World Wide Web Distributed Authoring and Versioning (WEBDAV): An Introduction1 E. James Whitehead, Jr. Dept. of Information and Computer Science University of California, Irvine Irvine, CA 92697-3425 Email: [email protected] Phone: (714) 824-4121 Fax: (714) 824-1715 1.0 Introduction Today the typical use of the World Wide Web is to browse information in a largely read- only manner. However, this was not the original conception of the Web; as early as 1990, a prototype Web editor and browser was operational on the Next platform, demonstrating how Web content could be read and written. Unfortunately, most of the world never saw this editor/browser, instead developing their view of the Web from the widely distributed text-based line mode browser. When NCSA Mosaic was developed, it improved the line mode browser by adding a graphical user interface and inline images, but had no provision for editing. As Mosaic 2.4 reached critical mass in 1993-4, “publish/browse” became the dominant model for the Web. However, the original view of the Web as a readable and writable collaborative medium was not lost. In 1995 two browser/editor products were released: NaviPress by NaviSoft and FrontPage by Vermeer. These products began developing a market for authoring tools which allow a user to edit HyperText Markup Language (HTML) [Ragg97] pages remotely, taking advantage of the ability to work at a distance over the Internet. In early 1996, NaviSoft and Vermeer were purchased by America Online and Microsoft respec- tively, presaging major corporate interest in Web distributed authoring technology. In 1995-96, Netscape released Navigator Gold, a Web browser/editor tool, with the ability to publish pages to a remote Web server. 1996-7 also saw the release of Web-integrated word processors, with Microsoft Word 97, Lotus WordPro 97, and Corel WordPerfect 7 all having HTML editing and remote publishing capability. In this setting, an ad-hoc collection of people interested in remote authoring (now known as the WEBDAV group) met first at the WWW4 conference in December, 1995, and then next at America Online in June, 1996. Comprised of developers working on remote 1. This paper was published in ACM StandardView, March 1997, Copyright (C) ACM, 1997. WEBDAV: An Introduction 1 authoring tools, and people generally interested in extending the Web for authoring, this group identified key issues encountered in writing these authoring tools. The group also found that there was a pressing need to develop standard extensions to the HyperText Transfer Protocol (HTTP) [FGM+97] for the following capabilities: • Metadata. The ability to create, remove, and query information about Web pages, such as its author, creation date, etc. Also, the ability to link pages of any media type to related pages. • Name space management. The ability to copy and move Web pages, and to receive a listing of pages at a particular hierarchy level (like a directory listing in a file system). • Overwrite prevention. The ability to keep more than one person from working on a document at the same time. This prevents the “lost update problem” in which modifi- cations are lost as first one author, then another writes their changes without merging the other author’s changes. • Version management. The ability to store important revisions of a document for later retrieval. Version management can also support collaboration by allowing two or more authors to work on the same document in parallel tracks. From its inception, the WEBDAV group has been working steadily to produce an interop- erability specification which defines HTTP methods and their semantics for the above capabilities. Work in this direction has focused on three documents, a scenarios document [Lass96], which gives a series of short descriptions of how distributed authoring and ver- sioning functionality can be used, typically from an end-user perspective, a requirements document [SVWD97], which describes the high-level functional requirements for distrib- uted authoring and versioning, including rationale, and a protocol specification [GWF+97], which describes new HTTP methods, headers, request bodies, and response bodies, to implement the distributed authoring and versioning requirements. The WEB- DAV group is currently working with the Internet Engineering Task Force (IETF) to become a working group in the Application Area, and is working cooperatively with the World Wide Web Consortium, which is providing technical assistance and help contacting interested people within the Web community. In the remainder of this article, the rationale for developing a standard for Web distributed authoring and versioning is presented, followed by an detailed overview of the capabilities being proposed. Note that throughout this article the term “resource” is often used, which is the proper Web terminology for a any piece of information, such as a Web page, a docu- ment, a bitmap image, or a computational object which is stored on a Web server and whose location is described by a Uniform Resource Locator (URL) [BMM94]. 2.0 Rationale for a WEBDAV Standard While open standards are currently very popular, in part due to the success of the Internet, it is worthwhile to examine the reasons for developing an interoperability standard for Web distributed authoring and versioning. There are two primary arguments in favor of developing such a standard: WEBDAV: An Introduction 2 1. Emerging interoperability problem. There is currently an interoperability problem due to nonstandard HTTP extensions employed by commercial HTML editing tools. This problem will only get worse if an interoperability standard is not developed. 2. Collaboration infrastructure needed. Intranet enabled applications want to provide Web-based collaboration support, but currently have no standard way to provide it. 2.1 Emerging Interoperability Problem Today, the HTTP (version 1.1) protocol contains functionality which enables the editing of web content at a remote location, without direct access to the storage media via an operat- ing system. This capability is exploited by several existing HTML distributed authoring tools, and by a growing number of mainstream applications (e.g. word processors) which allow users to write (publish) their work to an HTTP server. To date, experience from the HTML authoring tools has shown they are unable to meet their user's needs using the facilities of the HTTP protocol. The consequence of this is either postponed introduction of distributed authoring capability, or the addition of nonstandard extensions to the HTTP protocol. These extensions, developed in isolation, are not interoperable. Distributed web content authoring tools that directly write content to an HTTP server cur- rently exist, exemplified by Microsoft FrontPage, America Online AOLpress, and Naviga- tor Gold and Communicator from Netscape. While these exciting tools demonstrate the enormous potential of a writable web, they also embody the interoperability pitfalls which lie ahead. While all three tools now can use the HTTP “PUT” operation to write their con- tent to a remote server, all three products use differing, custom HTTP extensions for non- standard capabilities. For example, both AOLpress and FrontPage use different HTTP extensions to retrieve information about which documents are located at a remote site, and both the FrontPage server extensions and AOLserver, the companion server to AOLpress, handle access control differently. One cannot currently use FrontPage with the AOLserver, or use AOLpress with the FrontPage server extensions. Furthermore, recent announce- ments by Novell and Lotus indicate they plan to offer Web servers with authoring support later this year, a foreshadowing of more serious interoperability problems still to come. 2.2 Collaboration Infrastructure Needed With the incredible growth of organization-specific webs, or intranets, a new class of tool is emerging: the Web-enabled tool. Just as distributed web content authoring tools cur- rently write to HTTP servers, a large class of more traditionally mainstream applications can now read and write information from HTTP servers. For example, Word 97 and Word- Pro 97 all now have the capability to import and save HTML documents via HTTP. Web- enabled spreadsheets are also now available: 1-2-3 97 and Excel 97 both have the ability to import data via HTTP, and to export spreadsheets in HTML via HTTP. Though limited to simple HTML import and export capabilities right now, these tools are poised to take advantage of the WEBDAV specification once complete, and provide network-based col- laborative editing features. The collaboration infrastructure provided by the WEBDAV specification provides the necessary foundation which these collaborative tools would use WEBDAV: An Introduction 3 to provide collaboration features to their users, and the lack of such a standard is prevent- ing the introduction of these tools today. 3.0 Functionality Overview The WEBDAV group has proposed a set of features which can be used in a wide variety of settings by applications which support collaborative work on remotely authored and ver- sioned documents. These features can be partitioned into four groups: metadata, name space management, overwrite protection, and versioning. A detailed overview of these capabilities along with a snapshot of current plans for how these features should be speci- fied are presented in the sections below. Many of the approaches described in this article are still being actively considered by the WEBDAV group, and hence this presentation should be considered a glimpse into work in progress, rather than a definitive statement about the final design. The WEBDAV functional requirements are presented in a compan- ion article, “Requirements for Distributed Authoring and Versioning on the World Wide Web,” also in this issue. 3.1 Metadata Support Information on the Web has many pieces of associated information, such as the title, sub- ject, creator, publisher, length, and creation date, of the information. This information about information (or metadata) can be used to search for Web resources, enforce copy- rights, or provide bibliographic information.