Chapter 14. Custom WebDAV Applications

When WebDAV is used for an application that includes but goes beyond simple distributed authoring, it is a custom WebDAV application. The application can be as simple as a few business rules acting on custom property values or as complex as Exchange 2000. This chapter discusses the advantages of using WebDAV for custom applications, the issues involved, and some examples.

Before the ubiquity of the Web, custom applications typically involved custom client code. That meant that client software had to be installed on users' computers. Users don't like installing software, but a client application is sometimes the only way (even today) to present a usable interface with required functionality. If the custom application ever requires added functionality after initial deployment, then the difficulty and cost of upgrading the deployed base of client applications is huge.

With the Web, many more custom applications can be designed to use server-side code alone. Many user interfaces can be done entirely in HTML, with HTML form submissions when the user needs to perform an action. Web-based custom applications are now very common, featuring many useful tools to cut down on development and deployment costs. However, many Web-based custom applications are also slow, suffering from poor user responsiveness, poor scalability, or both.

The development of client-side scripting helped Web applications designers cut costs and improve the usability of a custom Web-based application. Client-side scripting improves performance when it reduces the number of requests that need to be made. Although the client must download the script in addition to the Web page, if the script reduces roundtrips at all, performance is improved because that's where the real costs are incurred. If you've designed Web applications to use client-side scripting, then you're aware that scripting requires careful design, making decisions about what gets done where.

In many of the same ways, WebDAV can be another valuable tool to cut Web application costs. As a bonus, WebDAV is far more standardized than client-side scripting!

This chapter discusses first how to use WebDAV to augment an existing application without writing any client-side code (not even a browser-run script) and very little server-side code, in the context of an online photo album or other picture storage repository. Second, a more complex example shows how WebDAV was integrated into Exchange 2000. Among other things, this example shows how browser-executed script can use WebDAV to host an application that is faster than customer Web-hosted applications where the browser downloads server-generated pages without client script. Because so many client applications already support WebDAV, neither of these custom applications requires any software to be installed by the user.

The third example in the chapter is instant messaging. That example includes some suggestions where not to use WebDAV as well as some ideas how WebDAV can happily integrate with other protocols. Finally, a problem-solving environment for research organizations shows how much more flexible a WebDAV property schema is than traditional database-backed custom application schemas.