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http://www.spinellis.gr/pubs/conf/2004-PAKMOEM-MDA/html/KATSC04.htm This is an HTML rendering of a working paper draft that led to a publication. The publication should always be cited in preference to this draft using the following reference:
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Vassilios Karakoidas1, Stephanos
Androutsellis-Theotokis1, Diomidis Spinellis1, Yannis
Charalabidis2
1 Athens University of Economics and Business, 76 Patission Str., Athens,
10434, Greece, {stheotok, bkarak,
dds}@aueb.gr
2 Singular Software SA, 23rd km Athens-Lamia Road, Ag. Stefanos, 14565, Greece, yannisx@singular.gr
Abstract: This paper elaborates on the application of the MDA approach for achieve
interoperability among existing Enterprise Applications, such as Enterprise
Resource Planning (ERP) and Customer Relationship Management (CRM) systems,
through utilizing XML/B2B interconnection standards, developing components and
modifying existing systems where necessary. We present the PRAXIS project
design as a specific case study of this approach, describing the way in which
interoperability-oriented high level model mappings are providing the means for
guiding the model-driven development of interoperable Enterprise Applications.
Specifically, we focus on the transformation processes that drive the
Computation Independent System model into the Platform independent and finally
the Platform Specific Model, including our final design decisions for the
PRAXIS system.
Since the 1960s, Enterprise
Applications development suffered from a lack of available technological
solutions for organizing business processes [19]. To deal with this issue,
software engineers worked in the direction of developing software in the areas
of Relational Database Management Systems (RDBMS) and Rapid Applications
Development IDE (RAD). Researchers also developed methodologies for formalizing
the design of Information Systems such as the Soft Systems Methodology (SSM)
[21] [22] [23] etc. Recently, IEEE provided a series of guidelines for
efficient system design and development [20].
During the last two
decades, many sophisticated systems were also developed to provide common
ground for enterprise application development. These Enterprise Resource
Planning systems (ERP) are widely used nowadays in the design of modern Information
Systems (IS).
In the last few years,
however, the focus has shifted from the development of software systems to the
integration between them, in other words dealing with the problem of
interoperability.
Interoperability is defined
as [1]:
“… the ability of two or more systems or components to
exchange information and to use the information that has been exchanged”.
This is a particularly complicated task. Most systems
developed and in use today by organizations were deliberately alienated with
each other, making it very complex to find common ways to share business related
information.
While working on the
PRAXIS system [2], we made some interesting observations regarding the problem
of interoperability between enterprise applications.
Figure
1 shows an attempt to categorise the driving forces
that affect interoperability in Enterprise Applications development.
Figure 1 – Driving Forces of
Interoperability in Enterprise Applications
Technical Standards: Enterprise Applications are
based upon modern or legacy technical standards, such as XML [8], CORBA, and
Java. In trying to make a system interoperable, one has to consider a wide set
of standards in order to implement the solution.
Technology Trends: Technology trends pose serious restrictions
to interoperability. In fact, it is common practice that the implementation of an
interoperable system is attempted with the use of the most popular technology
instead of the most effective one. For example, the way in which XML [8] and
Web Services [13] affected Business 2 Business standards such as ebXML [9] and
UN/CEFACT [10]. Similarly, according to recent research papers, ontologies are expected
to be used as key technology for Enterprise Modeling [18].
Business Standards: These are often used as the
common language between enterprise systems. Attempts to design an interoperable
system often depend on the usage of one or more business standard, for example,
EDI [11], ebXML [9], RosettaNet [12]
etc.
Business Processes: It is a common case for
enterprises to achieve a level of interoperability in the business process
level. In fact, in order to design such a bridge, one must reengineer a set of
common business processes between the enterprises. In order to face
interoperability issues, an enterprise must perform some “light” Business
Process Rengineering (BPR). EbXML [9] is a widely accepted standard that is
trying to solve this problem.
Considering the
aforementioned facts, we attempted to find a formal and concrete way to design the
PRAXIS system.
The main
objective of the PRAXIS system [2], which is particularly targeted towards
SMEs, is to allow
the interconnection of existing
Enterprise Applications, such as Enterprise Resource Planning and Customer
Relationship Management (CRM) systems, as well as their seamless
interconnection with corresponding software applications of the public sector
and financial institutions. This is achieved through the utilization of XML/B2B
interconnection standards to support interoperability, the development
components and the modification of existing systems where necessary.
The goal is to
support a variety of transactions, ranging from invoicing and sales cycle
support to bank and tax payments.
It is expected that the SMEs which will adopt the
PRAXIS system will experience a significant reduction in the required time and
the rate of errors involved in carrying out the various transactions, which in
turn will offer an overall competitive advantage.
The Model Driven
Architecture (MDA) concept aims to facilitate the design and development of
wide-scale enterprise applications in an evolvable and flexible way, with
particular emphasis on interoperability [3].
MDA defines an approach that separates the system
functionality specification from its implementation on a specific technology
platform. In this way, the system architecture can be language, vendor and
middleware neutral.
Through the MDA approach, systems are modeled at the
following three different levels of abstraction and platform/technology
dependency:
Since the PIM, by definition, does not contain
technical details, it is envisaged that the PIM will be mapped to one or more
platform-specific models (PSM). The PSM is a refinement of the PIM to target
platforms such as Microsoft .NET (COM+), Enterprise JavaBeans (EJB) or the
CORBA Component Model (CCM). The PSM represents the source code or its UML
representation. There can be as many PSM as there are different implementations
of a given PIM.
Our system was designed using three levels of
abstraction as defined in the MDA methodology.
At the most abstract, Computation Independent System
(CIS) Model level, the proposed system would be described as shown in Figure 2.
Figure 2 - The Computation Independent System Model for the PRAXIS system
This abstract model illustrates the interoperability
requirements for different software applications owned by the same or different
enterprises that are expected to interact with each other. The various transactions
schematically illustrated in Figure 2, entail a variety of interactions between the
applications and lay out a set of complex functional and non-functional
requirements for the system to be designed and implemented, which must be
examined at the lower modeling levels.
It should be noted that the CIM model is abstract
enough to encompass any system architecture, including both client-server and
distributed approaches. The use of MDA describes and represents interactions
between entities, and not the way in which they will be implemented. The choice
of architecture and components that will be utilized is up to the next model
level.
In refining the CIM model to produce the Platform
Independent Model (PIM), the top-level system architecture needs to be designed.
In the PRAXIS system design phase it was decided [2] to adopt a client-server
architecture, consisting of a central server performing communication,
mediation and store-and-forward activities, and a set of client applications
that will run on the connected enterprise sites.
The server, which does not appear in the CIS model,
needs to be part of the PIM model, in order to produce a valid system
description that will be further refined at the platform-specific level.
Figure 3 illustrates the PIM level model for (a subset
of) the PRAXIS system (simplified for clarity). The model is divided in two
main modules, the server and client.
Figure 3 - Platform Independent Model for the PRAXIS system
The PIM design is based on UML notation [15] and
provides the bridge between the abstraction and the realization.
The transition from the PIM to the PSM model consists
of defining specific technologies and infrastructures for the various
components of the system. These mappings fill the gap between the abstract
model and the Platform Specific Model. The realization of our system is
depicted in Figure 4.
Figure 4 – PRAXIS System Architecture
In the case of the PRAXIS project, the central choices
were the following:
§ The server was implemented on
the .NET platform, using a mixture of C++ and C# code.
§ Data is stored in an MS SQL
Server Relational Database.
§ The following three types of
clients were implemented:
These three types of clients were provided in order to
reach out for SMEs that do not have the capability to support expensive ERP
systems.
A more detailed architecture schema is provided in
Figure 5.
Figure 5 – PRAXIS system architecture in detail
The communication is layered as illustrated in Figure
5. The base protocol is based on SOAP. Other protocols that might be needed to
achieve interoperability between distinct systems are supported through
layering them on top of SOAP, making the necessary transformations where
appropriate.
Figure 6 – PRAXIS Protocol Layers
This paper has presented the application of the MDA
approach in the design of a client-server application to support interoperability
among enterprises. It has illustrated the refinement steps that lead from the
more abstract to the technology-specific models, pointing out the specific
patterns of the design. We are convinced that these patterns can be extracted
and later used as common practice in similar situations. A direct extension of
our work may include the employment of Ontology-based approaches to be defined
in order to provide common knowledge [14] [16] [17] [18].
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