Edzus Zeiris and Maris Ziema
Faculty of Computer Science and Information Technology, Riga Technical University, Meza 1/3, LV-1048, Riga, Latvia
Keywords: SOA, e-Services, e-Business, Web services, QoS, Design methods, Multi-criteria optimisation, System
architecture, Algorithm graph.
Abstract: The development of e-business promotes the creation of new e-services; consequently, ways of fast and
quality designing of e-services are required. When developing e-services in SOA, it is very important to
build the architecture of e-business system that makes the e-service compliant with all and any quality
criteria (QoS) specified for it, which would expand its usability; furthermore, it is necessary to implement
any changes swiftly and in good quality to be able to adjust to the rapidly changing business environment.
This means that effective design methods should be used in creating e-business systems and e-services,
which would ensure the building of an acceptable e-business system architecture. A drawback of the
existing methods is the subjective opinion of the system’s architect, and that may not always lead to the best
solution. Therefore, it is possible to apply the Quality Attributes Driven Design method for web services
that is based on the use of formal optimisation methods. Initially the e-service is described as an algorithm
graph, and by segmenting its vertices in all possible ways the web service graphs are obtained. The
segmentation of the algorithm graph means that all the possible solutions that can affect the quality of the e-
service system architecture are dealt with. Using multi-criteria optimisation, a Pareto optimality set is
obtained from all the web service graphs. Web service graphs of the obtained Pareto optimality set can serve
as the basis for selecting an acceptable e-business system architecture.
The global dynamic advancement of information
technologies has reached a level where there is high
demand for simple and effective means for
receiving, processing, storing and exchanging
information. Information technologies have become
widely available to the public, and it creates demand
for e-services that facilitate the advancement of e-
business. There is a particular need for e-services in
the public sector (government and local government
spheres), where there is a very wide range of
customers and the number of services is high. More
and more government and local government
institutions offer their customers services that can be
delivered electronically. Compared to government
and local government institutions, the advancement
of e-services is faster in the private sector. The
reason for the advancement of the e-business
environment in the private sector could be cost-
effectiveness. In the long run, the use of e-services
saves resources, which means profit for private
commercial structures. Areas where commercial
e-services are most advanced are internet banking,
internet shops, information publishing,
communications etc. In the public sector, the
implementation of e-services is hindered by the
bureaucracy and the existing legislation procedures
that require a lot of work and time to make them
Undoubtedly, the availability, range and variety
of e-services are required for the convenience of the
customers (service users) and to save resources of
the service providers. If the range of e-services
becomes wider, the clients will benefit from saving
their time and resources; therefore, it is important to
expand the range of e-services both in the public and
private sectors. Development costs are one of the
factors that hinder the implementation of e-services.
Another factor, which, in terms of making services
electronic, affects more the public sector, is the
requirements to change the legislation and
procedures. Also, it is essential that simultaneous
processing of a number of communication channels
has to be considered when making services
electronic in the public sector. Since services of the
public sector must be available to all customers, it
Zeiris E. and Ziema M. (2010).
In Proceedings of the International Conference on e-Business, pages 265-272
DOI: 10.5220/0002921102650272
Figure 1: e-Business system architecture
has to be ensured that they can receive services on
the Internet, in presence, by phone, mail, e-mail etc.
In the development of e-services, another
problem is the rapidly changing business processes
that require relevant modifications of IT systems,
inter alia e-services. To develop e-service systems in
such a dynamic environment, a fast and quality
design method that makes it possible to adapt to the
business processes and satisfies all the requirements
specified for the e-service system is required. It is of
great importance to meet the quality of service
(QoS) requirements that is the basis for developing a
successful e-business.
Currently, the provision of services in the form
of web services is advancing at a rapid pace. This is
due to the fact that the business-related functionality
is offered as ready-made applications (services).
Usually a number of web services are combined in
e-services. To create an e-service, it is necessary to
strictly define service interfaces and their
functionality and to organise the performance of the
e-service in certain succession. It means that e-
business systems are created on the basis of SOA.
Several quality criteria can be specified for the e-
business system, and its architecture must comply
with them: development costs, maintenance costs,
integrity, scalability, security etc. To evaluate the
quality of system architecture, ISO 9126 Standard
for Software Engineering-Product Quality
Assessment and its quality metrics and guidelines
for the use thereof can be used.
Quality criteria are usually mutually
controversial; therefore, to be able to comply with
all the quality criteria set for the system, it is
necessary to design a system architecture that, to a
larger or lesser extent, meets all the requirements. In
such cases, it is not enough to use functionality-
based or object-oriented design approach. It is
necessary to apply methods that solve architecture
design quality problem.
To ensure the creation of an acceptable e-
business system architecture and to be able to adjust
e-services to the constantly changing business
environment and its requirements, it is possible to
employ formal optimisation methods in the
designing of the system architecture.
On the whole, an e-business architecture, within
which e-services are designed, is rather complex and
consists of a number of parts. It includes all the
components, conditions and mutual links required to
design e-services. Fig.1 shows how the systems and
system components used in the service are combined
into a single e-business system architecture.
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Fig. 1. shows how the systems and system
components used in the service are combined into
unified e–service system architecture. For every data
object that is required in the implementation of e–
service, an XML Schemas Catalog has to be
developed. Data call from the relevant functional
system is done by means of the web services. When
web service calls are done, also metadata that
describe the request are sent. Also any information
that is required for the audit trails is sent together
with the metadata. Web services can be distributed
into two groups: simple and complex. Complex web
services in fact are logical combinations of several
simple web services that result from the process
integration requirements; a combination may
comprise simple services of one or several
independent functional systems. Complex web
services can be executed by using a BPEL processor.
A BPEL processor is used as the orchestration
(integration) environment for the e–service’s web
services. Portals, one–stop agency applications etc
ensure the delivery of e–services to the users. E–
service entry forms, stop points, information on
payments and execution results are transferred
through HTML or HML pages that can be used in
the portal to implement the service using the XSLT
transformation. Web service and e–service holders,
i.e. institution specialists and system administrators
who are responsible for the maintenance and
development of web services and e–services, must
have a possibility to intercommunicate on various
issues connected with the execution and
advancement of web services and e–services. Also,
asynchronous e–services have to be executed.
Messaging systems are designated for this purpose.
The messaging system enables working with text
messages and work tasks. The application is inter-
integrated with the e–services register, from which it
receives data on XML schemas, web services and e–
services. On the other hand, the messaging
application is a client of the orchestrations as
messages on the execution of web services and e–
services are received from them. Data on all XML
schemas, web services and e–services are entered in
a single register called E–services Register. The
register keeps all the versions of schemas, services
and e–services so that this information is accessible
to anyone who is engaged in the development and
advancement of e–services.
The main problems in the e-business system
architecture are related to the e-service’s data
standardization, audit, the creation of a web service
catalog (UDDI), the execution of asynchronous e-
services, security and the development of e-service
orchestration that is connected with web service
design. If e-business environment components that
ensure quality e-services are once created, they can
be later used repeatedly, whereas web services of
particular e-services and their orchestration must be
developed for every e-service individually.
Furthermore, the development of web services and
their orchestration significantly affects the e-
service's performance metrics and, consequently, the
overall quality of e-service (QoS). To design web
services and their orchestration, the Quality
Attributes Driven Web Services Design Method,
which ensures swift and quality designing, can be
The offered e – business system architecture design
method consists of the following steps (Fig. 2.):
1. Initially it is necessary to create the e-service
algorithm graph G that describes the e-service to
be designed;
2. In the e-service algorithm graph, it is necessary
to determine the possible restrictions for inter-
segmentation of vertexes;
3. By recursively segmenting the e-service
algorithm graph, the web service graphs 
are obtained that are then used as the basis
for the development of the e-service system
architecture; The e-service algorithm graph is
assumed as the initial web service graph;
4. The numerical vales of quality metrics of the
obtained web service graphs are calculated;
5. From all the web service graphs, the Pareto
optimality set
is obtained;
6. Web service graphs of the obtained set P can
serve as the basis for selecting an acceptable e-
business system architecture. The web service
graphs that are contained in the obtained Pareto
optimality set can be designed in detail and
implemented in the e-business system
7. In most cases, the Pareto optimality set P
contains more than one solution. If the obtained
set is sufficiently small, the selection of web
service graphs from the set can be left to the
system designer. However, if there are many
possible solutions, then in order to select a
particular web service graph, the criteria can be
decreased or combined with another optimisation
or design method.
Figure 2: Quality attributes driven web services design method.
3.1 e-Service Algorithm Graph
The e-service algorithm graph is defined as an
oriented graph G
S, L
, where
is a final set – graph vertexes,
which, to their substance, are the executable
operations of the e-service algorithm, and LSS
are edges. The edge ls
in the graph means
that in the execution of the e-service algorithm the
execution of the operation s
is followed by the
execution of the operation s
. The edges in the e-
service algorithm graph show the information flow
(Fig. 3). When creating the e-service algorithm
graph that can be used as the basis for developing
the e-business system architecture, some of the
restrictions related to SOA have to be considered:
1. Every algorithm graph vertex s
must perform an
independent executable activity. It means that the
vertex operates in one transaction and is not
connected with the algorithms executed in other
vertexes. This condition is connected with high
cohesion and minimal dependence.
2. Every vertex must contain at least one executable
operation M
. In
practice, this is related to the algorithm
implementation methods.
3. 3. The operations that repeat during the
execution of the algorithm may not be
implemented in the graph as various vertexes
S, s
S, M
It is required in order to ensure high cohesion
and to exclude, from the very beginning, the
processing of unnecessary variants.
Figure 3: Example of e–service algorithm graph.
3.2 Web Services Graph
The basis for selecting the e-business system
architecture is the selection of web services. It
means that the e-service algorithm has to be
implemented as web services in order to design the
e-business system architecture. The algorithm graph
can be realised as a web service graph in several
ways: from realising every algorithm vertex as an
individual web service to realising all the algorithm
vertexes as one web service. It means that various e-
service algorithm graph segments can be realised as
web services, in this way changing the e-service
architecture and affecting various e-service
execution metrics (Fig. 4.).
Figure 4: Segmentation of the graph.
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To segment the graph and describe it formally, we
will deal with the graph G as the depiction
in the
vertexes set
, attributing to every vertex a sub-set
, which actually consists of the vertexes that
can be reached from the vertex
. 
is the edges
coming out from the vertex
, and
is the edges
going into
. For such e-service algorithm graphs,
there is at least one vertex
, which none of
the edges
, which we will call the origin
of the e-service algorithm, enters into; similarly,
there exists at least one vertex
, from
which none of the edges 
, which we will call
the result of the e-service algorithm, is going out. To
find all the possible web service graphs from which
the one to be implemented in the e-business system
architecture is selected, initially the given algorithm
is assumed as the first possible web service
graph. All other web service graphs are obtained by
segmenting the initial web service graph, which
concurs with the algorithm graph. Since several
segmentations are possible, the set 
contains all the possible graphs that are recursively
derived from the initial web service graph G is
defined. Graph transformations are done by merging
the vertexes. The combination
of the vertexes
is as the combination of the ingoing and
outgoing edges of both vertexes. 
. The set of methods in the
new created vertex develops as follows:
In practice, when creating the web service
algorithm graph, there are a number of restrictions,
e.g. it is necessary to integrate the functionality of
various systems in one e-service, or it is required to
use already existing web services. Therefore,
restrictions (vertex feature 
) can be applied to
the algorithm graph, which is assumed as the
original web service graph. In the given example
(Fig. 3.) vertexes 4 and 5 are created in another
system, therefore they are marked in another colour.
 In this case, the combination
of vertexes
only is possible if
Considering that the algorithm graph that initially is
assumed as the web service graph has attributed
features, the combination of vertexes
only is
possible if
Restrictions must be applied to the combining of
algorithm graph vertexes and the development of
web services also to be able to process large
algorithm graphs and find all the possible graph
vertexes segments. If there are no restrictions and
the algorithm graph is complex, segments have to be
extracted in the e-service graph, and then every
segment is treated as an individual design task. The
division of graphs is related to computation tasks,
where it is necessary to divide the graph in two (or
more) large parts, minimising the number of edges
that cross the split.
Obtaining all the possible algorithm graph
segments is an NP–complete problem, where all the
possible web service graphs only may be obtained
by executing a recursive algorithm.
3.3 Pareto Optimality Set
There are several criteria that have to be taken into
account when selecting an acceptable e-business
system architecture, and very often they are
contradictive. It means that it is necessary to find a
web service graph in the set X (which has been
formed after segmenting the algorithm graph) that is
the best (or at least not worse) according to the
specified quality criteria and on the basis of which
an acceptable e-business system architecture can be
build. It is very essential to deal with all the criteria
simultaneously, as it is impossible to determine
which of them is more important, and also, they are
not mutually comparable. The task of finding the
web service graph can be reduced to a multi-criteria
optimisation task. Multi-criteria optimisation means
finding the Pareto optimality in the sets, which can
be formally defined as follows:
are criteria to be
– X definition area. The solution
 will be called a Pareto optimality if and only
 does not exist such that
for all 
, where at least one is a strong
inequality. In other words, for any value
 in
the set
no better than the selected value can be
found according to every criterion to be optimised.
Depicting the Pareto optimality set graphically by
two criteria to be optimised, they are all solutions
that are nearest to the origin (Fig. 5.)
To be able to mutually compare and view
simultaneously various criteria to be minimised, they
must be normalised.
In the selection of the web service graph, the
application of the Pareto optimality set is done as
follows. An e-service algorithm graph is given.
Initially it is assumed as the web service graph G.
The task is to find the web service graph set
Figure 5: Pareto optimality set.
, which is defined in the area (i.e. all
possible algorithm graph segment combinations).
The criteria Q, which are the quality criteria
specified for the system, are minimised. To
determine the system quality criteria, it is possible to
use the following methods: scenario-based,
simulation-based, mathematical model-based and
The application of the Quality Attributes Driven
Web Services Design Method has been analysed by
using a number of study examples; also, e-business
system architecture designs obtained by using this
design method and classical object-oriented or
functionality-based design methods have been
compared. E-services developed for Latvian
government and local governments in the portals, and have been used to analyse and
approbate the method. The method analysis and the
offered e-business system architecture are based on
VISS, Latvian Government Information System
Integrator, which is an environment for e-services
and integration for government and local
government services. There are similar e-business
and integration systems also in other countries, for
example, X-road in Estonia, PSB in Ireland, OIO in
Denmark, GovTalk in the UK etc.
Analysing the results obtained from by using the
method and comparing them with already
implemented e-services, it can be seen that the
design method can be used in practice and that it
does not have any apparent drawbacks that exclude
any essential solutions. The used design methods are
different as to the resources that are required for
building an acceptable system architecture. It was
established that several e-services had been
developed iteratively during several years,
improving them constantly to achieve the desired
quality, and that several service versions that include
improvements in the system architecture had been
released. To develop an e-service, a number of
experienced system architects had been engaged,
which means that resources had been considerably
consumed. The offered method achieves the same
result by engaging one system architect only and in a
comparatively shorter period.
4.1 Design Methods Comparison
To design a complex e-business system, often it is
not enough to use one design method, instead,
several methods must be combined to meet the
required quality of service (QoS). There are several
methods that ensure that the required QoS level is
achieved, like Attribute Driven Design (ADD),
Software Architecture Analysis Method (SAAM),
Jan Bosch architecture design method, Architecture
Tradeoff Analysis Method (ATAM), Hazard
Analysis of Software Architectural Designs
(HASARD) etc.
Considering that in the result of using the
Quality Attributes Driven Web Services Design
Method a Pareto optimality set that contains several
results is obtained, then in more complex cases when
the system architect is unable to make a selection
from the Pareto optimality set, any other design,
decision-taking or optimisation method that helps
select a solution from the Pareto optimality set can
be applied. In this case, the possibility that a local
minimum is selected is excluded.
For the system architect to be able to select an
acceptable for them design method, a comparison of
methods by the following assessment criteria is
1. Multi-Criteria – in selecting the design method, it
is important to see to that all the quality criteria
specified for the system are dealt with
2. Is the subjective expert position excluded – in
many design methods, the selection of solution
depends on the system architect, whose
subjective opinion influences the system to be
3. Can be estimated in advance – since the
development of a system is very time-
consuming, it is essential that the quality
characteristics can be assessed prior to
commencing it;
Pareto solutions
Other solutions
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Table 1: Comparison of architecture design methods.
Comparison Nr.
1. 2. 3. 4. 5. 6.
Functional based No No No No Yes
Object-oriented No No No No Yes
ADD Yes No Yes No Yes
SAAM Yes No Yes No Yes
Jan Bosch Yes No Yes No Yes
Partly, there is more
than one expert.
Yes No Yes
Partly, method is oriented
to achieve security
No Yes No Yes
Quality Attributes Driven Web
Services Design Method
Yes Yes Yes Yes No Formulas
Combined Quality Attributes
Driven Web Services Design
Partly. To select
solution from Pareto
compromise set there
additional analysis is
Yes Yes Yes
4. Pareto Guaranteed – if the solution is selected
from among all the solutions in the Pareto
optimality set, it is sure that the selected
solution is one of the best possible;
5. Exact Solution – it is important to make sure
whether the design method provides one or more
6. Accuracy of the Solution: expert – the accuracy
of the solution is determined by the system
architecture’s experience; methodology – the
accuracy of the solution is determined by
complying with the descriptive methodology;
formula – the accuracy of the solution depends
on the accuracy of the formulae used. As it can
be seen from the given comparison (Table 1),
there are methods that are multi-criteria and that
make it possible to evaluate the quality
characteristics of the system architecture prior to
development; however, the accuracy of these
methods relies only and solely on the expert’s
experience and the compliance with the
methodology. It means that the possibility that a
local minimum is selected is not excluded.
Another drawback of these methods is the fact
that the subjective position of the expert is not
excluded, as in most cases only one system
architect that takes the decision is engaged in
system designing. Considering that successful
advancement of computer systems relies upon
their quality, any methods that are not multi-
criteria often do not provide the desired result.
The application of these methods can cause loss
both to the client who ordered the computer
system and the developer.
The existing multi-criteria design methods are
acceptable in designing large and complex computer
systems, which cannot be formally described and for
which the mathematic multi-criteria optimisation
methods cannot be applied. In such cases the ATAM
method, which involves several system design
experts, could be very efficient. Also other methods
looked at herein could be useful in designing large
computer systems if competent experts of the
relevant sector and who can take decisions and
evaluate the quality characteristics of the computer
system to be designed are called in.
To design the e-service system architecture, a
design method that provides fast and quality result
regardless of the qualification of the involved
experts is required. Since the e-service algorithm can
be described formally in the form of an algorithm
graph, it is possible to use the offered web service
design method and the selection of an acceptable e-
service system architecture that is based on multi-
criteria optimisation. In such and similar cases, it is
the multi-criteria optimisation method that should be
used to prevent that a local minimum is selected.
Considering that in the result of multi-criteria
optimisation a Pareto optimality set that contains
several results is obtained, then in more complex
cases, when the system architect is unable to make a
selection from the Pareto optimality set, any other
design, decision-taking or optimisation method that
helps select a solution that is contained in the Pareto
optimality set can be applied. In this case, the
possibility that a local minimum is selected is
To meet all the quality requirements set for the e-
service, it is important to select an e-business
architecture design method that is multi-criteria, as
the quality criteria are mutually controversial;
otherwise there is a possibility that, while improving
one of the quality criteria, another potentially
significant condition is not dealt with. If a multi-
criteria design method is selected, a compromise
among the quality criteria of the e-service is found.
A drawback of other design methods is the
subjective position of the designer that affects the
quality metrics of the designed system and might
lead to selecting a local minimum, thus leaving out
the best possible solution.
The Quality Attributes Driven Web Services
Design Method ensures swift and quality designing
of web services, which is the basis for the e-business
system architecture and affects the QoS of the e-
service. By applying this method, it is possible to
optimise the system design costs.
The offered Quality Attributes Driven Web
Services Design Method can be used also in other
systems that are not complex algorithmically (i.e.
algorithm graph can be built) and are based on SOA
and web services.
This work has been supported by the European
Social Fund within the project „Support for the
implementation of doctoral studies at Riga Technical
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