Explainer: WebDAV

As more and more enterprises use project teams with members based in different locations and time zones -- often in different countries or hemispheres -- their need for effective electronic collaboration tools has grown dramatically. There are a number of products that aim to solve that problem, and most make at least some use of a single underlying technology.

Web-based Distributed Authoring and Versioning (WebDAV or, more often, just plain DAV) is a standard that extends the capabilities of HTTP 1.1, the underpinning of the World Wide Web.

HTTP lets users read content that has already been published on the Web, but it provides no simple way for users to post new content or edit existing Web documents.

The protocol has no standard method for moving a file, locking or unlocking it, or adding property information to the file. WebDAV standardizes all of those functions, making the Web writable as well as readable in an interoperable way.

WebDAV was first proposed in 1996, and the current standard, RFC 2518, was published by the Internet Engineering Task Force (IETF) in February 1999. Versioning extensions to WebDAV were codified in RFC 3523 in March 2002.

Diving into DAV

WebDAV extends HTTP by adding new functions, including the following:

- Delete: for deleting a document or other resource.

- PropFind and PropPatch: for reading and writing metadata (also called properties) for a resource.

- MkCol: for creating a new DAV collection (think of folders for organizing files).

- Copy and Move: for copying or moving a resource.

- Lock and UnLock: for protecting editing changes when multiple users access the same document.

- CheckOut and CheckIn: for enabling version control and revision tracking.

HTTP headers aren't long enough to handle some requests, so WebDAV uses XML to format such requests and to store all resource properties. WebDAV version control also makes it possible for users to know which version of a file is the most current.

WebDAV at Work

Let's say you're collaborating on an engineering project with two or more groups in distant locations. You probably use e-mail to communicate with one another about the project's status, and you send document revisions back and forth, with everyone hanging onto copies.

If you're lucky, your organization has a document management or collaboration system to help keep things organized, as well as a version-control system to help track changes. But what if you don't have those resources?

With WebDAV-compliant software, team members can edit Web documents stored on a common Web server that's accessible on your network and over the Internet (safeguarded as needed by firewalls and virtual private networks) from any member's browser or other software.

A file-locking mechanism prevents one person from accidentally overwriting another's changes when they are working on the document at the same time. And you can limit access rights, store versions for later retrieval and maintain metadata such as authorship and modification dates.

Interoperability

WebDAV has been making strong inroads into Web infrastructure products.

The two leading Web servers -- Apache and Microsoft Internet Information Server -- are compliant, as are document and content management systems from Documentum, Vignette and BroadVision.

Other popular software tools that support DAV include Microsoft's Office XP, Office 2003 and SharePoint Portal Server, as well as Macromedia's Dreamweaver, and Adobe Systems' GoLive and Acrobat.

WebDAV functionality is embedded in operating systems including Windows (from Windows 95 onward), Apple Computer's Mac OS X and Novell's Netware. Windows XP's integrated support enables any application running on it to be WebDAV-enabled.

DAV's Future

In many organizations, static documents have evolved into active documents and interactive forms over corporate networks. With WebDAV support widely available, Web authoring is also likely to expand from local Web servers and intranets to encompass the entire Web, simply because new software will support seamless collaborative authoring.

The DAV Searching and Locating (DASL) group, which is related to the IETF, is working to develop a way to search a WebDAV-compliant repository on any platform. The DASL technology's main function will be the ability to search for Web resources based on their properties and text content. Another working group is addressing the issue of access control.

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