AN ONTOLOGY MANAGEMENT TOOL FOR QOS-BASED WEB

SERVICES DESIGN

Marco Comerio, Flavio De Paoli and Gianluigi Viscusi

Universit

a di Milano-Bicocca, via Bicocca degli Arcimboldi 8, 20126 Milano, Italy

Keywords:

Web services, Ontology, Qualities of Service (QoS), Value perspective, Web Service Design Tool.

Abstract:

Web Services are the current most promising technology based on the concept of Service Oriented Computing

that provides the basis for the development and execution of business processes that are distributed over the

network and available via standard interfaces and protocols. Quality of Services (QoS) represents a major

issue that covers the challenges in the service composition area and in the service oriented engineering. In this

paper, we present the Web Services Design Tool (WSDTool). This tool allows the different actors involved in

Web services design to deﬁne and address QoS requirements.

1 INTRODUCTION

Web Services are the current most promising technol-

ogy to make business processes accessible inside and

across organizational boundaries (Papazoglou, 2003;

Khalaf et al., 2006; Leymann et al., 2002). The in-

creasing availability of Web services that offer similar

functionalities underlines the need to augment service

descriptions with a well-deﬁned set of non-functional

properties (NFP) and, in particular, of qualities of ser-

vice (QoS). In fact, even if a service fulﬁls all of

its functional requirements by providing the required

features, it can still be unacceptable if, for example,

availability is too little, performance is too poor, or

usability does not meet user expectations.

Functional aspects deal with system behavior and

its features. Non-functional requirements deal with a

large number of quite different types of requirements.

Some of those have been deeply analyzed, such as se-

curity (e.g., safety, privacy, and authentication), per-

formance (e.g., throughput, response-time, jitter, and

scheduling) and dependability (e.g., availability, reli-

ability, and robustness). Others, such as usability and

adaptability, are more complex to deﬁne and measure.

QoS is grounded in the value system in which

service provision and composition are involved. In

fact, it is related to the improvement of business

perspectives in service design. According to the

Service-Oriented Computing roadmap (Papazoglou

et al., 2006), such a perspective represents a ma-

jor issue that covers the challenges (i) in the ser-

vice composition area (QoS-aware service composi-

tions and Business-driven automated compositions),

and (ii) service-oriented engineering, by focusing on

the real world grounding of the services and on user-

driven design. The latter is important to involve the

different stakeholders of an organization (e.g. man-

agers, business modelers, service designers, etc.) in

the design activity.

In this paper, we present the Web Services Design

Tool (WSDTool) that allows the different actors in-

volved in the design of a Web service to deal with

quality requirements. WSDTool provides a graphi-

cal interface aiming at supporting ontologies manage-

ment and modeling activities. The tool was designed

to primarily guide the execution of the Web Service

Modeling Design (WSMoD) methodology.

The WSMoD approach consists in incorporating

and reﬁning NFP, as well as functional requirements,

along the design process. The advantage of managing

NFP is twofold: achieving at the end of the process,

a ready-to-implement speciﬁcation, and reducing the

risk of delivering unsatisfactory services.

WSMoD makes use of ontologies to understand,

discover, classify and reason on NFPs that are re-

lated to user constraints, user preferences, technolog-

234

Comerio M., De Paoli F. and Viscusi G. (2007).

AN ONTOLOGY MANAGEMENT TOOL FOR QOS-BASED WEB SERVICES DESIGN.

In Proceedings of the Third International Conference on Web Information Systems and Technologies - Web Interfaces and Applications, pages 234-239

DOI: 10.5220/0001279602340239

 SciTePress

ical features (such as devices and networks), and do-

main characteristics. Ontologies provide a formal or-

ganization of knowledge that is exploited to rational-

ize decision and evaluation processes. In the current

version, we refer to a set of ontologies that were de-

veloped in the MAIS project (Pernici, 2006; Comerio

et al., 2007). These ontologies provide a description,

classiﬁcation and characterization of services, context

(user and channel characteristics) and QoS.

The methodology is composed of ﬁve main

phases. The Service Identiﬁcation phase speciﬁes,

from a business point of view, the features the service

will offer, and the business constraints. This phase

delivers a complete, informal speciﬁcation of func-

tional and non-functional requirements. The func-

tional requirements are the input of the Service Mod-

eling phase, which has the goal of deﬁning the func-

tional model of the Web Service. The non-functional

requirements and the functional model are inputs of

the High-Level Re-Design phase, whose goal is to re-

vise, and possibly change, the functional model to in-

clude non-functional requirements. The next phase,

Customization, revises the current design model by

considering a possible context of execution. Finally,

the Web Service Description phase translates func-

tional model into standard WSDL interfaces aug-

mented with quality descriptions in WSOL (Tosic

et al., 2002). In this paper, only the phases dealing

with NFP aspects are considered. For a complete de-

scription of WSMoD, the reader can refer to (Comerio

et al., 2007).

The paper is organized as follows: Section 2 mo-

tivates the introduction of a value perspective in the

Web service design and discusses the QoS issue in the

area of the Service-Oriented Computing. Section 3

outlines WSDTool characteristics and functionalities.

Section 4 illustrates the use of WSDTool during the

design process. Finally, Section 5 draws conclusions

and presents future works.

2 VALUE PERSPECTIVES ON

QOS-BASED WEB SERVICES

DESIGN

In business interactions, a major issue consists in en-

hancing the business perspective over service provi-

sion, by developing strategies and tools that provide

support in the selection of services according to busi-

ness goals and processes.

In such a scenario, a major challenge is to under-

stand and make explicit the bind of services to busi-

ness processes from a value perspective; this knowl-

edge allows the creation of representations that can

be exploited to evaluate the competitive advantage of

services according to strategic models, such as the

value-chain model (Porter, 1985).

The Service Oriented Computing paradigm is

centered on the relevance of business modeling for

service design and development (Papazoglou et al.,

2000). The analysis of different business models cre-

ates a shared understanding of how business oper-

ates and what kind of services are needed to sup-

port a given process at a given time. Value-based

approaches to Semantic Web Services (Akkermans

et al., 2004) point out the importance of modeling ser-

vices that are grounded in the real world. These ap-

proaches are supported by a value-based perspective

on requirements and engineering (Gordijn and Akker-

mans, 2003), which enhances the relevance of busi-

ness models in service design. The focus on busi-

ness models identiﬁes different layers of service de-

sign, which span from the business domain, where

a service has an outcome, to the technological layer

that concerns the implementation of the Web service.

In each domain, such different layers need a sharable

representation of the involved objects and concepts to

make the relations between them accountable at dif-

ferent levels. Furthermore, since a service scenario

usually involves different organizations, representa-

tions of business domain and implemented Web ser-

vices are needed.

Besides sharable representation of business ob-

jects and business processes, integrated value systems

(Papazoglou et al., 2000) need representations of the

qualities of service that are requested by the actors

involved in the business interaction. These quality is-

sues enhance, according to the business criteria, the

value of a service and improve composition across or-

ganizational boundaries.

At the state of art, ontologies (Guarino, 1998) are

the most suitable way to provide a common represen-

tation of different domains of an organization, and to

support the interactions among organizations. A dis-

cussion on ontologies in the business domain can be

found in (Gailly and Poels, 2005). To express the po-

tentiality of ontologies, let’s consider, for example,

the scenario in which an agent is engaged in a process

to ﬁnd a location for a new point of sales. The agent

has to communicate the results of the data-collect ac-

tivity to the actors that are involved in the strategic

management to let them verify whether a location ﬁts

certain requirements. This information can be sent

via different delivery channels according to the re-

ceiver’s preferences and available channels (e.g., PC

with Internet connection or cellular phone). An on-

tology can help to support the process; in facts, a ser-

AN ONTOLOGY MANAGEMENT TOOL FOR QOS-BASED WEB SERVICES DESIGN

235

vice needs a semantic representation of the involved

elements, such as delivery channels, organizational

functions (e.g., the management levels and roles), and

types of message required (e.g., unstructured e-mail,

structured data for data base and warehouse).

To the best of our knowledge, the one presented

in this paper is an original effort to combine these

research topics to provide, at design level, an inte-

grated view on the linkage of services to business

processes through a value-chain perspective (Barone

et al., 2006).

The approach is to supply suitable representations

of QoSs to software designers, which develop the

Web services, and to business actors, which (i), as

clients, ask for services that are compliant with their

value activities and (ii), as providers, want to supply

services augmented with rich information about valu-

able qualities associated with their services. In fact,

a major issues in business transactions is the business

commitment (Papazoglou et al., 2000), which is the

result of an agreement between business parties; such

a commitment is based on a contract (implicit or ex-

plicit) where the qualities of services are key factors.

This model should drive the deﬁnition of an ontol-

ogy of qualities to deliver a tool that can be exploited

in different phases of a service life-cycle. In this con-

text a critical issue deals with the wide range of prop-

erties that can characterized a QoS (Cappiello et al.,

2004). The WSDTool makes use of an ontology that

includes complete descriptions of quality concepts -

and their relations- to manage non-functional issues

during the design process. Back to the process of

searching a location for a new point of sales described

above, a ﬂexible QoS-based Web Service for message

notiﬁcation need to be developed. In Section 4, the

design of FlexSend, a delivery service over different

channels, will be discussed as a case study that illus-

trates how WSDTool uses the formal organization of

knowledge provided by the ontology of qualities to

rationalize and improve the design process.

3 THE WEB SERVICES DESIGN

TOOL (WSDTOOL)

The main objective of the WSDTool is to support the

design of a Web service that involves persons with

different roles and skills: business experts, domain

experts and software designers. Each of these cate-

gories is supplied with suitable interfaces and interac-

tion. For example, the interaction with business ex-

perts, which are often unfamiliar with technology and

tools, should be made as easier and straightforward as

possible by user-friendly editors and tailored presen-

tations. On the contrary, the interaction with software

designers includes more technical interfaces.

The need of creating different perspectives and

views inﬂuenced our decision to implement the tool as

an Eclipse plug-in (Eclipse, 2005) . Eclipse provides

the Plug-in Development Environment (PDE) for cre-

ating plug-ins and integrating them with the Eclipse

Platform. The possibility to edit views, wizards and

editors makes PDE very effective for the development

of WSDTool features.

To link the different activities performed by the

different actors, ontologies are used as gluing tools. In

fact, on one side, they establish a common vocabulary

and a repository of information that guide the whole

design process. On the other side they collect and or-

ganize the semantic associated with the designed ser-

vices.

To support the execution of the WSMoD method-

ology, WSDTool provides for the following features:

• Ontology Management: import, Navigation and

Editing of ontologies. In particular, the tool

allows the browsing of the ontology concepts

(classes, properties, relations and instances)

though an advanced 3D graphical interface.

• Service Modeling: management of UML dia-

grams to develop models of Web services.

• NFP-aware Modeling: integration of the func-

tional model with the non-functional model of a

Web service via graphical manipulation.

• QoS Evaluation: guided evaluation of QoS

through graphical interface.

• Web Service Description: translation of UML di-

agrams into WSDL and WSOL documents.

Ontology visualization is based on OntoSphere3D

that was chosen for its simple and user-friendly nav-

igation facilities (OntoSphere3D, 2006). The ap-

proach, described in (Bosca et al., 2005), follows two

different principles: (i) increase the number of “di-

mensions” (colors, shapes, transparency, etc.) which

represent concepts features; (ii) automatically select

which part of the Knowledge Base has to be displayed

and the level of detail that has to be used in the pro-

cess, on the base of user direct manipulation of the

scene (rotation, panning, zoom, object selection, etc.)

WSDTool provides three different perspectives

(one for each user role) composed of different views:

• Main view: composed of four different panels: the

3D viewer panel for 3D representation of ontolo-

gies; the Relation viewer panel for 3D visualiza-

tion of relations between concepts or instances;

the New service editor panel for editing functional

and non-functional requirements; ﬁnally, the QoS

evaluation panel for evaluating of QoS.

WEBIST 2007 - International Conference on Web Information Systems and Technologies

236

Figure 1: Discovery a category for FlexSend.

• Tree view: a 2D-tree representation of the ontolo-

gies to search for concepts, by Keyword search ac-

tion, and to create new instances of services, by

New service action.

• Property view: a visualization of the properties of

a selected concept or instance to access the quality

evaluation features, by QoS evaluation action.

• Modeling view: to create UML diagrams from a

list of requirements and speciﬁc UML proﬁles.

• Web Service Description view: to automatically

create WSDL and WSOL descriptions.

4 WEB SERVICES DESIGN WITH

WSDTOOL

To illustrate the features of WSDTool, the design

of a Web service with the WSMoD methodology is

discussed. In particular, the Service Identiﬁcation

and the Customization phases that mostly involve the

quality issues are examined in detail. As a case study,

the design of a notiﬁcation service, FlexSend, that de-

livers messages over different channels according to

speciﬁc receivers contexts (preferences, device, activ-

ity) is considered.

The Service Identiﬁcation phase delivers a com-

plete speciﬁcation of functional and non-functional

requirements from the business point of view. The

work starts with the deﬁnition of the FlexSend func-

tional requirements and the creation of a UML use-

cases diagram. Then, the phase proceeds with the

identiﬁcation of the category of FlexSend by creat-

ing a new instance in the service ontology. WSD-

Tool supports this activity in two ways. In a way,

the user makes use of the keyword search action to

search for categories that are described with particular

keywords. In the FlexSend running case, specifying

”message” as keyword, one of the obtained categories

is Message Delivery Service. The selection of this cat-

egory triggers the visualization of its properties in tree

view, property view and main view.

In the other way, the user browses the service on-

tology with the 3D viewer and the relation viewer to

identify the best category and create the new instance.

As shown in Fig.1, WSDTool supports the browsing

of ontologies by highlighting the elements of interest

while leaving out the others. In a given scene, every

concept is clickable with two different results: a right

click permits the visualization of all the concept in-

stances; a left click navigates through elements main-

taining the current perspective. Starting from a global

view, a left click on the Internet Service concept deter-

mines the scene illustrated in Fig.1. From this scene,

it is possible to select the FlexSend category (Message

Delivery Service), click on it and obtain the relative

properties in the properties view. In particular, WSD-

Tool allows the user to see that each service included

in the Message Delivery Service category is charac-

terized by a set of QoS (e.g., Service Availability and

Service Usability) and it is inﬂuenced by the network

and the device on which it is delivered.

Figure 2: New Service Editor.

After service categorization, the business expert

investigates the availability of existing services that

satisfy part of the FlexSend requirements to reuse

them in the new service. This operation can be per-

formed by examining instances of the selected cate-

gory, either through the tree view (concept instances

are visualized as leaves of the tree and marked with

the label “I”) or through the 3D viewer (spheres repre-

senting a concept with at least one instance are char-

acterized by a transparent “halo”). Fig.1 shows that

no instances are available, so the design of a com-

AN ONTOLOGY MANAGEMENT TOOL FOR QOS-BASED WEB SERVICES DESIGN

237

pletely new service is required. The invocation of

new service action activates the new service editor.

Fig.2 illustrate what the business expert sees when

“FlexSend” is inserted as name of the new service.

FlexSend is an instance of Message Delivery Service

so it inherits all the qualities visualized in the “Has

Quality” list. The business expert can change this

QoS list by removing or adding new quality require-

ments. For each quality in the list, WSDTool visual-

ize the related QoS-tree that is created using the de-

pendency relations among qualities speciﬁed in the

ontology. Fig.2 shows a Service Performance QoS-

tree in which each quality is labeled as “To be Calcu-

lated” meaning that a process of quality evaluation is

needed.

The next step is the identiﬁcation of the inﬂuences

of context characteristics. A Message Delivery Ser-

vice is inﬂuenced by the type of network and device

on which messages will be delivered. So, the busi-

ness expert speciﬁes the conceptual devices and net-

works (i.e. high-level speciﬁcation without techno-

logical details) that can be used by the ﬁnal users to

interact with FlexSend. As shown in Fig.2, concep-

tual devices for the FlexSend service are PC and Cel-

lular Phone, while conceptual networks are GPRS and

UMTS.

After requirement deﬁnition, the FlexSend de-

sign proceeds with the others phases of the WSMoD

methodology. For space reason, we omit to report

details related to Service Modeling and High-level

Redesign phases, so to focus on the Customization

phase, which is an innovative feature of the tool. The

objective is to illustrate how the non-functional re-

quirements are evaluated considering channel proﬁles

concerning real devices, network interfaces, networks

and application protocols that providers can exploit

for service provisioning. As an example, the evalua-

tion of the Service Performance quality requirement

is discussed. Fig.3 shows that the considered quality

is affected by others, therefore, it must be evaluated

by the composition rules that characterize the quality.

The evaluation process starts with the selection of

a channel conﬁguration. In our example, this opera-

tion consists in the selection of instances of network

and device. Technical characteristics of the available

conﬁgurations are reported in technical characteris-

tics list (e.g., Network Transmission Time = 0.8 msec,

Network Delay = 200 msec etc ). The example in

Fig.3 shows the evaluation of Service Performance

with the following channel conﬁguration: Cellular

phone with GPRS. The applied composition rule (an

algorithm in this case) is the one associated with the

quality in the ontology:

1. Evaluate Network Adaptivity using the Tuple

Figure 3: QoS Evaluation Editor.

method;

2. Evaluate Device Reconﬁgurability using the Tuple

method;

3. Evaluate Service Flexibility using the Simple Ad-

ditive Weighting (SAW) technique;

4. Evaluate Service Execution Time using the Aver-

age method;

5. Complete the process evaluating Service Perfor-

mance using the SAW technique.

For space reason, we omit the description of meth-

ods and techniques involved in Service Performance

evaluation. The reader can refer to (Ardagna et al.,

2005) for a detailed description.

The evaluation of the required qualities in the ac-

tual environment supports the validation of the de-

signing service. The service requirements deﬁne

thresholds that the service needs to meet or overcome

(for simplicity, proportional quality dimensions are

considered, i.e. the higher value the better quality).

The chosen conﬁguration can meet the thresholds but

others conﬁgurations can provide insufﬁcient values.

Considering these results the business expert can de-

cide to re-negotiate business QoS constraints or to re-

vise the Web service design.

5 CONCLUSIONS AND FUTURE

WORKS

In this paper, we have presented the Web Services

Design Tool (WSDTool) that supports the WSMoD

methodology, an ontology-based approach to address

QoS issues in the design process of Web services. An

innovative features that clearly distinguish WSDTool

from other design IDE is the management of QoS

WEBIST 2007 - International Conference on Web Information Systems and Technologies

238

representations that cover different perspectives, from

business to technical.

The business perspective covers the challenges in

QoS-aware service compositions, business-driven au-

tomated compositions and service-oriented engineer-

ing by focusing on the real world grounding of ser-

vices and on user-centered design. This approach is

important to involve the actual stakeholders in the de-

sign activity.

The development of WSDTool is an ongoing

work. The current version provides a partial imple-

mentation of Tree view, Property view and the Main

view. Future works deal with the completion of the

WSDTool with the implementation of Modeling view

and Web Service Description view. To create the Mod-

eling view, we are evaluating the integration of stan-

dard UML 2.0 plug-ins (e.g., Eclipse UML Studio

(Omondo, 2006)). Concerning the creation of the

Web Service Description view, we are working in two

directions: one concerning the creation of a WSDL

and WSOL-oriented UML proﬁle for the automatic

creation of Web service descriptions in WSDL and

WSOL; the other concerning the selection of available

tools that support the required translation. Currently,

we are evaluating UMT (UMT, 2006), a tool that pro-

vides for model transformation and code generation

based on UML models in the form of XMI.

ACKNOWLEDGEMENTS

The work presented in this paper has been partially

supported by the European IST project n. 27347

SEEMP - Single European Employment Market-

Place and the Italian FIRB project RBNE05XYPW

NeP4B - Networked Peers for Business.

REFERENCES

Akkermans, H., Baida, Z., Gordijn, J., Pena, N., Altuna, A.,

and Laresgoiti, I. (2004). Value webs: Using ontolo-

gies to bundle real-world services. IEEE Intelligent

Systems, 19(4):57–66.

Ardagna, D., Comerio, M., DePaoli, F., and Grega, S.

(2005). An hybrid approach to qos evaluation.

In EMMSAD ’05: Proceedings of the International

Workshop on Exploring Modeling Methods in Systems

Analysis and Design, pages 581–592, Porto, Portugal.

Barone, D., Viscusi, G., Batini, C., and Naggar, P. (2006).

A Repository of Services for the Government to Busi-

nesses relationship. In NGITS ’06: Proceeding of the

Next Generation Information Technologies and Sys-

tems, Kibbutz Shefayim,Israel.

Bosca, A., Bonino, D., and Pellegrino, P. (2005). Onto-

sphere: more than a 3d ontology visualization tool. In

SWAP ’05: Proceedings of the Semantic Web Applica-

tions and Perspectives Workshop, Trento, Italy.

Cappiello, C., Missier, P., Pernici, B., Plebani, P., and Ba-

tini, C. (2004). Qos in multichannel is: The mais ap-

proach. In ICWE Workshops ’04: Proceedings of the

International Conference on Web Engineering, pages

255–268, Munich, Germany.

Comerio, M., DePaoli, F., Grega, S., Maurino, A., and Ba-

tini, C. (2007). Wsmod: A methodology for qos-based

web services design. International Journal of Web

Services Research.

Eclipse (2005). Eclipse platform technical

overview. Technical report, Available at:

http://www.eclipse.org/articles/whitepaper-platform-

3.1/eclipse-platform-whitepaper.html.

Gailly, F. and Poels, G. (2005). Towards an OWL-

formalization of the resource event agent business do-

main ontology. Technical report, ISWC 2005 - OPSW

workshop.

Gordijn, J. and Akkermans, J. M. (2003). Value-based

requirements engineering: exploring innovative e-

commerce ideas. Requir. Eng., 8(2):114–134.

Guarino, N., editor (Amsterdam, 1998). Formal ontologies

and information systems. IOS Press.

Khalaf, R., Keller, A., and Leymann, F. (2006). Business

processes for web services: Principles and applica-

tions. IBM Systems Journal, 45(2):425–446.

Leymann, F., Roller, D., and Schmidt, M.-T. (2002). Web

services and business process management. IBM Sys-

tems Journal, 41(2):198–211.

Omondo (2006). Eclipse UML Studio. Available at:

www.omondo.com.

OntoSphere3D (2006). OntoSphere3D. Available at:

http://sourceforge.net/projects/ontosphere3d.

Papazoglou, M., Traverso, P., Dustdar, S., Leymann, F., and

amer, B. (2006). Service-oriented computing: A

research roadmap. In Service Oriented Computing

(SOC), number 05462.

Papazoglou, M. P. (2003). Web services and business trans-

actions. World Wide Web, 6(1):49–91.

Papazoglou, M. P., Ribbers, P., and Tsalgatidou, A. (2000).

Integrated value chains and their implications from a

business and technology standpoint. Decis. Support

Syst., 29(4):323–342.

Pernici, B. (2006). Mobile Information Systems. Infras-

tructure and Design for Adaptivity and Flexibility (the

MAIS approach). Springer.

Porter, M. E. (1985). Competitive Advantage. The Free

Press, New York.

Tosic, V., Patel, K., and Pagurek, B. (2002). Wsol - web ser-

vice offerings language. In CAiSE ’02/ WES ’02: Re-

vised Papers from the International Workshop on Web

Services, E-Business, and the Semantic Web, pages

57–67, London, UK. Springer-Verlag.

UMT (2006). UML Model Transformation Tool. Available

at: http//umt-qvt.sourceforge.net.

AN ONTOLOGY MANAGEMENT TOOL FOR QOS-BASED WEB SERVICES DESIGN

239