LogServiceceDBLogServiLogService BMBMM LMSLMS )(

}

{

finalize)log,(init,

log),(init,init,LMSLogServiceBM


27/30

Verifying Behavioral ConsistencyVerifying Behavioral Consistency

The Service Implementation The Service Implementation SS is is Behavioral ConsistentBehavioral Consistent wit with Service Specification h Service Specification II iff : iff :

ISI BMBMM LMSLMS )(SI BMBM LMSLMS (S is (S is invocation consistentinvocation consistent with I) with I)

(S is (S is observation consistentobservation consistent with I) with I)

(The proof of this theory is in [J.Ebert and G. Engels 94])


28/30

Summary (1)Summary (1)

Structural Consistency(Traditional OOP Reuse)

Enhanced Structural Consistency(OSGi Service Reuse) Behavioral Consistency

[Liskov et al.94]

Modeling: UMLVerification: Language Mechanism

Modeling: UMLVerification: OSGi Platform

Modeling: Workflow NetVerification: IC / OC theorems

SAIF MM SBIF MM and

Key=value


29/30

Summary (2)Summary (2)

Behavioral Consistency[Liskov et al.94]

Modeling: Workflow NetVerification: IC / OC theorems

Behavioral Subtyping[Liskov et al.94]

MotivationProblem Modeling

Workflow Net[W.M.P. van der Aalst 97]

OSGi Component Model

Problem DomainReachability Graph/ LMS

Methodology Integration / Mapping

IC / OC Theorems[J.Ebert et al.94]

Solution Prototype

Multi-Service CoordinationBehavioral Consistency

Extension

SOBECA

Implementation


30/30

CommentsComments

This paper provides formal modeling methods of This paper provides formal modeling methods of reusable components.reusable components. However, many errors in this paper.

Petri Net modeling will be more valuable if used Petri Net modeling will be more valuable if used to model distributed / concurrent components.to model distributed / concurrent components.

Stateful is considered harmful in service design, Stateful is considered harmful in service design, does the behavior consistency really matter?does the behavior consistency really matter?

Documents

Service Behavior Consistency in the OSGi Platform