COMPONENT-ORIENTED MODEL-BASED WEB SERVICE

ORCHESTRATION

Suela Berisha, Jacques Hamalian and Béatrice Rumpler

Université de Lyon, CNRS, INSA-Lyon, LIRIS, UMR5205 F-6962, Villeurbanne, France

Keywords: Service Oriented Architecture (SOA), Web Services Orchestration (WSO), Service Modelling, UML

Modelling, Model-driven Architecture (MDA), Service Component Architecture (SCA).

Abstract: The Web service orchestration enables cross departmental coordination of business processes in a

heterogeneous environment. We have designed a component-oriented web service orchestration based on

service functionality in an Enterprise Service Bus (ESB). Our orchestration model is centralized-based,

where a single service is the central coordinator containing the composition logic of the other services

involved. These services are modelled using Service Component Architecture (SCA) specification, defined

in our UML profile described in this paper. SCA conforms to SOA (Service Oriented Architecture)

principles using CBSE (Component-Based Software Engineering) techniques. Finally, our specified

orchestration model is implemented using Model-Driven Architecture Approach (MDA).

1 INTRODUCTION CONTEXT

The Information System (IS) of the SNCF

(http://sncf.com/en_EN/flash/#/CH0001/BR0959/) is

based on a complex data exchange system with,

heterogeneous, distinct and very large data sources.

So, it becomes very difficult to get the “good”

information or data according to a user need,

rapidly. The introduction of Service-Oriented

Architecture (SOA) (Papazoglou & al. 2007),

(Pautasso & al. 2008), whose main component is the

Web Service (WS), promises a better organization

on the global system and enhances more the

visibility of the business process, according to a

standard-based service orchestration. However, this

type of architecture presents new problems because

services constitute a set of consequent “moving

parts” not knowing each other. Moreover, in the case

of dysfunction, the task of identifying the problem

becomes very difficult, and searching the error costs

a lot. Therefore, it is necessary to implement a

general politic for a system in order to manage and

supervise services and their life-cycle, integrated in

a global Web Service Orchestration (WSO).

Currently, there exist some implementation works

regarding this type of infrastructure. However, at the

moment, these works don’t enough convince

managers to be proposed at the company level.

Our work places this problem area in an

empirical case study about the “human resource

domain”. First, we have proposed the architectural

model of a platform based on ESB infrastructure

(Chappel 2004), (Schmidt & al. 2005). This model

contains a meta-model layer and a model layer based

on a service orchestration engine, a service interface

and three types of repositories: process repository,

event repository and service repository (Hamalian

2009). This paper presents the following steps: (i)

the proposition of a conceptual orchestration model

and (ii) the procedure for an implementation and (iii)

the results obtained from the conceptual model.

2 FUNDAMENTAL CONCEPTS

AND MODELLING

APPROCHES

WSO implies three fundamental concepts: (i) the

orchestration model (Joffroy & al. 2007), (Ortiz &

al. DC 2006), (ii) the business processes and (iii) the

implementation languages (Panagiotis 2008).

An orchestration model is an interaction model

that takes place during the construction of composed

web services. This orchestration is based on some

requirements (Ivanova 2006) and criteria (Dustdar &

al. 2005), (Erradi & al. 2005) concerning web

service composition, like: modularity (Chappel

2004), capacity of communication and coordination

(Dustdar 2005), incremental approach to service

479

Berisha S., Hamalian J. and Rumpler B. (2010).

COMPONENT-ORIENTED MODEL-BASED WEB SERVICE ORCHESTRATION.

In Proceedings of the 12th International Conference on Enterprise Information Systems - Information Systems Analysis and Speciﬁcation, pages

479-482

DOI: 10.5220/0002908204790482

 SciTePress

composition and modelling (Gronmo & al. 2004).

We have taken account of these criteria during our

model designing.

Business processes are integration programs that

tie together various entities within (and between)

organizations, to achieve business goals. They are

ideally suited to be implemented in a Service

Oriented Architecture (SOA), where functionality is

provided by services with well-defined interfaces

(Papazoglou & al. 2007). The service orchestration,

make profit of the POM (Process-Oriented

Modelling) and aims to describe the sequence of

activities involved in a business process. These

sequences are designed graphically thanks to

modelling tools (by business actors) or specified in a

formal language (by programmers).

Currently, some formal orchestration languages

(Ivanova 2006) are based on programming

languages, for example: JSR207 and jPD. But they

are limited in terms of interoperability and

reusability. Thus, the most available are derivation

of XML which try to model business processes

interpreting WSDL Files (Web Service’s Interface).

Indeed, each service represents a business specific

function and a set of services form a business

process. For example BPEL (or BPEL4WS) design

composite service applications that need some

process logic. It is a system-to-system process well

adapted for well known process structures. We have

chosen BPEL4WS for his interoperability and

reusability capacities, but it can’t deal with

processes only formed at run-time, without

modelling patterns. It requires from the designer to

be aware of the sequence logic between the different

activities involved prior to designing the

orchestration model. So, we are interested in

modelling approaches that might occur patterns.

The first, the SCA (Ortiz & al. 2006) is a CBSE

(Bernd 2008) specification providing the

composition and the aggregation logic of services

according to the system functionalities, i.e. business

process logic. It provides methods and concepts to

create components and to describe how they can

work together. SCA has sharply gaining acceptance

in the services-oriented industries because it offers

some advantages like understandability,

maintainability, reusability, composability,

capability in reconfiguration. But SCA doesn’t

integrate the remaining development stages (Ortiz &

al. DC 2006), neither the sequence activities logic,

that can be defined separately, using UML sequence

diagrams for each possible business activity. For the

complete automatic development system from and to

end, we have chosen the meta-model of MDA

approach (Nasser 2005) (Ortiz & al. 2006), (Ivanova

2006), (Pham & al. 2007). This model leads us to

distinguish a Platform-Independent Model (PIM)

where we find the business logic and the

functionalities, and a Platform-Specific Model

(PSM) which represents a specific model for an

implementation technology or an execution

platform.

3 CONCEPTUAL MODEL

According to the architectural model (Hamalian

2009) and MDA recommendation we have designed

a Conceptual model (Figure 1) showing coordination

between layers, repositories and execution platform.

Event repository

(EDA)

Service repository

(SOA)

Meta model

[ UML + SCA specification ]

(PIM)

Event

Business Processes repository

(PIM)

Orchestration model

(PIM)

(PSM)

Code (XML-BPEL)

Business &

Functional

Level

Technical

Level

Execution Engine

(BPEL)

Execution

platform

Trigger

Constructs

Transformed into

Figure 1: Our conceptual model according to MDA.

Services could be activated by events which are

defined in the event repository according to Event-

Driven Architecture (EDA) (Papazoglou & al. 2007)

in an SOA. We have combined SCA with MDA in a

PIM model: the business and functional layer. UML

became the foundation modelling language in

OMG’s MDA and then, we represent SCA

specification using UML 2 component diagram. The

next step transforms the PIM model based on MOF

into an XML document (PSM model) via XMI.

Moreover, our PSM model contains the SCA

specification defined in XML. Since we have a

model conformed to MOF, we can use any MOF-

based frameworks or tools. This permits us to ensure

the interoperability between the systems by the help

of an exchange file which contains the mapping

rules between MOF-XMI. Next, the PSM model is

transformed into BPEL code that describes our

orchestration model which contains the SCA

specification.

ICEIS 2010 - 12th International Conference on Enterprise Information Systems

480

Figure 2: Our orchestration PIM model combined with the UML profile for SCA.

4 THE IMPLEMENTATION

We propose to build an orchestration model based

on where the service implementation is encapsulated

in the form of a black box and its functionalities are

exposed via input/output interfaces using the SCA

specification (Ortiz & al. 2006). (Masmoudi & al.

2006) had represented a correspondence between

UML 2 component models and its equivalent in

BPEL, in order to model aggregate software

components using the UML. However, the

difference, with respect to our work is that, he didn’t

envisaged the “mapping” between SCA and BPEL

which permits us to obtain a better modularity and

adaptability for our system. These mappings are

represented in the Table 1 and the Table 2.

After having defined these correspondences, we

have built our orchestration PIM model combined

with the UML profile for SCA (Figure 3).

So, the service component is now stereotyped as

<<SCA_Component>>. It supplies its interface

“I_InitialisationRecrutement” through the port

“P_IR” stereotyped as <<Service>> which could be

used by other services. Moreover, it provides a

reference for other services through the interface

“I_Resultat” and through the port “P_IR_Resultat”

stereotyped as <<Reference>>. Similarly, other

service components are stereotyped as

<<SCA_Component>> providing their services

through interfaces by the help of their corresponding

ports stereotyped as <<Service>>. The connection

between two components is specified through a

dependency connector which is stereotyped as

Table 1: “Mapping” proposition between SCA and BPEL.

SCA BPEL4WS

Component PartnerLink(<partnerLinks>)

Composite PartnerLink

System Assembly Process

(<process/>)

Components

Invocation

Sequence of activities (<sequence/>)

Reference Reply

Service Invoke, receive

Wire Service components interaction logic

Property Variable

Implementation

Web Service’s Implementation

corresponding to a partnerLink

BPEL Process (exposed as a WSDL Service Type)

BPEL Process (corresponding to the final system)

Table 2: Our “mapping” proposition between SCA and

UML 2 component diagram.

SCA UML 2 component diagram

Component Component

Composite Composite component

System Assembly Artefact

Components Invocation

Sequence diagram between the

involved components

Reference Port (Required Service)

Service Port (Supplied Service)

Wire Dependency

Property Property

Implementation

Service Implementation of a

component

<<Wire>> following the SCA specification. For

simplification, the property stereotype is not shown

in Figure 2. In order to implement the new UML

Profile for SCA, we have defined a sequence of

operations using a UML sequence diagram.

(Hamalian J 2009). The implementation of our

COMPONENT-ORIENTED MODEL-BASED WEB SERVICE ORCHESTRATION

481

orchestration model is formalized by the way of a

XML file containing the BPEL source code

(Hamalian S 2009). This BPEL process is interfaced

as a WSDL file that could be consumed as web

services in other functional contexts.

5 CONCLUSIONS AND FUTURE

WORK

In this paper we have proposed a web service

orchestration model following the SCA specification

which takes into account elementary service

aggregation and service design regarding the

business perimeter. We consider that a specific actor

can define an elementary service adapted to a

functional task or an activity of its business. This

service can be combined with other services

(elementary or composite) to be adapted to an

activity granularity or a business process. In order to

implement this type of aggregation, we have built

the UML service profile model which extends the

UML actual metamodel for taking into account the

characteristics of an SCA component.

At the moment, we work at the implementation

of a system able to reuse the BPEL file source code

in a larger scale of framework, compared to this

prototype. In terms of further perspective we

propose to work on the integration of the Aspect-

Oriented Modelling (AOM) approach in the current

models for taking into account technical transversal

tasks shared by many business processes

(identification, authentication, service class

management, etc.).

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