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In the past decade, the software industry has evolved significantly, especially in the enterprise application development area. And the biggest evolution has been the transition from client/server applications to Web based applications.

Ten years ago, PCs were just starting to connect with networks, operating systems were starting to provide better graphical user interfaces, and the business database was beginning to dominate the enterprise application market. Back then, the business application developer created client/server applications. That type of application usually stored data in a central database server, with graphical user interface applications running on the client PC. The client application collected inputs from the end user and accessed the data from a central server. Since it made use of the rich user interface of the operating system and ran on the client machine, it came to be called a "rich client" application.

"Rich client" applications have several advantages. For example, they can leverage both the graphics user interface support from the operating system and the easy sharing of information provided by the network. Usability improved a lot compared to the previous applications that ran on standalone machines.

As time went on, the shortcomings of rich client applications were gradually identified. The most important drawback was the difficulty of application deployment, especially when you have to install or update the application in a large enterprise. The iterative installation/update process is a painful experience and it is definitely time-consuming. (Table 1)

The Internet boom changed the world and changed the enterprise application model. Internet applications are also called Web-based applications. Web application logic is different that rich client applications because in a Web application the the business logic runs on the server and only a simplified user interface shows on the client browser. Since there's no rich user interface and no relatively complex UI programming work, the client portion of the application is "thin" compared to the "rich client" application, so we call them "Thin Client" applications.

Web-based applications resolve the deployment problems of rich client applications. Once a change is published to the Web server, all the users get the change immediately. This saves spending a lot of money and effort on the enterprise application maintenance lifecycle.

Web applications started to dominate the market as the Internet wave grew. But it wasn't a perfect solution. While we solved the deployment headache with Web applications, the tradeoff was that we lost some special power of the rich client application. For example, the responsive user interface like "drag & drop" was lost and resources on the local client computer couldn't be fully utilized. Furthermore, if the network connection was down temporarily we couldn't do anything with the application. End users started to find thin client applications were often less productive than rich client applications.

There is a very interesting article from Jupiter Research (http://download.microsoft.com/download/9/5/e/ 95eafbc3-4d5d-4648-8aa6-589391068fb5/JupiterSmartClient.pdf) that indicates that "over a third of enterprises that already have Web-based applications installed want to switch their applications back to traditional rich client applications".

Is there a solution that can combine the power of rich client applications and the deployment ease of thin client applications? Yes, the answer is "Smart Client" application.

Introduction to Smart Client Applications
Smart client applications are designed to combine the traditional benefits of a rich client application with the deployment benefits of a thin client application.

Smart client applications have the following key characteristics:

• Allows for intelligent installation and update
• Supports occasionally connected operation
• Can make use of local resources
• Has a rich user interface
• Makes use of network resources

From this definition, we know that smart client applications are actually an extension of traditional rich client applications. So a smart client application offers almost all the advantage of a rich client application (e.g., the highly responsive user interface). And to address the pain of application deployment, smart client applications utilize functionality similar to Web applications. Furthermore, To reduce the network dependency of both rich and thin clients, an off-line application processing model was introduced for smart client applications.

In this article, I'll focus on the following three key aspects of creating a smart client application using PowerBuilder:

• Creating a PowerBuilder .NET Windows Form application
• Resolve the rich client deployment problem using Intelligent Updater
• Creating an "occasionally connected" applications with Mobilink Synchronization Objects

Overview of PowerBuilder Smart Client Application Development
Figure 1 shows the overall layered architecture of a PowerBuilder smart client application. It also shows the dependency relationship between each component. We can see that a typical PowerBuilder .NET smart client application consists of three major components: the PB.NET WinForm Application, Intelligent updater and Mobilink synchronization support. The PowerBuilder .NET smart client application is actually a WinForm application with easy deployment (using Intelligent Updater) and off-line support (using Mobilink).

The Intelligent Updater component is available only in a PB .NET WinForm application. But you can use Mobilink support in either a WinForm application or a traditional PowerBuilder Win32 application. So if you want to have all the powerful features of a smart client application, you have to build a WinForm application first.

In the discussion below, I'll go through the process of creating a real-world smart client application.

Building Windows Form Application in PowerBuilder 11.0
The architectural goal of PowerBuilder 11.0 is to support deployment to the .NET platform, which means making PowerScript applications run as a Windows Form or an ASP.NET Web Form application. Although it sounds ambitious, the implementation is actually fairly straightforward.

The .NET Windows Form application will be the next generation of PowerBuilder client/server-based applications. Over 95% of existing PowerBuilder native features are supported in the Windows Forms world. More importantly, with PowerBuilder .NET WinForm support you can leverage.NET features through PowerBuilder's .NET language interop. For example, you'll be able to use the features directly in .NET such as controls with a modern user interface, threading classes, algorithm libraries, and so on. Combine these .NET features with PowerBuilder special features like DataWindow, EditMask...And if it's easy for you to imagine how powerful it would be, a new door has just opened for you into the .NET world!

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