ASPECT-MONITOR

An Aspect-based Approach to WS-contract Monitoring

Mario Freitas da Silva, Itana Maria de Souza Gimenes

Departamento de Informática, Universidade Estadual de Maringá, Av. Colombo, 5.790, Maringá, PR, Brazil

Marcelo Fantinato

Sistemas de Informação, Universidade de São Paulo, Rua Arlindo Béttio, 1.000, São Paulo, SP, Brazil

Maria Beatriz Felgar de Toledo

Instituto de Computação, Universidade Estadual de Campinas, Av. Albert Einstein, 1.251, Campinas, SP, Brazil

Alessandro Fabricio Garcia

Depto. de Informática, Pont. Univ. Católica do Rio de Janeiro, R. Marquês de São Vicente, 225, Rio de Janeiro, RJ, Brazil

Keywords: Electronic Contracts, Web services, Quality of Service, Aspects.

Abstract: Contract monitoring is carried out to ensure the Quality of Services (QoS) attributes and levels specified in

an electronic contract throughout a business process enactment. This paper proposes an approach to improve

QoS monitoring based on the aspect-oriented paradigm. Monitoring concerns are encapsulated into aspects

to be executed when specific process points are reached. Differently from other approaches, the proposed

solution requires no instrumentation, uses Web services standards, and provides an integrated infrastructure

for dealing with contract establishment and monitoring. Moreover, a Business Process Management

Execution Environment is designed to automatically support the interaction between customer, provider and

monitor organizations.

1 INTRODUCTION

Current business competition requires that

companies act quickly not to lose partnerships. The

internet, Business Process Management Systems

(BPMSs) (Weske, 2007) and Service-oriented

Computing (SOC) (Papazoglou et al., 2008) are

major resources towards improving inter-

organizational cooperation.

In the SOC paradigm, electronic services (e-

services) are part of distributed applications that

enable fast software development and cost reduction.

They are autonomous and platform independent

software that can be either atomic or composed from

lower granularity e-services. The Web services

technology, a realization of SOC, allows the

publication, search and discovery of e-service

according to internet standards (WSDL, SOAP and

UDDI). This technology has imposed additional

challenges to the BPM scope. Inter-organizational

cooperation requires proper regulation to ensure the

Quality of Service (QoS) exchanged between

collaborative partners (Fantinato et al., 2009).

Electronic contracts (e-contracts) are means to

represent an agreement between organizations in

such a way that they can be monitored throughout

the business process execution. E-contracts include

information about parties involved in a business

process, activities to be executed as e-services and

respective QoS and constraints. An e-contract life

cycle includes a negotiation phase that defines

contract parameters and an execution phase. In the

latter, the inter-organizational cooperation must be

monitored to ensure contractual clauses.

A reliable inter-organizational cooperation demands

e-contract monitoring. Contract conditions, such as

Freitas da Silva M., Maria de Souza Gimenes I., Fantinato M., Beatriz Felgar de Toledo M. and Fabricio Garcia A. (2010).

ASPECT-MONITOR - An Aspect-based Approach to WS-contract Monitoring.

In Proceedings of the 12th International Conference on Enterprise Information Systems - Software Agents and Internet Computing, pages 5-12

DOI: 10.5220/0002863800050012

 SciTePress

those related to QoS attributes, have to be constantly

and accurately supervised, for the benefit of every

party involved in the business process. E-contract

monitoring involves supervising the performance of

the provided services and collecting relevant

auditing information so that provider’s commitments

can be assessed and proper penalties can be applied

(Napagao et al., 2007).

Monitoring is not a trivial issue as it requires

process instrumentation either to register service

performance or to take corrective actions. The

aspect-oriented (AO) approach (Filman et al., 2005)

can be used to separate orthogonal concerns in the

BPM domain (Charfi and Mezini, 2004; Braem et

al., 2006). Concerns such as monitoring can be

encapsulated into aspects and executed when well-

defined point cuts are reached in the process.

Nevertheless, conventional aspect mechanisms

cannot be directly applied to contract monitoring.

This paper presents an AO approach to monitor

QoS attributes and levels, named Aspect-Monitor.

An e-contract comprises collaborative partners, an

inter-organizational business process specified in

AO4BPEL and QoS attributes of services in WS-

Agreement. Monitoring aspects are designed to deal

with Web services and their related QoS attributes

and levels. Thus, aspects are not only applied to the

process specification but also to enhance process

execution environment.

In this paper: Section 2 presents e-contracts and

monitoring; Section 3 discusses AO; Section 4

proposes an approach for e-contract monitoring;

Section 5 shows an example of application; Section

6 and 7 present lessons learned and related work;

and Section 8 concludes the paper.

2 ELECTRONIC CONTRACTS

Important e-contracts and monitoring concepts are

discussed in the following subsections.

2.1 Electronic Contracts

A contract is an agreement between two or more

parties interested in establishing a mutual

relationship on business or legal obligations. An e-

contract is an electronic document used to represent

an agreement between partners running business

using the internet (Erl et al., 2008).

Although e-contracts differ regarding their size,

content and complexity, there are usually common

elements within the same domain. The canonical

elements are (Grefen et al., 2001): parties

that

represent the organizations involved in a business

process; activities

that represent e-services to be

executed; and, contractual

clauses that describe

constraints on the execution of activities.

Contractual clauses can represent three types of

constraints: obligations

that describe what parties

should do; permissions that describe what parties are

allowed to do; and, prohibitions that describe what

parties should not do (Marjanovic and Milosevic,

2001). Obligations may include QoS clauses which

define attributes related to non-functional properties

of e-services. Examples are availability, integrity,

reliability, security, performance and reply time

(Keller and Ludwig, 2003; Menascé, 2002; Sahai et

al., 2002).

Different languages might be used to represent e-

contracts sections. The most recent ones are related

to Web standards. In this context, e-contracts are

called Web services e-contracts (WS-contracts). Our

approach focuses on WS-BPEL and WS-Agreement.

WS-BPEL has been widely used for business

process specification (Barreto et al., 2007). WS-

Agreement, based on WSLA (Keller and Ludwig,

2003), has been used for QoS specification.

2.2 Contract Monitoring

Contract monitoring requires events and information

produced by executing business processes. This

includes checking whether QoS attributes defined in

an e-contract are being obeyed during process

execution. Passive capabilities such as raising alerts

when a certain attribute is not according to specified

levels are not enough; therefore, corrective actions

must also be provided for running processes. Even,

contract renegotiation might be necessary. Thus,

monitoring goals, in the BPM domain, include not

only run-time measurement of QoS attributes and

KPIs (Key Performance Indicators) but also

dynamic adaptation to variation in parameters and

application of actions specified in contracts.

According to Benbernou et al. (2008), new

approaches developed for monitoring service-based

applications should come up with holistic and

comprehensive methodologies that:

1. Integrate various monitoring techniques at all

functional service-based application layers;

2. Provide a way to target all the relevant

application aspects and information;

3. Define rich and well-structured modeling and

specification languages capable of representing

these features;

4. Allow for modeling, identifying, and propagating

dependencies and effects of monitored events

ICEIS 2010 - 12th International Conference on Enterprise Information Systems

and information across various functional layers

and aspects in order to enable fault diagnosis.

Monitoring can be carried out by the consumer and

provider organizations, or else by a third-party.

Current approaches for e-contract specification used

for monitoring have an excess of instrumentation in

the process, many extra functions to be implemented

in the client and server and lack of available tools.

Our approach aims at reducing the complexity of the

e-contract monitoring mechanism by applying the

AO fundamental concepts. Moreover, it searches for

meeting the requirements set defined by Benbernou

et al. (2008) and presented above.

3 ASPECT-ORIENTATION

Systems are usually decomposed into modules to

reduce their complexity. The Structured and Object-

Oriented paradigms have been useful to provide

small units of reuse. However, they do not

adequately treat crosscutting concerns, such as

logging. The aspect-oriented (AO) paradigm aims at

encapsulating crosscutting concerns into isolated

parts of the system – called aspects, thus improving

development, maintenance and reuse (Filman et al.,

2005).

AO programming languages require specific

compilers. For example, the AJC compiler converts

an AspectJ program into a Java bytecode program,

which can be executed by any JVM. AO languages

have additional elements (Kiczales et al., 1997)

which include: aspect, join point, pointcut, advice

body and inter-type declaration.

AO4BPEL is a WS-BPEL extension which

introduces AO mechanisms to support e-service

composition (Charfi and Mezini, 2004). AO4BPEL

targets two existent problems in composition

languages: i) modularity specification allowing the

separation of concerns such as access control,

authentication and audit from business models; and,

ii) dynamic service composition. A specification in

AO4BPEL includes two main parts: a business

process in WS-BPEL and its respective aspects.

Aspects comprise PartnerLinks, Variables and

PointcutAndAdvice as illustrated in Figure 1.

PartnerLinks identify partners providing Web

services; Variables are used in the Advice part; and,

PointcutAndAdvice includes Pointcuts described in

Xpath and Advices in WS-BPEL. A Pointcut defines

the point in the process where an aspect should act.

Advices are executed when a Pointcut is identified.

Partner Links

Variables



PointcutAndAdvice



Pointcut



Advice



Figure 1: Aspects in AO4BPEL.

Our approach improves the application of the AO

paradigm to business process domain as it

complements AO4BPEL with the association of its

variables with QoS specified in WS-Agreement.

4 THE ASPECT-MONITOR

APPROACH

Aspect-Monitor proposes monitoring aspects as an

instance of the AO4BPEL aspects. In addition to be

related to the process, the new aspects are also

associated with QoS attributes and levels specified

in WS-Agreement. They are created to support the

monitoring of services to which they refer to.

This monitoring is part of a wider BPM approach

(Fantinato et al., 2009), including: business process

negotiation, reuse, contract establishment, dynamic

execution environment and the WS-contract

metamodel. In this paper, we focus on the

introduction of aspects concepts and the mechanisms

provided for supervising QoS attributes; no coverage

for aspect-orientation was provided in the previous

works already published by the same authors. Next

sections describe the BPM execution environment,

the introduction of aspects into the e-contract

metamodel and the monitoring mechanism designed.

4.1 The BPM Execution Environment

The execution of a business process and the

monitoring of its Web services require inter-

organizational cooperation and dynamic exchange of

e-services. Figure 2 presents the elements involved

in this execution environment comprising three

parties: Customer Organization; Provider

Organization; and, Monitor Organization (Fantinato

et al., 2009).

The Customer Organization has the most

complex structure, including: i) a structure for WS-

Contract Definition which supports WS-contract

negotiation and establishment; and, ii) a structure for

WS-Contract Execution to support the execution of

ASPECT-MONITOR - An Aspect-based Approach to WS-contract Monitoring

business processes specified in AO4BPEL. A SOC

System is necessary in the customer organization if

its own Web services are required as part of the

processes. In the Provider Organization, the SOC

System controls the Web services subcontracted by

the consumer.

Figure 2: Execution environment architecture.

The Monitor Organization implements the Aspect-

Monitor mechanisms. A third-party – the Monitor

Organization, has a WS-Contract Monitor structure

to control the execution of the process and hence the

composed Web services, by using a set of monitor

Web services and the QoS terms contained in the

WS-contract as a reference. These Monitor Web

services are invoked by the monitoring aspects

executed in the Customer Organization whenever a

join point is reached.

During the execution of a business process, the

customer organization invokes Web services which

can be local or subcontracted. For each invoked Web

service, a set of

Monitoring Aspects is triggered. The

aspects are related to QoS attributes defined to the

Web service. A monitoring aspect triggered during a

process execution invokes correspondent monitor

Web services, which will follow up the respective

services execution to ensure that the contracted QoS

levels are satisfied. If they are not satisfied, actions

can be undertaken according to the contractual

clauses. Those actions may be process cancellation,

penalty application and contract renegotiation.

A prototype for the WS-Contract Monitor

structure has been developed to support the

execution of Web services monitoring according to

the Aspect-Monitor approach.

4.2 WS-Contract Metamodel

A WS-contract metamodel represents rules to create

WS-contracts and supervise them based on aspects

(Figure 3). It includes concepts related to: i) Web

services described by the WSDL language; ii)

business processes involving Web services,

described by the business-part of the AO4BPEL

language; iii) QoS described by WS-Agreement

language; and, iv) monitoring aspects described by

the aspect-part of the AO4BPEL language.

A WS-contract is composed of four sections:

WSDL definitions, BPEL Business Process, WS-

Agreement, and Monitoring Aspects, as follows:

i) WSDL Definitions Section: contains the

primary elements Message Types, Partner Link

Types, Port Types and Operations - the last two

describe the Web services. These elements are

used to form the elements of the next sections;

ii) BPEL Business Process Section: describes

the business process that composes Web

services. It consists of: Variables, Partner

Links, Activities (both Interaction Activities

and Structured Activities types);

iii) WS-Agreement Section: describes the QoS

attributes and levels regarding the Web

services. Attributes and levels are described in

terms of: Service Properties (including

Variables) and Guarantee Terms (including

Service Scope and Service Level Objectives).

The WS-Agreement Name, Context and

Service Description Terms elements are not

included in this metamodel since there are

already similar sections representing this

information in the BPEL Business Process

section;

iv) Monitoring Aspects Section: contains the

aspects related to the Web services monitoring.

Each aspect is described in terms of:

Monitoring Partner Link, Monitoring Variable,

Join point, Pointcut and Advice.

Details about the first three sections are presented by

Fantinato et al. (2008). The fourth section is an

extension of the metamodel defined for the Aspect-

Monitor. The objectives of the Aspect elements as

well as their relationships with other WS-contract

elements are as follows:

 Monitoring Aspect: a module encapsulating a

monitoring crosscutting concern. It is composed

of monitoring partner link, monitoring variable,

pointcut and advice. There is a unique

monitoring aspect for each

Provider Organization Customer Organization

Monitor Organization

SOC Syste

Subcontracted

Web Services

SOC System

Own

Web Services

WS-Contract Definition

WS-Contracts

WS-Contract Execution

BPEL

Server

Monitoring

ects

WS-Contract

Monitor

QoS

Terms

Monitor

Web Services

Business

Process

ICEIS 2010 - 12th International Conference on Enterprise Information Systems

1 1

0..1

arent

0..1

WS-contract

AO4BPEL

definitions

WSDL

definitions

WS-Agreement

definitions

process

variable

process

partner link

partner

link type

port

type

structured

activity

service

property

guarantee

term

guarantee

variable

service level

objective

service

scope

interaction

activity

Aspect

definitions

monitoring

partner link

monitoring

variable

pointcut

advice

operation

monitoring

aspect

message

type

join point

0..1

Figure 3: WS-contract metamodel.

guaranteed variable and hence for each service

level objective, regarding the WS-Agreement

service properties and guarantee terms.

 Monitoring Partner Link: represents the

partners involved in the services monitoring,

which are: a monitoring organization; a

consumer organization; and, a provider

organization.

 Monitoring Variable: represents variables

related to the process in the advice element.

 Join Point: represents a Web service whose

execution must trigger a monitoring aspect,

thereby injecting behavior at the join point

through its advice body.

 Pointcut: represents the Operation which

identifies the Join Point – i.e. the Web service –

for which the monitoring aspect must react. In

this approach, the monitoring aspects have only

one join point for each pointcut.

 Advice: contains a business process, specified in

AO4BPEL, which must be executed when the

join point (Web service) triggers a pointcut. This

process must be used to invoke Monitoring Web

services. When a join point is reached, the advice

can be executed before, at the same time or after

the join point.

5 APPLICATION EXAMPLE

This section presents a practical experiment

undertaken on a pseudo-scenario to evaluate the

application of the Aspect-Monitor approach,

identifying its benefits and drawbacks.

The experiment context involves a travel agency

which uses Web services, from partner organizations

such as airline, car rental and hotel reservations

companies. Each party, in this collaborative business

process, provides a set of Web services to be used by

the other parties. The travel agency system offers

Web services to their customers which therefore

require Web services from its partners. A WS-

contract is established to regulate the business

agreement. An airline company can provide a series

of Web services to a travel agency, such as:

timetable queries, flight booking, ticket purchase,

itinerary changes and seat selection. On the other

hand, a travel agency can also provide some Web

services to the airline company, such as: customer

notification on flight changes and advertisement on

special offers.

As there is not, as yet, an AO4BPEL server

available, a WS-BPEL server – ActiveBPEL

(ActiveVOS, 2010) – was used instead; thus, a

workaround solution has been used, in the execution

environment, to execute aspect-related tasks.

Accordingly, the business process specified in WS-

BPEL (using here ActiveBPEL Designer) had to be

instrumented in order to manually enter in the

pointcuts the excerpt of process regarding the advice

to be executed. Thus, the business process receives

an instrumentation that simulates the use of aspects

which can be performed with the WS-BPEL

technology, using here the ActiveBPEL Engine.

Figures 4, 5, 6 and 7 present different excerpts of

the WS-contract in which the relationship between

Web services, business process, QoS attributes and

levels, and monitoring aspects can be observed. In

Figure 4, the Web service provided by the Airline

company (identified by the operation

flight-

bookingOP

) is defined.

ASPECT-MONITOR - An Aspect-based Approach to WS-contract Monitoring

<wsdl:portType name="flight-servicesPT">

...

<wsdl:operation name="flight-bookingOP">

<wsdl:input message="tns:flight-booking-Req"/>

<wsdl:output message="tns:flight-booking-Resp"/>

</wsdl:operation>

...

</wsdl:portType>

Figure 4: Excerpt from WSDL definitions.

In Figure 5, the invocation of the Web service is

specified in the WS-BPEL, identified by the

command invoke on the operation flight-bookingOP.

<bpel:invoke

partnerLink="flight-bookingPL"

portType=" flight-servicesPT"

operation="flight-bookingOP"

inputVariable="flight-booking-Request"

outputVariable="flight-booking-Response"/>

Figure 5: Excerpt from WS-BPEL definitions.

In Figure 6, a QoS attribute and its level are defined

for the Web service, identified respectively by the

reply-timeVAR and less than 60 seconds.

In Figure 7, the monitoring aspect related to the Web

service and QoS attribute is specified; when the Web

service whose operation is

flight-bookingOP is

invoked, the respective monitoring aspect is

triggered so that it can invoke a third-party monitor

Web service. The following elements are present:

the pointcut whose name is

book-flight-invoke is

defined for portType flight-servicesPT and operation

flight-bookingOP (Figure 4), which means that this

operation is the join point of this monitoring aspect;

and the advice, of “around” type, whose actions flow

is used to invoke the third-party monitoring Web

service, identified by portType

flight-services-

monitorPT

and operation flight-booking-monitorOP.

Since this monitoring aspect is related to the

reply-

timeVAR

, its content is copied to a temporary variable

so that it can be forward to the third-party

monitoring Web service to be invoked. Other

monitoring aspects for

flight-servicesOP regarding

other QoS attributes can exist as well as other ones

for

reply-timeVAR regarding other Web service

operation.

The monitoring aspects, producing the Aspect

definitions section, are generated semi-automatically

based on the information from the other WS-contract

sections: WSDL, WS-BPEL and WS-Agreement.

<wsag:ServiceProperties wsag:Name="flight-

bookingSP" wsag:ServiceName="flight-

bookingOP">

<wsag:VariableSet>

...

<wsag:Variable

wsag:Name="reply-timeVAR"

wsag:Metric="second">

<wsag:Location>//wsag:SDT/[

@portType="flight-bookingPT"

@operation="flight-bookingOP"]

</wsag:Location>

</wsag:Variable>

...

</wsag:VariableSet>

</wsag:ServiceProperties>

...

<wsag:ServiceScope ServiceName="flight-

bookingOP"/>

<wsag:QualifyingCondition>…</wsag:QualifyingC

ond…>

<wsag:ServiceLevelObjective>

<exp:Less>

<exp:Variable>reply-timeVAR</exp:Variable>

<exp:Value>60</exp:Value>

</exp:Less>

</wsag:ServiceLevelObjective>

<wsag:BusinessValueList>…</wsag:BusinessValue

List>

</wsag:GuaranteeTerm>

Figure 6: Excerpt from WS-Agreement definitions.

<pointcut name="book-flight-invoke"

contextCollection="true">

//process//invoke[

@portType="flight-servicesPT"

@operation="flight-bookingOP"]

</pointcut>

...

<bpws:sequence>

<bpws:assign>

<bpws:copy>

<bpws:from expression="reply-timeVAR"/>

<bpws:to variable="monitor-request"

part="service-property-namePART"/>

</bpws:copy>

...

</bpws:assign>

<bpws:invoke

partnerLink="third-party-monitoringPL"

portType="flight-services-monitorPT"

operation="flight-booking-monitorOP"

inputVariable="monitor-request"

outputVariable="monitor-response"/>

</bpws:sequence>

...

</advice>

</aspect>

Figure 7: Excerpt from Aspect definitions.

6 LESSONS LEARNED

This section presents the lessons learned from the

development and the exercising of the aspect-based

approach to WS-contract monitoring. In the

performed analysis, the proposed approach was

ICEIS 2010 - 12th International Conference on Enterprise Information Systems

compared mainly to the pure WSLA, WS-BPEL and

WS-Agreement approaches. Moreover, the

requirements presented by Benbernou et al. (2008)

for new approaches related to e-contract monitoring

were also taken into account.

No Need for Instrumentation. The proposed

approach allows the customer organization to define

its business process without adding extra code for

monitoring. It means that, according to the AO

paradigm, the main concern (i.e. the business

process) was not crosscut by the secondary concern

(i.e. the contract monitoring). Other monitoring

approaches do not perform such separation,

requiring instrumentation of the business process

with monitoring functions.

Simplified Computational Support. The proposed

approach simplifies the computational support

necessary to carry out e-contract monitoring when

compared to other existent approaches for the same

objective. No extra technology needs to be

implemented to support the monitoring functions.

The proposed BPM execution environment aims to

support all the contract life-cycle, including

monitoring, in a unique support environment.

Integrated Solution. The proposed approach

presents an integrated solution in which all the main

parts of a WS-contract are treated together: business

process, QoS attributes and levels, and monitoring

activities. Other monitoring approaches commonly

deal with isolated Web services and do not provide a

solution for composed Web services. This point is

closer related to requirements 1 and 2 from the set

proposed by Benbernou et al. (2008), since the

proposed approach provides a broad integration in

different levels – including different techniques and

information.

Use of Standard Languages. No new language was

defined to compose this approach. Instead, standard

languages, or already existing extensions, are used,

which together are capable of representing the

information related to contract monitoring, as

required by item 3 from the requirements set

proposed by Benbernou et al. (2008).

7 RELATED WORK

Several works are related to e-contract monitoring in

a general way, but not involving AO, from which we

can highlight Cremona (Ludwig et al., 2004) – used

as the architectural basis for the development of the

Aspect-Monitor approach. Cremona is an

architecture for the creation, management and

monitoring service-level agreements represented as

WS-Agreement documents. The monitoring module

is not only used to observe and detect contract

violations, but also to predict future violations and to

trigger corrective actions in advance.

There are also some aspect-based works related

to e-contract monitoring, but none of them applies

AO both in a wide and complete BPM approach, and

using specifically the WS-Agreement language as

presented in this paper. Some of these works are

presented as follows.

Singh et al. (2004) proposed a methodology

based on aspects to specify functional and non-

functional characteristics of Web Services. The Web

Services are described in an extended WSDL named

AO-WSDL and published in an extended registry

mechanism named AO-UDDI.

Tomaz et al. (2006) introduced AO concepts to

add non-functional requirements to Web services.

They focus on run-time adaptation of non-functional

characteristics of a composite Web service by

modifying the non-functional characteristics of its

component Web services. They also propose a

language for representing non-functional properties.

Ortiz & Leymann (2006) claim that, although the

encapsulation of non-functional services properties

using aspects are present in other works, aspect

implementation must be combined with WS-Policy

expressing non-functional properties. This proposal

maintains policies separated from the functional

behavior of the service and its main description.

Narendra et al. (2007) proposed run-time

adaptation of non-functional properties of a

composite Web service by modifying the non-

functional properties of its component Web services.

They use AO technology for specifying and relating

non-functional properties of the Web services as

aspects at both levels of component and

composition. WS-Policy and WSLA are used in the

negotiation between Web services.

Bianculli & Ghezzi (2007) proposed an approach

in which the behavior of a service is specified in an

algebraic language and can be checked at run-time.

A BPEL engine is extended, using AspectJ, with

three components: an interceptor, a specification

registry, and a monitor. The monitor is a wrapper for

the evaluation of algebraic specifications, which

keeps a machine-readable description of the state of

the process instances which is updated when the new

information from the interceptor is received. The

symbolic state is then evaluated and compared

against the expected one; and, in case of mismatch,

certain specific actions may be performed.

ASPECT-MONITOR - An Aspect-based Approach to WS-contract Monitoring

8 CONCLUSIONS

This paper presented an infrastructure to define,

execute and monitor WS-contracts. In the proposed

approach, a WS-contract comprises collaborative

partners, business process specified in AO4BPEL

and QoS attributes of services defined with WS-

Agreement. AO technology is used to separate

concerns such as monitoring into aspects. Those

aspects are executed when defined join point are

reached in the process. Compared to other

approaches, the proposed solution requires no

instrumentation, uses Web services standards and

provides an integrated infrastructure for dealing with

contract establishment and monitoring.

Future work includes: i) studying and

incorporating other AO properties to enrich the

proposed approach; ii) concluding the development

of the WS-Contract Monitor structure, from the

BPM execution environment; and, iii) carrying out a

broader experiment of the presented proposal to

evaluate its benefits and its limitations.

ACKNOWLEDGEMENTS

This work was supported by The State of São Paulo

Research Foundation (FAPESP) and The National

Council for Scientific and Technological

Development (CNPq), Brazil.

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