aQDen Application Architecture
N-tier applications have become the norm for building enterprise software today. To most people, an N-tier application is anything that is divided into discrete logical parts. The most common choice is a three-part breakdown: presentation, business logic, and dataalthough other possibilities exist. N-tier applications first emerged as a way of solving some problems associated with traditional client/server applications. With the arrival of the Web, this architecture has come to dominate new development.
The Microsoft Windows DNA technology has been a very successful foundation for N-tier applications. The Microsoft .NET Framework also provides a solid platform for building N-tier applications. Yet, the changes .NET brings should cause architects to re-think the instructions they have learned about designing N-tier applications in the Windows DNA world. Even more important, the fundamental support for XML Web services built into the .NET Framework allows building new kinds of applications that go beyond the traditional N-tier approach. Understanding how best to architect applications for .NET requires two variables: first, knowing "what" changes in this new world, and second, "how" to exploit the changes.
Likewise, aQDen was designed using the Microsoft Windows DNA technology and N-tier methodologies. This application architecture gives you the greatest flexibility in the design of your technical infrastructure. In the next section we will be reviewing the technical implementation methodologies of aQDen. In keeping with the N-tier architecture approach, we will be concerned with the following application components:
- Presentation Layer (Client)
- Application Layer
- Communications Layer (Distributed Communications)
- DBMS / Data Storage Layer
The first layer is the Presentation layer. This defines the client interface to the application. In many cases this is the application itself. In other implementations, this could be a Terminal Server, Citrix or Browser client interface.
The second layer is the Application Layer. It is interacted with by the user and communicates to the Communications Layer. This is where the work is defined and completed. The communications between the Application and Com are via ADO transactions.
The third layer is the Communications Layer. This facilitates the interaction between multiple data sources via definable and configurable protocols. In a distributed communications environment, it also allows for the distribution of data and processing objects.
DBMS / Data Storage Layer
The fourth layer is the Data Base Management System (DBMS) and Data Storage Layer. This provides a platform to store, manage and manipulate the data. In all existing installation of aQDen this is facilitated by Microsoft Windows SQL Server. However, because the communications with the Communications Layer is via ODBC, this could theoretically be accomplished by any reliable DBMS.
Enhanced Routing System (EHRS)
Another important concept of the aQDen architecture is the Enhanced Routing System (ERS). More on this subject will be covered in the next section.
The technical architecture of the aQDen environment is extremely flexible. There are a number of ways this infrastructure can be implemented. In this section you will be shown several methods for implementing this technology and advantages and disadvantages will be discussed.