Orriëns, B.

Papazoglou, M.

Yang, J.

English

Research Papers in Economics

ServiceCom: A Tool for Service Composition Reuse and Specialization 
 
Bart Orriëns, Jian Yang and Mike P. Papazoglou 
Tilburg University, Infolab, PO Box 90153, 5000 LIE, Tilburg Netherlands 
{b.orriens, jian, mikep}@uvt.nl 
 
 
Abstract 
 
Web services are becoming the dominant paradigm for 
distributed computing and electronic business. This has 
raised  the  opportunity  for  service  providers  and 
application developers to create value added services by 
combining web services. Several web service composition 
solutions have been proposed, e.g. BPEL4WS. However, 
these  approaches  are  either  not  flexible  or  too 
complicated as they lack proper support for modularity 
and  reusability.  Motivated  by  the  demand  of  a  light-
weighted  tool  of  service  composition,  we  developed 
ServiceCom, a tool for service composition specification, 
construction and execution. In this paper we discuss how 
ServiceCom  suppors  reusable  web  service  composition 
specification, combination, and execution. 
 
 
1. Introduction 
 
Web  services  are  self-contained,  internet-enabled 
applications  capable  not  only  of  performing  business 
activities on their own, but also possessing the ability to 
engage  other  web  services  in  order  to  complete  higher 
order business transactions. The platform neutral nature of 
the  web  services  creates  the  opportunity  for  building 
composite  services  by  using  existing  elementary  or 
complex services possibly offered by different enterprises. 
For  example,  a  travel  plan  service  can  be 
developed by combining several elementary services such 
as hotel reservation, ticket booking, car 
rental,  sightseeing  package,  etc.,  based  on 
their WSDL descriptions. By composite service, we mean 
a service that uses other services. The services that are 
used  by  a  composite  service  are  called  its  constituent 
services.  Web  service  design  and  composition  is  a 
distributed  programming  activity.  It  requires  software 
engineering principles and technology support for service 
specification, reuse, specialization, and extension such as  
those  used,  for  example,  in  component  based  software 
development. Normally composite services are developed 
by hard-coding business logic into application programs. 
the development of business applications would be greatly 
facilitated if methodologies and tools for supporting the 
development and delivery of composite services in a  
 
 
coordinated and effectively reusable manner were to be 
devised.  Some preliminary work has been conducted in 
the  area  of  service  composition,  mostly  in  aspects  of 
business process modeling language [2] and composition 
specification  e.g.  BPEL4WS  [3].  However,  these 
approaches are either not flexible or too complicated as 
they lack proper support for modularity and reusability. 
Motivated  by  the  demand  of  a  light-weighted  tool  of 
service  composition,  we  developed  ServiceCom,  a  tool 
for  service  composition  specification,  construction  and 
execution.  In  this  paper  we  provide  an  overview  of 
ServiceCom, and outline its significance and contributions 
to the research in service composition. 
 
2. Overview 
 
ServiceCom  is  a  Java  based  tool  for  modular  and 
reusable web service composition. The tool is based on 
the  concept  of  service  component  [7], which facilitates 
the idea of web service component reuse, specialization 
and  extension.  Service  components  are  a  packaging 
mechanism  for  developing  web-based  distributed 
applications  in  terms  of  combining  existing  (published) 
web services. Service components have a recursive nature 
in that they can be composed of published web services 
while in turn they are also considered to be themselves 
web services (albeit complex in nature). Once a service 
component is defined, it can be reused, specialized, and 
extended. 
To  support  the  service  component  mechanism  a 
Service  Composition  Specification  Language  (SCSL) 
has  been  developed  (see  [7]  for  the  syntax).  In  this 
language activity, binding, condition and composition type 
constructs are used (among others) to define a web service 
composition.  Activity  constructs  represent  constituent 
services  through  the  use  of  name  and  description 
characteristics. To bind activities to particular web service 
providers  binding constructs can be attached to activity 
constructs. These bindings identify an operation on a port 
of  a  service  in  the  WSDL  interface  of  the  provider. 
Alternatively, they may provide search criteria to enable 
the  locating  of  appropriate  providers  during  runtime. 
Condition constructs may be used in case of conditional 
compositions to govern the control flow within the service component.  To  express  different  forms  of  activity 
choreographies  SCSL  utilizes  the  composition  type 
construct.  Supported  types  include  If,  IfElse, 
ParaWithSync,  ParaAlt,  SeqAlt,  SeqNoInt,  SeqWithInt 
and WhileDo patterns.  
Based on top of the service component mechanism and 
SCSL  ServiceCom  propagates  a  phased  approach  to 
service  composition  spanning  composition  description, 
planning,  building  and  invocation.  An  overview  of  this 
phased approach is provided in Figure 1. In the following 
we  briefly  describe  the  purpose  of  the  Description, 
Planning,  Building  and  Invocation  phase  and  discuss 
how ServiceCom implements each phase. We also explain 
how reuse, extension and specialization are supported. 
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2.1. Description phase 
 
In  the  Description  phase  users  can  specify  a  web 
service composition. For this purpose ServiceCom offers 
a composition designer, which provides a visual-oriented 
development  environment.  First  a  composition  type  is 
selected.  Subsequently  activity,  binding  and  condition 
constructs may be dragged and dropped on the designer 
window. Characteristics may be set and edited through the 
use of popup dialogs, which can be opened by double-
clicking a composition construct. Alternatively, constructs 
may be inserted, edited and removed through the use of 
menus.  A  screenshot  of  the  composition  designer  is 
provided in Figure 2 in Appendix A. 
Reuse, extension and specialization of constructs in the 
Description phase is based upon the use of unique names 
and  namespaces.  This  combination  ensures  that  a 
reference  to  a  construct  may  only  refer  to  a  single 
construct, since a construct name must be unique within a 
namespace and each composition has a unique namespace. 
For the reuse of constructs simple references can be used.  
Extension and specialization is supported through the 
utilization of base types. When specifying a base type for 
a construct the characteristics of this base construct are 
inherited by the sub-construct. Additional information in 
the sub-construct not present in the base construct extends 
the base construct. Similarly, in case of information that is 
present  in  both  the  sub  and  base  construct  the 
characteristics  of  the  base  construct  are  overridden.  In 
ServiceCom both references and base types can be made 
through the selection of composition constructs from the 
web  service  composition  library.  (See  Figure  4  in 
Appendix A for a screenshot) 
 
2.2. Planning phase 
 
The  Planning  phase  is  concerned  with  binding  the 
activities in the service composition to concrete services. 
For  this  purpose  ServiceCom  offers  a  web  service 
provider  library  facility.  This  library  facility  contains 
locally known web service providers, which can aid the 
user in case he does not know an appropriate provider for 
an activity in a composition. (i.e. the WSDL interfaces are 
stored on the local system). Web service providers may be 
added and removed from the library. Also, a search on the 
Internet  can  be  performed  to  locate  suitable  providers, 
based  on  user-specified  search  criteria.  Any  located 
providers may then be added to the library, making them 
locally available. Furthermore, provider functionality may 
be tested through a quick invocation. As such, the web 
service provider library is of great help in the planning 
phase of the web service process model by enabling the 
reuse of web service providers. For a screenshot of the 
library see Figure 3 in Appendix A. 
In  case  a  user  does  not  want  to  search  and  select  a 
service  provider  manually  ServiceCom  is  capable  of 
selecting  appropriate  providers  automatically  during 
runtime.  For  this  purpose  the  tool  utilizes  the  search 
criteria specified in the binding construct(s). 
 
2.3. Building phase 
 
The Building phase is of essence in the web service 
composition  phase  model.  It  crosses  the  gap  between 
composition  specification  and  actual  invocation.  In  this 
phase the web service composition specification is used as 
input  to  generate  the  set  of  Java  source  and  class  files 
required for the invocation of the composition. This set of 
files comprise of the following: 
 
·  Firstly, for each activity in the composition a set of 
Java source and class files is created for invocation. 
These files are derived from the WSDL definition of 
the  service  provider,  specified  in  the  binding 
construct  of  the  activity.  For  each  service  in  the definition a class is defined, as well as for the ports of 
these  services.  Operations  are  represented  as  Java 
methods, whereas faults are expressed as exceptions. 
Additionally,  files  are  generated  that  translate 
operation invocations from and to SOAP messages to 
enable XML-based invocation. 
·  Secondly,  a  set  of  Java  source  and  class  files  is 
created for the web service composition. These files 
enable  the  invocation  of  the  composition  in  the 
specified  manner.  The  exact  types  of  files  that  are 
generated depend on the type of the composition. For 
example, if a composition is of the type if, then its 
condition constructs are mapped to source and class 
files.  In  case  of  parallel  compositions  source  and 
class files are generated that enable the invocation of 
an activity in a separate thread of execution. 
·  Thirdly, a WSDL definition is generated for the web 
service composition. This definition functions as the 
public interface of the composition. 
·  Fourthly,  the  composition  is  stored  as  a  SCSL 
specification to enable further reuse 
 
The above files can all be reused in the composition 
building  process.  Firstly  ServiceCom will only generate 
source and class files for a composition if they are not 
already in the library. For example, suppose a service is 
involved in multiple compositions, instead of generating 
new files for each composition only one set files will be 
generated and it will be reused in all other compositions 
this service is involved in.  
Secondly,  generated  files  can  be  used  in  the 
development  of  other  applications.  The  mentioned 
functionality  may  be  extended  and  specialized  in  an 
object-oriented fashion through the use of Java overriding 
and inheritance mechanisms. However, these two types of 
reuse  are  in  our  opinion  best  facilitated  in  professional 
programming environments and are thus considered to be 
outside the scope of ServiceCom. 
Thirdly, reuse of the generated public interface of the 
composition  is  possible.  The  WSDL  definition  may  be 
included  in  the  web  service  provider  library,  making  it 
available for use in other compositions. The interface file 
can also be published in for example an UDDI registry to 
make the composite service’s functionality known to the 
outside world. For the latter purpose ServiceCom offers a 
deploy  mechanism.  This  mechanism  enables  the 
publication of the new, composite web service in standard 
web service containers, such as Tomcat and J2EE.  
 
2.3. Invocation phase 
 
The Invocation phase deals with the execution of a web 
service composition and its corresponding result handling. 
In  most  cases  users  will  likely  want  to  incorporate  the 
composition’s functionality in custom made programs. In 
these  situations  the  development  of  nice,  user-friendly 
interfaces  are  left  to  the  designers  of  these  programs. 
However,  some  users  may  simply  want  to  invoke  the 
service  once  and  are  not  interested  at  all  in  software 
program  development.  These  users  may  employ  the 
standard  interfaces  for  the  web  service  composition, 
which  can  be  generated  prior  to  invocation.  Although 
these interfaces are basic, they provide a means to the user 
to  enter  the  required  inputs  and  display  the  received 
outputs.  These  interfaces  can  be  reused  in  a  similar 
fashion as the Java source and class files generated in the 
Building phase.  
 
3. Demo 
 
We will use a travel-planning scenario to illustrate the 
features of ServiceCom in the demo. The demo starts with 
a request from the user about the services he/she wants 
and  the  conditions,  such  as  the ticket reservation, hotel 
booking, the dates, and price ranges, the preferences of 
the services, etc. The user will be presented with a set of 
dialog menus to specify, to select, and to modify, and to 
invoke.  We  will  also  demonstrate  that  the  resulting 
composite web service can be published as a new service 
and  its  configuration  is  stored  and  can  be  re-used  and 
extended. In summary we will demonstrate the following 
features of the tool: supporting an integrated environment 
for  service  composition,  which  includes  composition 
specification,  planning,  implementation,  and  execution. 
Furthermore,  we  will  demonstrate  that  ServiceCom 
supports composition publishing, re-use, and extension in 
a light-weighted manner, which enables it to be executed 
in  different  enterprise  settings  without  too  much 
implementation overhead. 
 
4. Contributions 
 
In  this  paper  we  gave  a  short  description  of 
ServiceCom,  a  light-weighted  tool  for  service 
composition. This tool covers the complete life cycle of 
service composition, including the description, planning, 
building and executing of compositions. To the best of our 
knowledge there currently do not exist any other tools that 
provide  such  an  integrated  approach  to  service 
composition.  Most  importantly,  because  ServiceCom  is 
based  upon  the  service  component  mechanism,  it 
promotes reusability and specialization in the specification 
of  compositions.  This  sets  it  apart  from  other  service 
composition tools based upon more traditional languages, 
such  as  BPEL4WS.  Furthermore,  in  the  building  of 
service compositions reuse of class files is supported, thus 
shortening the building process increasing its efficiency. 
 References  
 
[1] F. Curbera, Y. Goland, J. Klein, F. Leymann, D. Roller, S. 
Thatte, S. Weerawarana; "Business Process Execution Language 
for Web Services", July 31, 2002, 
http://www-106.ibm.com/developerworks/webservices/ 
library/ws-bpel/ 
[2]  Business  Process  Modelling  Initiative;  "Business  Process 
Modeling Language", http://www.bpmi.org 
[3] Workflow Management Coalition; “XML Process Definition 
Language”, May 22, 2001,  
http://www.wfmc.org/standards/docs/ xpdl 010522..pdf 
[4] F. Leymann; "Web Service Flow Language", 2001,  
http://www.ibm.com/software/solutions/webservices/pdf/ 
WSFL.pdf 
[5] E. Christensen, F. Curbera, G. Meredith, S. Weerawarana; “ 
Web  Service  Description  Language”,  15  March  2001, 
http://www.w3.org/TR/wsdl 
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Challenges of Service Composition", ICDE-RIDE workshop on 
Engineering E-Commerce/E-Business, San Jose, USA, 2002 
[7]  J.  Yang,  M.P.  Papazoglou;  "Service  Components  for 
Managing the Life-Cycle of Service Compositions", Information 
System, June 2003 (forthcoming) 
[8]  C.  Bussler;  "Work  Class  Inheritance  and  Dynamic  Work 
Class  Binding",  Proceedings  of  the  Workshop  Software 
Architectures  for  Business  Process  Management  at  the  11th 
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(CAiSE*99), Heidelberg, Germany, 1999  
[9] G. Kappel, P. Lang, S. Rausch-Schott, W. Retschitzegger; 
"Work  Management  Based  on  Objects,  Rules,  and  Roles", 
Bulletin of the Technical Committee on Data Engineering, Vol. 
18, No. 1, March 1995  
[10] M.P. Papazoglou, A. Delis, A. Bouguettaya, M. Haghjoo; 
"Class  Library  Support  for  Work  Environments  and 
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June 1997 
 
Appendix A - ServiceCom screen shots 
 
 
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Business Process Execution Language for Web Services&quot;,

Business Process Modelling Initiative; &quot;Business Process Modeling Language&quot;,

Class Library Support for Work Environments and Applications&quot;,

Coalition; “XML Process Definition Language”,

Service Components for Managing the Life-Cycle of Service Compositions&quot;, Information System,

ServiceCom: A tool for service composition reuse and specialization.

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