A Formal Model of Business Application Integration from Web Services (Position Paper) Authors: Kaiyu...

A Formal Model of Business Application Integration

from Web Services

(Position Paper)

Authors:Kaiyu Wan: East China Normal University, Shanghai, China.

Mubarak Mohammad Concordia University, Montreal, Canada.

Vasu Alagar: X’ian Jiaotong-Liverpool University, Suzhou, China.

SOFSEM 2009Špindlerův Mlýn, Czech Republic

Agenda

• Service-Oriented Architecture• Proposal• Abstract Model• Service Creation Fascility Process• Example

Wan, Mohammad, and Alagar - SOFSEM 09 2

Service Oriented Architecture

3Wan, Mohammad, and Alagar - SOFSEM 09

Service ProvidersSP1

SP2

SP3

Business ProcessModel

Service Consumers (Requesters)SR1

SR2Business Goal

Building software by composing services allows companies to collaborate together to execute business processes.

Challenges


State user requirements.State user requirements.

Find services.Find services.

Compose services.Compose services.

Deliver services.Deliver services.

How to state user requirements?

How to translate user requirementsInto service specifications?

How to automatically matchUser requirements with service profiles?

How to ensure that services are trustworthy?

How to ensure that non-functionalrequirements are preserved in composition?

How to ensure that policies are respected?

How to compose services automatically toprovide business transactions?

Proposal

• An intelligent automation factory:– translate user requirements into service

specifications,– match making skills,– compose web services to accomplish the business

process requirement, and– maintain non-functional requirements and policies.

• Providing formal foundation to support the method.


Abstract Model


Service Presentation Layer(SPL)

Service Presentation Layer(SPL)

Service Request Layer(SRL)Service Requirements

Specification

Non-Functional Requirements

ConstraintsAnd Obligations

Service Delivery(Deployment)

Formal Validation ofConfigurationOptimal Configuration

Service ConfigurationGenerator

Service CompositionGenerator

Service Creation Facility (SCF)

Characteristics of SCF• Autonomy• Task assessment• Service discovery• Service qualification• Candidate selection• Candidate composition• Composition qualification• Optimality• Self monitoring


Service Presentation Layer (SPL)


SPLS1 S2 Sn

Syntax for interface type Si isSemantic:Extended-Timed Automata, Ai

Fi : I(Si) O(Si)

where I(Si) is the typed argument list ,

and O(Si) is the typed output of the

service Fi.


SPL_instanceS11 S12 S13 S21

S23

SPL_templateS1

S2

The interface behavior of this SPL instance can be written as:

F1 + F2

A1 * A2

Trustworthy Component Type*


DataData

ServicesServices

InterfacesInterfaces

PropertiesProperties

ConstraintsConstraints

AvailabilityAvailability

TimelinessTimeliness

SafetySafety

SecuritySecurity

ReliabilityReliability

Pre/Post ConditionsPre/Post Conditions ArchitectureArchitecture

ConnectorConnector

ConfigurationConfiguration

Functional Contract Structure

* Mohammad and Alagar. TADL - An Architecture Description Language for Trustworthy Component-Based Systems. ECSA 2008.

Service Request Layer (SRL)

• A service is a functionality to be constrained by certain quality attributes.

• Service requests are formalized as requirements.

• The request for service should include:– Functionality– Non-functional (quality of service attributes)– Obligations– Policies


Formalizing Service Requests


SRL

SCF_I1 SCF_I2 SCF_In

UML Sequence Diagram

First-Order Logic Expressions

E1 E2 E3 Non-Functional RequirementsObligationsPolicies and resource constraints

ServicesDocument TypesHow services interact and document types flow

SCF Process Model


RequestTransform UML into

Chore Expressions

Chore Expressions

Match Chore

Expressions with the services

Candidate services

Check non-functional

requirementsTrusted services

Compose Services

and check optimality

Optimal configuration

Apply policies and obligations

SRL

SPLSCF

1. From Sequence Diagram to Chore Expressions

• The sequence diagram consists of entities, message sequences, and data parameters for messages.

• We transform:– Messages into tasks (services).– Data parameters are associated with tasks.– Relations among messages into composite

operators with tasks as operands.


Chore Expressions• The semantics of a sequence diagram are precisely expressed by the semantics

assigned to chore expressions.• Sequential composition: a>>b

– After a is completed, its output may be used by b.

• Parallel composition: a||b– Simultaneous execution of a and b with no data sharing.

• Composition with no order (and): a o b– Conjoined evaluation with no order, order is not important.– It is possible to share data– The result is the set of results produced by the evaluation of a and b

• Nondeterministic choice (or): a ∫ b– One of the actions is evaluated nondeterministically.

• Priority Construct: a ◊ b– a is evaluated first, and if it can be successfully completed, then b is discarded;

otherwise, b should be evaluated (order).• Commit Construct: com(e)

– The state changes that happened during the evaluation of expression e are made permanent.


2. Matching Services with Requests• A chore expression may require investigating

more than one sequence of actions against services (e.g., choice or priority operators)

• Example: a ∫ (b ◊ c)– Consider both : a ∫ b and a ∫ c– Determine the matching service sequence.– Reject an expression only if its corresponding service

sequence does not satisfy the non functional properties.

– If both sequences satisfy the stated non-functional properties, then both should be examined for optimality criteria.


3. Algorithm for constructing Chore service Expressions


do

Choose an expression f from He

doChoose the next action a in f (left to right)do

Choose a service provider P in SPL

Determine the service interface x in P whose signature matches the argumentsand their types in a

Substitute the arguments for interface signature parameters and check the satisfaction of precondition of the interface function sa

Execute the behavior at the interface

If the outcome satisfies the post-condition of the interface function then accept The service sa; replace a by sa in f

If any of the previous steps fail then Exit

Forever PForever a

Put f in Se

Forever f

1.

2.

3.

4.

5.

6.

7.

8.

9.

• We assume that SCF uses an ontology to match user specific task names with the service names at the interfaces.

• The SCF passes either the service names or the display name, from the profile of each service, to the SRL.


Service Configuration Templates• Construct a configuration template from a chore expression.


• a >> b || c


4. Checking Optimality

• The service configurations that satisfy the contract specification are selected for further processing.

• Based upon an optimality criteria, an optimal service configuration can be obtained.

• Examples of optimality criteria include:– minimizing the total cost of service delivery – minimizing the execution time – maximizing the reliability of a service configuration.


Example: Travel planning

• Book a round trip flight ticket and stay at a four star hotel, rent a car, and make an appointment with a friend at specific place and time.

• There are four SPLs, one for each service:– Airline reservation– Hotel booking– Care rental– Appointment arranging.


Sequence Diagram


Airline SPL


Flight Schedules Current Booking

Ticketing

Payment Center

Pricing

PoliciesBookingCenter

PFP PFTPFE

SCF

PT

CF

PP

Behavior Specification


Service Configuration


( (t1 >> t2) || (t3 >> t4) || (t5 >> t6) || (t7 >> t8) ) >> t9 || t10 || t11 || t12

Conclusion

• In order that the SCF be trusted, it should accept only the services from a platform that itself is certified to be trustworthy.

• We are developing tools and methods to build a framework for the development of trustworthy services for the SPL.

• The role of context awareness.


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