ConnieApplying Aspec..

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Applying Aspect Oriented Modelling to Service Orchestration

Crest Centre, King’s College London

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Agenda

• Service Workflow – Orchestration

• Cross Cutting Concerns in Workflow

• Applying Aspect Oriented Modelling & Design

• Testing Service Orchestration

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Motivation of Research

• Business models shift from products to services

• Software as Services (SaaS) model of development - Components are not owned

• Service Oriented Architecture – Integrated modular architecture

• Mechanisms that allow well integrated services are difficult to provide – Service Workflows in WS- BPEL standard

• Cross-cutting concerns – Tangled workflow problem

• Aspect-Oriented Software Development (AOSD) offers means to disentangle cross-cutting concerns

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Service Workflows – BPEL

• Mechanisms that allow well integrated services are difficult to provide – Service Workflows in WS- BPEL standard

• Processes could only be decomposed according to the control flow

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Service Workflows – Tangled Cross Cutting Concern

Problem• Concerns that do not align with this decomposition become

scattered across the process description, making it difficult to manage

• Need a means to manage complexity

• To disentangle cross-cutting concerns

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Aspect Oriented Modelling & Design

• AOP emerged to complement O.O.Programming

• Models Cross cutting concerns – modularised concerns,

making development, maintenance and reuse easier.

• Enable non-invasive addition of concerns – support

software evolution

• Web service to meet post-deployment requirements

Update

aspect Update { pointcut change(): execution(void point.setX(int)) || execution(void point.setX(int)) || execution(void shape.moveBy(int,int))

after() returning: change() { Display.update(); } }

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Opportunities for AOSD in (SOA)

• Service Monitoring: detect conditions or

violation of properties at run-time.

– or a particular sequence of events has

occurred.

– Design by Contract

• Service Verification - testing

• Service Adaptation – e.g. QoS Requirements

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Current AOSD Approaches

• Domain Specific Aspect Language Extensions

– Doxpects, AO4BPEL

• Aspects Aware Execution Environment

– AO4BPEL, Small Talk Implementation

– WSFL implemented in JAsCO

• Limitations– Proprietary solution– Portability

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Problems Identified

• The Proprietary Technology Problem

– Standard Workflow Engines need to be modified

substantially

• In Aspect Deployment

– The Fragile PointCut Problem

– Joinpoint Detection Problem

• Modularisation Problem in Service

Middleware

– Address Infrastructural Concerns as AOP-WS-Middleware

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Proposed Solution• A framework of A.O. design that provides WS

composition support

• XQuery as the PointCut language

• Aspect Representation in XML

• Model Based Transformation for weaving & deployment

PointCut

JoinPoint

Advice

Aspect Schema .xsd

.wsdl Advice Logic

XSLT Rules .xsl Pointcuts &Joinpoints

Aspects Representation

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Aspect Weaving & Deployment

• Weaving – the process that coordinates aspects and non-aspects code

• Static Weaving

– Weaving Before Run-time

• Dynamic Weaving

– Allows for dynamically add, remove or refine aspects

– Difficulties are:

• Performance overhead

• Dedicated execution platform

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Static Weaving

New BPEL Process Description

Static Aspect Weaver

BPEL Process Aspect

Definition Aspect Deployment Description

Standard BPEL Execution EnvironmentStandard BPEL Execution Environment

1. Extract xsd from .bpel

2. <aspect>.xml & xsd

3. Transformation Rules

1. Locate pointcut

2. Joint point merge

4. Composing new .bpel

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Aspect Definition in XML1 <aspect name="Billing">2 <using>3 <namespace name="xmlns:bill" uri="my.billing.uri" />4 <partnerLink name="billing" partnerLinkType="bill:billingLT" />5 <variable name="billingMsg" type="bill:billingMsg" />6 </using>7 <pointcut name="CallStarts(Jp)"8 pointcut="invoking(Jp, ‘CallService’, ‘confCallPT’, ‘createConfCall’)" />9 <pointcut name="CallEnds(Jp)"10 pointcut="invoking(Jp, ‘CallService’, ‘confCallPT’, ‘closeConfCall’)" />11 <advice name="billService">12 <invoke partnerLink="billing" portType="bill:billingPT"13 operation="billService" inputVariable="billingMsg" />14 </advice>15 </aspect>

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Service Implemented Aspect

Definition of Service Implemented Aspects in WSDL:<complexType name="EPmessage">

<all> <elementname="opName" type="string"/> <element name="serviceType" type="string"/> <element name="serviceEndpoint“ type="EndpointReference"/> <element name="value" type="Serializable"/>

</all> </complexType><message name="MessageReceived">

<part name="MsgReceived“ type="tns:EPmessage"/> </message> <portType name="EndPointMonitorPT">

<operation name="SendRequest"> <input message="MessageSent"/>

</operation>

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Model Based Transformation

- Weaving and aspect deployment- Process of manipulating the meta data of the process schema

- MDA – model based transformation- General purpose languages – no overhead- Generic transformation tools: Graph transformation - Case tools: UML based - Dedicated Tools: QVT- Complexity- Kermeta & Eclipse EMF

Aspect Logic

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Case Studies

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Testing Service Workflows

• Service Orchestration - BPEL’s claim v.s. BPMN– Translation between the two processes

• Aspect-Oriented Testing Techniques

• Testing Woven Apects

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Evaluation Metrics

• AOSD Evaluation

– Multi-Dimensional Separation of Concerns

– Good Design vs. Good Coding

– Performance Bottleneck

– AOSD decomposition:

• Units of aspects

• Well-defined interfaces

• SOA Evaluation

– Comparable with component based software

– SOA is an example of Distributed Computing

• Decomposition of systems into functional or logical components with well-defined interfaces used for communication

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Aspect View – Customised view of the System

. . .

orchestration

choreography

Aspect Interface

Internal service/API

Presentation of Data

Transformation

Transformation

AOSD in WS Processes & Infrastructural Concerns

Data

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Future Directions• Dynamic AOP, uses wrapper technologies, offers a way of allowing

components to be individually customized and extended. – Dynamic aspect-oriented programming is relatively straightforward in a trusted

environment, where (with the exception of bugs) aspects can be assumed to be safe. In an untrusted public computing environment, new aspects cannot be assumed to come from a benign source.

• Modularising Web Services Management with AOP

• Relationship between Aspects

• Unraveling Crosscutting Concerns in Web Services Middleware• Monitoring

– PSL representation of service enactments has natural representation as a relational database

– Can use relational queries to perform run-time monitoring– Can use queries to do data mining on execution logs

• Transactions– Providing transactional guarantees remains largely open– What are the building blocks within services? In choreography?– Verifying transactional correctness?