ASP.NET PDF Viewer using C#, VB/NET

This is, in effect, a remote method invocation it s a way for the client to ask the server to run some code and optionally get a return value (WCF is more flexible than this in general, but in the context of a web application, your communication patterns are constrained because clients will typically be behind a firewall) That s likely to be a perfectly good pattern for operations such as looking up a stock price or retrieving a weather forecast However, if you are building a photograph browser application, this would not be a great way to retrieve pictures You could make it work, but it s easier to use the mechanisms already built into the web browser for downloading images you d almost certainly want to make the bitmaps available for download via HTTP rather than using WCF.

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HTML and Silverlight have UI elements that know how to render images downloaded with HTTP Browsers are usually able to start rendering images without having to wait for the download to finish, and that s difficult to achieve with a method invocation idiom And by using normal HTTP image download, you d also get to take advantage of standard HTTP caching in your web browser and any caching proxies you may be using Plain old HTTP works better here than trying to fetch a bitmap using something resembling a method call..

More generally, if the information your client code works with looks like a set of resources that might be identified with URIs (Uniform Resource Identifiers; for instance, http://oreilly.com/) and accessed via HTTP you might want to stick with ordinary HTTP rather than using WCF. Not only do you get the benefits of normal HTTP caching when reading data, but it may also simplify security you might be able to take whatever mechanism you use to log people into the website and secure access to web pages, and use it to secure the resources you fetch programmatically.

A service that presents a set of resources identified by URIs to be accessed via standard HTTP mechanisms is sometimes described as a RESTful service. REST, short for Representational State Transfer, is an architectural style for distributed systems. More specifically, it s the style used by the World Wide Web. The term comes from the PhD thesis of one of the authors of the HTTP specification (Roy Fielding). REST is a much misunderstood concept, and many people think that if they re doing HTTP they must be doing REST, but it s not quite that straightforward. It s closer to the truth to say that REST means using HTTP in the spirit in which HTTP was meant to be used. For more information on the thinking behind REST, we recommend the book RESTful Web Services by Sam Ruby and Leonard Richardson, (O Reilly).

Building and deploying on Unix systems is generally a harder task than on Windows because there are many flavors of Unix. For each of these flavors there can be several different desktop environments. (The desktop environment is what the user sees and uses, and can handle start menus, docks, window styles, and so on.) Handling all these combinations means that there are several ways to do things and many variations of the right thing to do. Another issue that needs to be addressed is that the Qt library might already be installed on the system that you are targeting. You need to find out what version and where, which you can do in at least two ways. One way is to link your applications statically to Qt, which means larger executables and no automatic updates if Trolltech decides to release an update of your Qt version. The other option is available only for Linux systems. You can require the system to support Linux Standard Base (LSB) because Qt 4.1 is available as an optional LSB module. Visit http://www.linuxstandardbase.org for more information. Now take a brief look at how your Qt application can be integrated into the current desktop environment after it has been installed properly.

Using WCF typically requires less effort than designing a RESTful service you can get up and running with a good deal less thought and forward planning (although you might not consider a lack of thought and planning to be a good thing for your particular application). But if the communication you require with your server doesn t sound like it fits well into a method-call-like style, you ll probably want to consider alternatives to WCF. Occasionally, neither WCF nor plain HTTP will be the best approach when connecting a web UI to a service. With Silverlight, you have the option to use TCP or UDP sockets from the web browser. (The UDP support is somewhat constrained. Silverlight 4, the current version at the time of writing this, only supports UDP for multicast client scenarios.) This is a lot more work, but it can support more flexible communication patterns you re not constrained to the request/response style offered by HTTP. Games and chat applications might need this flexibility, because it provides a way for the server to notify the client anytime something interesting happens. Sockets can also offer lower communication latency than HTTP, which can be important for games.

Fashionable though web applications are, they re not the only kind of distributed system. Traditional Windows applications built with WPF or Windows Forms are still widely used, as they can offer some considerable advantages over web applications for both users and developers. Obviously, they re an option only if all your end users are