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The automation of cross-organizational business processes bears great potential for companies to extend their market reach, save time, cut costs and respond to customer queries more agilely. However, technological support for the efficient organization of providing and consuming services across corporate boundaries is still not mature enough to allow for a large-scale adoption particularly among small-and medium-sized enterprises. In this article, we propose and evaluate different strategies with regard to architectures supporting the organization of service interconnections: In case of rather standardized and stable business relationships and interactions, a central service orchestration architecture, a hybrid orchestration approach with hub support and finally a fully decentralized peer-to-peer solution without any central control entity are proposed and compared in detail. In cases where business processes are highly complex, variable and dependent on situational factors, we propose a more implicit, declarative service orchestration methodology which builds upon Event-Driven Architectures (EDAs). For the different architectural strategies, we provide real-world exemplary implementations to prove their applicability and to investigate their strengths and weaknesses.
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SYSTEMATIC THOUGHT LEADERSHIP FOR INNOVATIVE BUSINESS
Paper Presentation
Christoph Schroth1 2, Till Janner1 2, Volker Hoyer1 2
Strategies for Cross-Organizational
Service Composition
1 University of St. Gallen, Institute for Media and Communications Management
{christoph.schroth, till.janner, volker.hoyer} @ {sap.com | unisg.ch}
2 SAP Research CEC St. Gallen, Switzerland
© SAP 2007 / Page 2
SAP Research Global Network
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Antipolis
Walldorf
Karlsruhe
Dresden
Belfast
Darmstadt
Campus-based Engineering Centers
SAP Labs-based Research Centers
planned
Zurich
St.Gallen
© SAP 2007 / Page 3
1. Executive Summary
2. Foundation and Related Work
3. Service Composition Decentralization Continuum
3.1. Central Orchestration
3.2. Decentral orchestration, hub supported
3.3. Decentral orchestration without hub
3.4. Evaluation Summary
4. Declarative Service Composition (Case Study Event-Bus Switzerland)
5. Conclusion and Outlook
Agenda
© SAP 2007 / Page 4
Executive Summary
Topics
and
Challenge
Web Service composition across company boundaries
Different strategies/ architecture possible
Method
and
Approach
Analysis of central, hybrid with hub support, and fully decentralized service
orchestration architectures
Evaluation and comparison on the basis of 8 criteria
Results
Service Composition decentralization continuum
Hybrid approach is most promising as it unifies the adavantages of both
centralized and decentralized solutions
Declarative Service Composition is needed in cases where processes are
not well standardarized or stable
© SAP 2007 / Page 5
1. Executive Summary
2. Foundation and Related Work
3. Service Composition Decentralization Continuum
3.1. Central Orchestration
3.2. Decentral orchestration, hub supported
3.3. Decentral orchestration without hub
3.4. Evaluation Summary
4. Declarative Service Composition (Case Study Event-Bus Switzerland)
5. Conclusion and Outlook
Agenda
© SAP 2007 / Page 6
Automatization of Cross-Organizational
Business Transaction
Drivers and Benefits Hurdles of Adoption
!
Improvements of cost-
performance ratio of IT
Extending market reach
Saving time
Cutting costs
Responding to customer
demands more agilely
Different standards and
standardization approaches
prevent from a common
understanding of business
processes and data
High costs and complexity of
existing approaches
SOA aims at
closing this gap
© SAP 2007 / Page 7
Orchestration vs. Choreography
Orchestration Choreography
vs.
Represents the relation between
one central service and different
other ones called according to a
pre-defined sequence
Adequate to describe exchange
patterns of one individual service
Can be conducted with the help of
languages such as BPEL
Executable on respective engines
Bird‘s eye view
Message exchange described from
the perspective of an observer who
is able to see all interaction of the
participants of a choreography
Languages, e.g. WS-CDL, BPSS
Not executable, used for modelling
and monitoring
Modelling the overall choreography and
derive executable orchestrations
© SAP 2007 / Page 8
Orchestration vs. Choreography
Example
Transform Send PO
Retrieve PO
Ack
Rec PO
Response Transform
From
ERP
To ERP
Receive PO Transform
Send PO
Ack
Transform Send PO
Response
From
ERP
To ERP
PO Request
PO Request Ack
PO Response
Choreography
Orchestration
Buyer Seller
© SAP 2007 / Page 9
Example Business Process
© SAP 2007 / Page 10
1. Executive Summary
2. Foundation and Related Work
3. Service Composition Decentralization Continuum
3.1. Central Orchestration
3.2. Decentral orchestration, hub supported
3.3. Decentral orchestration without hub
3.4. Evaluation Summary
4. Declarative Service Composition (Case Study Event-Bus Switzerland)
5. Conclusion and Outlook
Agenda
© SAP 2007 / Page 11
Central Service Orchestration
BPEL
Engine
Stakeholder A
Application
Collaborative
Modeling
Data & Process
Templates
Application Application
Service Interface
User
Registry
BPEL
Generator
Adapter Adapter Adapter
Stakeholder B Stakeholder C
Server
Con
Invocation policies (not all
services might be called by one
single hub)
Lack of trust
Single point of failure
Pro
Efficient monitoring
Fault handling
Maintenance
Less local complexity
© SAP 2007 / Page 12
Decentral Service Orchestration with Hub
Support
BPEL
Engine
Stakeholder A
Application
Collaborative
Modeling
Data & Process
Templates
Application Application
Service
Interface
User
Registry
BPEL
Generator
Adapter Adapter Adapter
Stakeholder B Stakeholder C
Server
BPEL
Engine
BPEL
Engine
Derived BPEL
Peer Process
Con
Fault handling more complex
Users must be able to handle an
execution engine
Increased complexity
Pro
Message exchange independent
from server
Overall choreography can still be
used for monitoring and fault
handling support
© SAP 2007 / Page 13
Decentral Orchestration without Hub
BPEL
Engine
Stakeholder A
Application Application Application
Service
Interface
Adapter Adapter Adapter
Stakeholder B Stakeholder C
BPEL
Engine
BPEL
Engine
User Registry
Templates
Modeling
BPEL Generator
User Registry
Templates
Modeling
BPEL Generator
User Registry
Templates
Modeling
BPEL Generator
Derived BPEL
Peer Process
Sync Sync
Con
Permanent synchronization of
the local repositories
Complicated fault handling
Highest complexity on client side
Pro
Robustness against partial errors
Higher scalability
© SAP 2007 / Page 14
Evaluation Summary
© SAP 2007 / Page 15
1. Executive Summary
2. Foundation and Related Work
3. Service Composition Decentralization Continuum
3.1. Central Orchestration
3.2. Decentral orchestration, hub supported
3.3. Decentral orchestration without hub
3.4. Evaluation Summary
4. Declarative Service Composition (Case Study Event-Bus Switzerland)
5. Conclusion and Outlook
Agenda
© SAP 2007 / Page 16
Declarative Service Organization
Architecture Style: Event-Driven Architecture (EDAs)
Conceptual extension of the principles of SOA
Communication patterns (one-way notification, request/ response, notification, confirmation,
etc.)
Central communication layer (Event-Bus)
Three major components
Event-Bus
Middleware module
Takes over institutional funcationality (message formats, routing information formats,
security, reliability)
Adapters
Ensure connectivity and interoperability
Coordination Services
Finite state-machines (FSMs) are used to describe the behavior of even-driven services
© SAP 2007 / Page 17
Case Study: Event-Bus Switzerland (EBS)
Event-Bus Switzerland (EBS)
Sub-Bus
S S S S EBS Services
Directory Services
Sub-Bus
S S S S
Sub-Bus
S S S S
Sub-Bus
S S S S
Virtu
al E
BS
Event/ Catalogue services
Transformation Services
SecurityServices
Operating Services
Tracing Services
Abo Services
Error Services
Exception Services
Validation Services
Routing Services
Special Services
Munici-
pality
External
Stakeholder
State
Canton
SP
SP
SP
SP
ES
ES
ES
ES
© SAP 2007 / Page 18
1. Executive Summary
2. Foundation and Related Work
3. Service Composition Decentralization Continuum
3.1. Central Orchestration
3.2. Decentral orchestration, hub supported
3.3. Decentral orchestration without hub
3.4. Evaluation Summary
4. Declarative Service Composition (Case Study Event-Bus Switzerland)
5. Conclusion and Outlook
Agenda
© SAP 2007 / Page 19
Conclusion and Outlook
3 different stategies for service composition across company
boundaries where analyzed.
Comparison and evaluation on the basis of 8 criteria
The hybrid approach is the most promising strategy within the service
composition decentralization continuum
Declarative Service Composition is needed in cases where processes
are not well standardized or stable
Prototypical realization in different research projects ongoing (EU
funded project GENESIS, Swiss national funded project HERA).
