Applying Aspect Oriented Modelling to Service Orchestration

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Applying Aspect Oriented Modelling to Service
Orchestration

• Crest Centre, Kings 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
Advice
JoinPoint
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
BPEL Process
Aspect Definition
Aspect Deployment Description
Static Aspect Weaver

• Extract xsd from .bpel
• ltaspectgt.xml xsd
• Transformation Rules
• Locate pointcut
• Joint point merge
• Composing new .bpel

New BPEL Process Description
Standard BPEL Execution Environment
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Aspect Definition in XML
1 ltaspect name"Billing"gt 2 ltusinggt 3
ltnamespace name"xmlnsbill" uri"my.billing.uri"
/gt 4 ltpartnerLink name"billing"
partnerLinkType"billbillingLT" /gt 5
ltvariable name"billingMsg" type"billbillingMsg"
/gt 6 lt/usinggt 7 ltpointcut name"CallStarts(Jp)" 8
pointcut"invoking(Jp, CallService,
confCallPT, createConfCall)" /gt 9 ltpointcut
name"CallEnds(Jp)" 10 pointcut"invoking(Jp,
CallService, confCallPT, closeConfCall)"
/gt 11 ltadvice name"billService"gt 12 ltinvoke
partnerLink"billing" portType"billbillingPT" 13
operation"billService" inputVariable"billing
Msg" /gt 14 lt/advicegt 15 lt/aspectgt
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Service Implemented Aspect

• Definition of Service Implemented Aspects in
  WSDL

ltcomplexType name"EPmessage"gt ltallgt
ltelementname"opName" type"string"/gt ltelement
name"serviceType" type"string"/gt ltelement
name"serviceEndpoint type"EndpointReference"/gt
ltelement name"value" type"Serializable"/gt lt/a
llgt lt/complexTypegt ltmessage name"MessageReceived
"gt ltpart name"MsgReceived
type"tnsEPmessage"/gt lt/messagegt ltportType
name"EndPointMonitorPT"gt ltoperation
name"SendRequest"gt ltinput message"MessageSen
t"/gt lt/operationgt
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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 - BPELs 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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AOSD in WS Processes Infrastructural Concerns
choreography
. . .
Transformation
Aspect Interface
Transformation
orchestration
Presentation of Data
Aspect View Customised view of the System
Data
Internal service/API
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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?