Download - FLACOS Malta October 2008
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FLACOS Malta October 2008
Service Oriented Architectures: The new Software Paradigm
W. Reisig
Humboldt-Universität zu Berlin
Theory of Programming
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Service Oriented Architectures: The new Software Paradigm
I Some General Remarks
II Some First Assumptions for a Formal Framework
III A Modelling Technique for Services
IV A small Case Study
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Service Oriented Architectures: The new Software Paradigm
I Some General Remarks
II Some First Assumptions for a Formal Framework
III A Modelling Technique for Services
IV A small Case Study
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Voices on SOA from the software industry
“THE most relevant emerging paradigm”
“A substantial change of view as it happens at most once each decade”
“The next fundamental software revolution after OO”
“Much more than just an other type of software!”
“The foundational layer for tomorrow's information systems”
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The paradigm of SOA- is intended to couple encapsulated software components
("services"),
- supports flexibility and convenience of interaction.
- has very pragmatic sources and backgrounds: - Business process technology, - Web service technology.
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Current Practice of SOA- equips business processes
with web-based communication facilities.
- is influencing - Enterprise Application Integration, - Software Engineering, - Systems Management, - Data provisioning, - BPI, - B2B.
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Languages and Modelling TechniquesWS- BPEL,
Business Process Modelling Notation (BPMN),
YAWL,
ADEPT,
UML -ACT,
Petri Nets,
…
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The future of SOApursues more ambitious goals: - modularization, proper interfaces, standardization for enterprise computing and enterprise application integration.
- applies SOA in contexts other than web services and business processes. e.g. wireless networks
- spawn SOA as a new paradigm of computing.
- requires a theoretical basis for SOA, independent from implementations.
i.e.
mathematic
al models
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What is so fundamentally new?
classical theory:A computing system computes functions.
9 -1
25
moderate interest
in the environment
3 5 not terminating
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the idea of “service”
a new kind of system:
fundamentally new aspects:
- infinite runs are sensible
- environment is not trivial,
deserves its own attention,
should be described formally.
How?
! Just as the system itself !
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problems to be addressed by models- Service Composition, orchestrations and
choreographies:
! disambiguate these notions !
- Semantics of services:
… specified in a given modelling language
! A service may not be intended to be implemented !
- Expressive power of modelling languages:
Idea: … relative to the bare minimum of expressive power needed to specify services.
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problems to be addressed by models- Substitutability of services: Replace S by T … also during execution of S.
- Brokering: Which information about processes should the broker
know?
- Reliability and Correctness: Verification, at varying levels of rigour.
- Design Methodology: Methods and principles of Software Engineering must be adapted to SOA.
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Service Oriented Architectures: The new Software Paradigm
I Some General Remarks
II Some First Assumptions for a Formal Framework
III A Modelling Technique for Services
IV A small Case Study
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Service CompositionLet S denote the set of all services.
Services are made to be composed.
a ticket machine and a client
Two composed services behave like one service
purchase =def ticket machine and client
formally: : S S S purchase =def ticket machine client
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Semantics of a serviceA (composed) service may regularly terminate.
ticket or money back
irregular: ticket machine crashes
formally: a "beauty" predicate, i.e. a subset S.
In most cases, is weak termination.
Def. Let R, S S.R is a partner of S iff R S sem(S) =def the set of all partners of S.
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Equivalence of servicesR is at most as comprehensive as S (written R<S)
iff each partner of R is a partner of S.
formally: R < S iff sem(R) sem(S).
Consequently, two services are equivalent, R S,
iff R < S and R < S.
Apparently:
Two systems are equivalent
whenever their environment can not distinguish them.
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Quests at the partners of a service, S
• Is R a partner of S ?• Does S have partners at all ? • Is there a canonical partner of S ?• How characterize all partners of S ?
Controllability
Composability
“most liberal”Operating Guideline
we offer implemented analysis techniques for all of them
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Quests at the substitution of S’ for S
• Can S’ substitute S ?• Is there a public view of S ?
• Given R and S : Construct T
such that R is a partner of ST
SubstitutionNormal form
adapter generation
that‘s what we are doing right now
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Service Oriented Architectures: The new Software Paradigm
I Some General Remarks
II Some First Assumptions for a Formal Framework
III A Modelling Technique for Services
IV A small Case Study
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coin
tea!
coffee!
beverage
coin
coffee!
beverage
Toy example: a vending machine
the coffee partner:
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Beauty predicate: Proper termination
coin
beverage
with no tokens left on the interface
coin
tea!
coffee!
beverage
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coin
tea!
beverage
Another partnerthe tea partner:
coin
tea!
coffee!
beverage
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coin
tea!
coffee!
beverage
coin
tea!
coffee!
beverage
Are there more partners?
the coffee-or-tea partner:
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coin
tea!
coffee!
beverage
First coffee! then coin
coin
coffee!
beverage
Swap the order
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coin
tea!
coffee!
beverage
coin
tea!
coffee!
beverage
Three independent threads of control
This is the most permissive partner:
Each other partner can be derived from this one.
no sequential control
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coin
tea!
coffee!
beverage
coin
tea!
coffee!
beverage
characterize the set of all partners by help of this one
This is the most permissive partner:
Each other partner can be derived from this one.
operating guideline
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Petri Nets …
the mst generic modelling technique for services
offers the bare minimum to express yourself
good to verify properties and for canonical constructs
! translate your pet language into Petri nets
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Service Oriented Architectures: The new Software Paradigm
I Some General Remarks
II Some First Assumptions for a Formal Framework
III A Modelling Technique for Services
IV A small Case Study
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Case Study: BPEL Online Shop
yes no
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open net,generated by BPEL2oWFN
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automatically generated
partner
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the operating guideline
one moreinterleaving
inscriptions
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Modified Shop
yes no
decision notcommunicated!
has no partners at all
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FLACOS Malta October 2008
Service Oriented Architectures: The new Software Paradigm
W. Reisig
Humboldt-Universität zu Berlin
Theory of Programming
the
end