Case Study
3-Tier Architecture
This client manages a large number of mailing lists for their catalogs, and maintains order taking, fulfillment, and customer service departments which accept and process telephone orders generated by their
catalog mailings.
Although it’s current Visual FoxPro database has been successfully handling the large amount of data generated, it’s management wanted to be in the position to move the data over to SQL Server.
Among the requirements to be met were these:
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Allow the data to be accessed by feature-rich applications in the client's offices as well as allowing some of this data to be accessed via a browser across the internet.
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Leverage in-house programming expertise, code libraries, and programming standards.
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Allow the developed applications to work against the existing Visual FoxPro database before being “switched” to work against a corresponding SQL Server database.
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Have maximum flexibility so that new business rules and interfaces could be easily implemented without requiring major rewrites.
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Allow front-end development that could be contracted out, while the in-house IT staff concentrated on the implementation of business rules and on the storage of the data.
This client asked Waldner Associates, with whom it had already completed previous successful projects, to help it design and prototype an architecture that would allow it to make this transition smoothly.
Working with their IT staff, we designed and successfully prototyped a three tier solution which separated out:
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A Presentation Layer
These are applications that run on the user's desktop or in a browser. They adhere closely to the client's current application development standards, use much of the existing code base and business objects, and require only moderate changes to existing Visual FoxPro applications.
The user interfaces talks to a "facade" layer that can be switched to call upon middle layer objects specialized for processing Visual FoxPro data or those specialized for processing SQL Server data.
This presentation layer consists of:
Modified existing Visual FoxPro applications
New Visual FoxPro applications
Browser based applications, for accessing data via the Internet.
- A Business Layer
These are a collection of objects, developed in Visual FoxPro, which have as their major tasks:
Accept data handling requests from the presentation layer.
Enforce business rules and run business processes.
Talk to either the Visual FoxPro database or the SQL Server database.The objects talking to the database can be easily interchanged, thus allowing the application to work against either database.
These objects run under Microsoft Transaction Server to provide scalability.
ADO and XML are used to pass data between the layers.
- A Data Layer
The data itself resides in either a Visual FoxPro database or in a SQL Server Database.
In order to provide rapid data processing when dealing with SQL Server data, a number of stored procedures were developed to handle data intensive processes.
One of the major advantages of this architecture is that it allows much of the business code to be developed and tested while the data still resides in a FoxPro database.