So What's a Client/Server Application?

Standard Visual FoxPro applications

Most Visual FoxPro applications are what we call file/server applications. Essentially, the information is stored in a collection of standard Visual FoxPro DBF files. Those files exist either on one computer that acts as both the workstation and the server, or on a server computer that is accessed by more than one other computer. All the server does in this configuration is allow other users and workstations to access the information. It doesn't do any special processing.

Client/Server applications

In a client/server environment, the biggest difference is that the server does extra work. Database servers like Microsoft's SQL Server handle a large portion of the processing work so that the workstations don't have to. This allows other advantages, like additional security. The security features that are a part of SQL Server run only on the server, so users and workstations can't get to the information on the server unless the database server is set up to allow it.

When do I need client/server?

You can probably guess the answer to this question already. You need client/server when you need the additional features that it gives you. If you need larger files than you can create with the standard DBF format, or if you need extra security for your application, you need the client/server features. Generally, the guidelines are:

• More than 2 GB of information in any one table
• More than 50 users
• More than several million records
• Tight security is a requirement

If you don't have at least one of these requirements, you can safely use DBF files and avoid the licensing costs for a database server. If you believe you'll someday need them, we can use a limited license version of SQL Server so you can easily upsize later on.

We are happy to use either file/server or client/server techniques for your application.

What is a tier, and what does n-tier mean?

When you decide to go with a client/server solution, you automatically wind up with a minimum of two sections in your software. One section is the database server, which runs either on a server by itself or on your network server. That is by default, your data tier. Because your database server lives on your server and doesn't have any workstation access, you need a minimum of one other program for your client workstation. The program your users see is referred to as the UI tier.

Generally speaking, when you go all the way to client/server, you won't want to stop at just a program on the workstation plus a database server. You'll usually also want to have a third layer in between to put all of the rules your business uses to handle its information. That's often called a business rules layer, or in this context, a middle tier.

UI tier

Your UI tier can use any of a wide variety of tools to present information to your users in a form that they can read and use it. You might use a Visual FoxPro program for this program, or you could use a web browser. Another possibility is a Visual Basic or C# program. McStyles Software specializes in Visual FoxPro or web browser front ends using Web Connection. If you have a preference for another approach, we'll team up with another custom software developer to provide the UI layer for your application. All the doors are wide open, and we'll do it the way you prefer.

Middle tier

Generally speaking, the middle tier is where Visual FoxPro truly shines in every application. Because Visual FoxPro is built around its own internal data processing language, it can usually run rings around most other tools when it comes to

• taking data from the database server
• applying your business rules to the data
• returning the data in a form that's usable by the UI layer

Data tier

This tier is your database server.

If your database server needs are modest, we'll handle setting up your database server and stored procedures. If your needs are greater and you don't already have a database administrator (DBA) on staff, you will probably require the assistance of a database server expert. In that event, we'll team up with an expert to provide the best possible service to you.

Ordinarily, you'll already have a database server in place of your choice, and most likely you'll also have someone that manages it for you. We'll work with that person to ensure that your custom Visual FoxPro application doesn't provide unnecessary stress on your database server. In that way, we can ensure your database operates smoothly.

This page was last modified on Tuesday, 07 November 2006