Requirements for a Distributed Authoring and Versioning Protocol for the World Wide Web
RFC 2291

Network Working Group                                          J. Slein
Request for Comments: 2291                            Xerox Corporation
Category: Informational                                       F. Vitali
                                                  University of Bologna
                                                           E. Whitehead
                                                            U.C. Irvine
                                                              D. Durand
                                                      Boston University
                                                          February 1998

        Requirements for a Distributed Authoring and Versioning
                    Protocol for the World Wide Web

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   Current World Wide Web (WWW or Web) standards provide simple support
   for applications which allow remote editing of typed data. In
   practice, the existing capabilities of the WWW have proven inadequate
   to support efficient, scalable remote editing free of overwriting
   conflicts. This document presents a list of features in the form of
   requirements for a Web Distributed Authoring and Versioning protocol
   which, if implemented, would improve the efficiency of common remote
   editing operations, provide a locking mechanism to prevent overwrite
   conflicts, improve link management support between non-HTML data
   types, provide a simple attribute-value metadata facility, provide
   for the creation and reading of container data types, and integrate
   versioning into the WWW.

1. Introduction

   This document describes functionality which, if incorporated in an
   extension to the existing HTTP proposed standard [HTTP], would allow
   tools for remote loading, editing and saving (publishing) of various
   media types on the WWW to interoperate with any compliant Web server.
   As much as possible, this functionality is described without
   suggesting a proposed implementation, since there are many ways to
   perform the functionality within the WWW framework. It is also

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   possible that a single mechanism could simultaneously satisfy several
   requirements.

   This document reflects the consensus of the WWW Distributed Authoring
   and Versioning working group (WebDAV) as to the functionality that
   should be standardized to support distributed authoring and
   versioning on the Web.  As with any set of requirements, practical
   considerations may make it impossible to satisfy them all.  It is the
   intention of the WebDAV working group to come as close as possible to
   satisfying them in the specifications that make up the WebDAV
   protocol.

2. Rationale

   Current Web standards contain functionality which enables the editing
   of Web content at a remote location, without direct access to the
   storage media via an operating 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 users' needs using the facilities of Web
   standards. The consequence of this is either postponed introduction
   of distributed authoring capability, or the addition of nonstandard
   extensions to the HTTP protocol or other Web standards.  These
   extensions, developed in isolation, are not interoperable.

   Other authoring applications have wanted to access document
   repositories or version control systems through Web gateways, and
   have been similarly frustrated.  Where this access is available at
   all, it is through nonstandard extensions to HTTP or other standards
   that force clients to use a different interface for each vendor's
   service.

   This document describes requirements for a set of standard extensions
   to HTTP that would allow distributed Web authoring tools to provide
   the functionality their users need by means of the same standard
   syntax across all compliant servers. The broad categories of
   functionality that need to be standardized are:

        Properties
        Links
        Locking
        Reservations
        Retrieval of Unprocessed Source
        Partial Write
        Name Space Manipulation
        Collections

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        Versioning
        Variants
        Security
        Internationalization

3. Terminology

   Where there is overlap, usage is intended to be consistent with that
   in the HTTP 1.1 specification [HTTP].

   Client
        A program which issues HTTP requests and accepts responses.

   Collection
        A collection is a resource that contains other resources, either
        directly or by reference.

   Distributed Authoring Tool
        A program which can retrieve a source entity via HTTP, allow
        editing of this entity, and then save/publish this entity to a
        server using HTTP.

   Entity
        The information transferred in a request or response.

   Hierarchical Collection
        A hierarchical organization of resources.  A hierarchical
        collection is a resource that contains other resources,
        including collections, either directly or by reference.

   Link
        A typed connection between two or more resources.

   Lock
        A mechanism for preventing anyone other than the owner of the
        lock from accessing a resource.

   Member of Version Graph
        A resource that is a node in a version graph, and so is derived
        from the resources that precede it in the graph, and is the
        basis of those that succeed it.

   Property
        Named descriptive information about a resource.

   Reservation
        A declaration that one intends to edit a resource.

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   Resource
        A network data object or service that can be identified by a
        URI.

   Server
        A program which receives and responds to HTTP requests.

   User Agent
        The client that initiates a request.

   Variant
        A representation of a resource.  A resource may have one or more
        representations associated with it at any given time.

   Version Graph
        A directed acyclic graph with resources as its nodes, where each
        node is derived from its predecessor(s).

   Write Lock
        A lock that prevents anyone except its owner from modifying the
        resource it applies to.

4. General Principles

   This section describes a set of general principles that the WebDAV
   extensions should follow.  These principles cut across categories of
   functionality.

4.1. User Agent Interoperability

   All WebDAV clients should be able to work with any WebDAV-compliant
   HTTP server. It is acceptable for some client/server combinations to
   provide special features that are not universally available, but the
   protocol should be sufficient that a basic level of functionality
   will be universal.

4.2. Client Simplicity

   The WebDAV extensions should be designed to allow client
   implementations to be simple.

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4.3. Legacy Client Support

   It should be possible to implement a WebDAV-compliant server in such
   a way that it can interoperate with non-WebDAV clients.  Such a
   server would be able to understand any valid HTTP 1.1 request from an
   ordinary Web client without WebDAV extensions, and to provide a valid
   HTTP 1.1 response that does not require the client to understand the
   extensions.

4.4. Data Format Compatibility

   WebDAV-compliant servers should be able to work with existing
   resources and URIs [URL]. Special additional information should not
   become a mandatory part of document formats.

4.5. Replicated, Distributed Systems

   Distribution and replication are at the heart of the Internet.  All
   WebDAV extensions should be designed to allow for distribution and
   replication.  Version trees should be able to be split across
   multiple servers.  Collections may have members on different servers.
   Any resource may be cached or replicated for mobile computing or
   other reasons.  Consequently, the WebDAV extensions must be able to
   operate in a distributed, replicated environment.

4.6 Parsimony in Client-Server Interactions

   The WebDAV extensions should keep to a minimum the number of
   interactions between the client and the server needed to perform
   common functions. For example, publishing a document to the Web will
   often mean publishing content together with related properties.  A
   client may often need to find out what version graph a particular
   resource belongs to, or to find out which resource in a version graph
   is the published one.  The extensions should make it possible to do
   these things efficiently.

4.7. Changes to HTTP

   WebDAV adds a number of new types of objects to the Web: properties,
   collections, version graphs, etc.  Existing HTTP methods such as
   DELETE and PUT will have to operate in well-defined ways in this
   expanded environment. WebDAV should explicitly address not only new
   methods, headers, and MIME types, but also any required changes to
   the existing HTTP methods and headers.

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4.8. Alternate Transport Mechanisms

   It may be desirable to transport WebDAV requests and responses by
   other mechanisms, particularly EMail, in addition to HTTP.  The
   WebDAV protocol specification should not preclude a future body from
   developing an interoperability specification for disconnected
   operation via EMail.

5. Requirements

   In the requirement descriptions below, the requirement will be
   stated, followed by its rationale.

5.1. Properties

5.1.1. Functional Requirements

   It must be possible to create, modify, read and delete arbitrary
   properties on resources of any media type.

5.1.2. Rationale

   Properties describe resources of any media type.  They may include
   bibliographic information such as author, title, publisher, and
   subject, constraints on usage, PICS ratings, etc. These properties
   have many uses, such as supporting searches on property values,
   enforcing copyrights, and the creation of catalog entries as
   placeholders for objects which are not available in electronic form,
   or which will be available later.

5.2. Links

5.2.1. Functional Requirements

   It must be possible to create, modify, read and delete typed links
   between resources of any media type.

5.2.2. Rationale

   One type of link between resources is the hypertext link, which is
   browsable using a hypertext style point-and-click user interface.
   Links, whether they are browsable hypertext links, or simply a means
   of capturing a relationship between resources, have many purposes.
   Links can support pushbutton printing of a multi-resource document in
   a prescribed order, jumping to the access control page for a
   resource, and quick browsing of related information, such as a table

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   of contents, an index, a glossary, a bibliographic record, help
   pages, etc. While link support is provided by the HTML "LINK"
   element, this is limited only to HTML resources [HTML]. Similar
   support is needed for bitmap image types, and other non-HTML media
   types.

5.3. Locking

5.3.1. General Principles

   5.3.1.1. Independence of locks. It must be possible to lock a
   resource without performing an additional retrieval of the resource,
   and without committing to editing the resource.

   5.3.1.2. Multi-Resource Locking. It must be possible to take out a
   lock on multiple resources residing on the same server in a single
   action, and this locking operation must be atomic across these
   resources.

5.3.2. Functional Requirements

   5.3.2.1. Write Locks. It must be possible to restrict modification of
   a resource to a specific person.

   5.3.2.2. Lock Query. It must be possible to find out whether a given
   resource has any active locks, and if so, who holds those locks.

   5.3.2.3. Unlock. It must be possible to remove a lock.

5.3.3. Rationale

   At present, the Web provides limited support for preventing two or
   more people from overwriting each other's modifications when they
   save to a given URI. Furthermore, there is no way to discover whether
   someone else is currently making modifications to a resource. This is
   known as the "lost update problem," or the "overwrite problem." Since
   there can be significant cost associated with discovering and
   repairing lost modifications, preventing this problem is crucial for
   supporting distributed authoring. A write lock ensures that only one
   person may modify a resource, preventing overwrites. Furthermore,
   locking support is a key component of many versioning schemes, a
   desirable capability for distributed authoring.

   An author may wish to lock an entire web of resources even though he
   is editing just a single resource, to keep the other resources from
   changing. In this way, an author can ensure that if a local hypertext
   web is consistent in his distributed authoring tool, it will then be

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   consistent when he writes it to the server. Because of this, it
   should be possible to take out a lock without also causing
   transmission of the contents of a resource.

   It is often necessary to guarantee that a lock or unlock operation
   occurs at the same time across multiple resources, a feature which is
   supported by the multiple-resource locking requirement. This is
   useful for preventing a collision between two people trying to
   establish locks on the same set of resources, since with multi-
   resource locking, one of the two people will get a lock. If this same
   multiple-resource locking scenario was repeated by using atomic lock
   operations iterated across the resources, the result would be a
   splitting of the locks between the two people, based on resource
   ordering and race conditions.

5.4. Reservations

5.4.1. Functional Requirements

   5.4.1.1. Reserve. It must be possible for a principal to register
   with the server an intent to edit a given resource, so that other
   principals can discover who intends to edit the resource.

   5.4.1.2. Reservation Query. It must be possible to find out whether a
   given resource has any active reservations, and if so, who currently
   holds reservations.

   5.4.1.3. Release Reservation.  It must be possible to release the
   reservation.

5.4.2. Rationale

   Experience from configuration management systems has shown that
   people need to know when they are about to enter a parallel editing
   situation. Once notified, they either decide not to edit in parallel
   with the other authors, or they use out-of-band communication (face-
   to-face, telephone, etc.) to coordinate their editing to minimize the
   difficulty of merging their results. Reservations are separate from
   locking, since a write lock does not necessarily imply a resource
   will be edited, and a reservation does not carry with it any access
   restrictions. This capability supports versioning, since a check-out
   typically involves taking out a write lock, making a reservation, and
   getting the resource to be edited.

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5.5. Retrieval of Unprocessed Source for Editing

5.5.1. Functional Requirement

   The source of any given resource must be retrievable by any principal
   with authorization to edit the resource.

5.5.2. Rationale

   There are many cases where the source stored on a server does not
   correspond to the actual entity transmitted in response to an HTTP
   GET. Current known cases are server side include directives, and
   Standard Generalized Markup Language (SGML) source which is converted
   on the fly to HyperText Markup Language (HTML) [HTML] output
   entities. There are many possible cases, such as automatic conversion
   of bitmap images into several variant bitmap media types (e.g. GIF,
   JPEG), and automatic conversion of an application's native media type
   into HTML. As an example of this last case, a word processor could
   store its native media type on a server which automatically converts
   it to HTML. A GET of this resource would retrieve the HTML.
   Retrieving the source would retrieve the word processor native
   format.

5.6. Partial Write.

5.6.1. Functional Requirement

   After editing a resource, it must be possible to write only the
   changes to the resource, rather than retransmitting the entire
   resource.

5.6.2. Rationale

   During distributed editing which occurs over wide geographic
   separations and/or over low bandwidth connections, it is extremely
   inefficient and frustrating to rewrite a large resource after minor
   changes, such as a one-character spelling correction. Support is
   needed for transmitting "insert" (e.g., add this sentence in the
   middle of a document) and "delete" (e.g. remove this paragraph from
   the middle of a document) style updates. Support for partial resource
   updates will make small edits more efficient, and allow distributed
   authoring tools to scale up for editing large documents.

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5.7. Name Space Manipulation

5.7.1. Copy

5.7.1.1. Functional Requirements

   It must be possible to duplicate a resource without a client loading,
   then resaving the resource. After the copy operation, a modification
   to either resource must not cause a modification to the other.

5.7.1.2. Rationale

   There are many reasons why a resource might need to be duplicated,
   such as changing ownership, preparing for major modifications, or
   making a backup. Due to network costs associated with loading and
   saving a resource, it is far preferable to have a server perform a
   resource copy than a client.

5.7.2. Move/Rename

5.7.2.1. Functional Requirements

   It must be possible to change the location of a resource without a
   client loading, then resaving the resource under a different name.
   After the move operation, it must no longer be possible to access the
   resource at its original location.

5.7.2.2. Rationale

   It is often necessary to change the name of a resource, for example
   due to adoption of a new naming convention, or if a typing error was
   made entering the name originally. Due to network costs, it is
   undesirable to perform this operation by loading, then resaving the
   resource, followed by a delete of the old resource. Similarly, a
   single rename operation is more efficient than a copy followed by a
   delete operation.  Note that moving a resource is considered the same
   function as renaming a resource.

5.8. Collections

   A collection is a resource that is a container for other resources,
   including other collections.  A resource may belong to a collection
   either directly or by reference.  If a resource belongs to a
   collection directly, name space operations like copy, move, and
   delete applied to the collection also apply to the resource.  If a
   resource belongs to a collection by reference, name space operations
   applied to the collection affect only the reference, not the resource
   itself.

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5.8.1. Functional Requirements

   5.8.1.1. List Collection. A listing of all resources in a specific
   collection must be accessible.

   5.8.1.2. Make Collection. It must be possible to create a new
   collection.

   5.8.1.3. Add to Collection.  It must be possible to add a resource to
   a collection directly or by reference.

   5.8.1.4. Remove from Collection.  It must be possible to remove a
   resource from a collection.

5.8.2. Rationale

   In [URL] it states that, "some URL schemes (such as the ftp, http,
   and file schemes) contain names that can be considered hierarchical."
   Especially for HTTP servers which directly map all or part of their
   URL name space into a filesystem, it is very useful to get a listing
   of all resources located at a particular hierarchy level. This
   functionality supports "Save As..." dialog boxes, which provide a
   listing of the entities at a current hierarchy level, and allow
   navigation through the hierarchy. It also supports the creation of
   graphical visualizations (typically as a network) of the hypertext
   structure among the entities at a hierarchy level, or set of levels.
   It also supports a tree visualization of the entities and their
   hierarchy levels.

   In addition, document management systems may want to make their
   documents accessible through the Web.  They typically allow the
   organization of documents into collections, and so also want their
   users to be able to view the collection hierarchy through the Web.

   There are many instances where there is not a strong correlation
   between a URL hierarchy level and the notion of a collection. One
   example is a server in which the URL hierarchy level maps to a
   computational process which performs some resolution on the name. In
   this case, the contents of the URL hierarchy level can vary depending
   on the input to the computation, and the number of resources
   accessible via the computation can be very large. It does not make
   sense to implement a directory feature for such a name space.
   However, the utility of listing the contents of those URL hierarchy
   levels which do correspond to collections, such as the large number
   of HTTP servers which map their name space to a filesystem, argue for
   the inclusion of this capability, despite not being meaningful in all

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   cases. If listing the contents of a URL hierarchy level does not
   makes sense for a particular URL, then a "405 Method Not Allowed"
   status code could be issued.

   The ability to create collections to hold related resources supports
   management of a name space by packaging its members into small,
   related clusters. The utility of this capability is demonstrated by
   the broad implementation of directories in recent operating systems.
   The ability to create a collection also supports the creation of
   "Save As..." dialog boxes with "New Level/Folder/Directory"
   capability, common in many applications.

5.9. Versioning

5.9.1. Background and General Principles

   5.9.1.1. Stability of versions. Most versioning systems are intended
   to provide an accurate record of the history of evolution of a
   document. This accuracy is ensured by the fact that a version
   eventually becomes "frozen" and immutable. Once a version is frozen,
   further changes will create new versions rather than modifying the
   original. In order for caching and persistent references to be
   properly maintained, a client must be able to determine that a
   version has been frozen. Any successful attempt to retrieve a frozen
   version of a resource will always retrieve exactly the same content,
   or return an error if that version (or the resource itself) is no
   longer available.

   5.9.1.2. Operations for Creating New Versions.  Version management
   systems vary greatly in the operations they require, the order of the
   operations, and how they are combined into atomic functions.  In the
   most complete cases, the logical operations involved are:

        o Reserve existing version
        o Lock existing version
        o Retrieve existing version
        o Request or suggest identifier for new version
        o Write new version
        o Release lock
        o Release reservation

   With the exception of requesting a new version identifier, all of
   these operations have applications outside of versioning and are
   either already part of HTTP or are discussed in earlier sections of
   these requirements. Typically, versioning systems combine
   reservation, locking, and retrieval -- or some subset of these --
   into an atomic checkout function.  They combine writing, releasing

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   the lock, and releasing the reservation -- or some subset of these --
   into an atomic checkin function.  The new version identifier may be
   assigned either at checkout or at checkin.

   The WebDAV extensions must find some balance between allowing
   versioning servers to adopt whatever policies they wish with regard
   to these operations and enforcing enough uniformity to keep client
   implementations simple.

   5.9.1.3. The Versioning Model.  Each version typically stands in a
   "derived from" relationship to its predecessor(s).  It is possible to
   derive several different versions from a single version (branching),
   and to derive a single version from several versions (merging).
   Consequently, the collection of related versions forms a directed
   acyclic graph.  In the following discussion, this graph will be
   called a "version graph".  Each node of this graph is a "version" or
   "member of the version graph".  The arcs of the graph capture the
   "derived from" relationships.

   It is also possible for a single resource to participate in multiple
   version graphs.

   The WebDAV extensions should support this versioning model, though
   particular servers may restrict it in various ways.

   5.9.1.4. Versioning Policies. Many writers, including Feiler [CM] and
   Haake and Hicks [VSE], have discussed the notion of versioning styles
   (referred to here as versioning policies, to reflect the nature of
   client/server interaction) as one way to think about the different
   policies that versioning systems implement. Versioning policies
   include decisions on the shape of version histories (linear or
   branched), the granularity of change tracking, locking requirements
   made by a server, etc. The protocol should clearly identify the
   policies that it dictates and the policies that are left up to
   versioning system implementors or administrators.

   5.9.1.5. It is possible to version resources of any media type.

5.9.2. Functional Requirements

   5.9.2.1. Referring to a version graph. There must be a way to refer
   to a version graph as a whole.

   Some queries and operations apply, not to any one member of a version
   graph, but to the version graph as a whole.  For example, a client
   may request that an entire graph be moved, or may ask for a version
   history. In these cases, a way to refer to the whole version graph is
   required.

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   5.9.2.2. Referring to a specific member of a version graph. There
   must be a way to refer to each member of a version graph. This means
   that each member of the graph is itself a resource.

   Each member of a version graph must be a resource if it is to be
   possible for a hypertext link to refer to specific version of a page,
   or for a client to request a specific version of a document for
   editing.

   5.9.2.3. A client must be able to determine whether a resource is a
   version graph, or whether a resource is itself a member of a version
   graph.

   A resource may be a simple, non-versioned resource, or it may be a
   version graph, or it may be a member of a version graph.  A client
   needs to be able to tell which sort of resource it is accessing.

   5.9.2.4. There must be a way to refer to a server-defined default
   member of a version graph.

   The server should return a default version of a resource for requests
   that ask for the default version, as well as for requests where no
   specific version information is provided. This is one of the simplest
   ways to guarantee non-versioning client compatibility. This does not
   rule out the possibility of a server returning an error when no
   sensible default exists.

   It may also be desirable to be able to refer to other special members
   of a version graph. For example, there may be a current version for
   editing that is different from the default version.  For a graph with
   several branches, it may be useful to be able to request the tip
   version of any branch.

   5.9.2.5. It must be possible, given a reference to a member of a
   version graph, to find out which version graph(s) that resource
   belongs to.

   This makes it possible to understand the versioning context of the
   resource. It makes it possible to retrieve a version history for the
   graphs to which it belongs, and to browse the version graph. It also
   supports some comparison operations: It makes it possible to
   determine whether two references designate members of the same
   version graph.

   5.9.2.6. Navigation of a version graph.  Given a reference to a
   member of a version graph, it must be possible to discover and access
   the following related members of the version graph.

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        o root member of the graph
        o predecessor member(s)
        o successor member(s)
        o default member of the graph

   It must be possible in some way for a versioning client to access
   versions related to a resource currently being examined.

   5.9.2.7. Version Topology. There must be a way to retrieve the
   complete version topology for a version graph, including information
   about all members of the version graph. The format for this
   information must be standardized so that the basic information can be
   used by all clients. Other specialized formats should be
   accommodated, for servers and clients that require information that
   cannot be included in the standard topology.

   5.9.2.8. A client must be able to propose a version identifier to be
   used for a new member of a version graph. The server may refuse to
   use the client's suggested version identifier.  The server should
   tell the client what version identifier it has assigned to the new
   member of the version graph.

   5.9.2.9. A version identifier must be unique across a version graph.

   5.9.2.10. A client must be able to supply version-specific properties
   to be associated with a new member of a version graph. (See Section
   5.1 "Properties" above.) At a minimum, it must be possible to
   associate comments with the new member, explaining what changes were
   made.

   5.9.2.11. A client must be able to query the server for information
   about a version tree, including which versions are locked, which are
   reserved for editing, and by whom (Session Tracking).

5.9.3. Rationale

   Versioning in the context of the world-wide web offers a variety of
   benefits:

   It provides infrastructure for efficient and controlled management of
   large evolving web sites. Modern configuration management systems are
   built on some form of repository that can track the revision history
   of individual resources, and provide the higher-level tools to manage
   those saved versions. Basic versioning capabilities are required to
   support such systems.

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   It allows parallel development and update of single resources. Since
   versioning systems register change by creating new objects, they
   enable simultaneous write access by allowing the creation of variant
   versions. Many also provide merge support to ease the reverse
   operation.

   It provides a framework for coordinating changes to resources. While
   specifics vary, most systems provide some method of controlling or
   tracking access to enable collaborative resource development.

   It allows browsing through past and alternative versions of a
   resource.  Frequently the modification and authorship history of a
   resource is critical information in itself.

   It provides stable names that can support externally stored links for
   annotation and link-server support. Both annotation and link servers
   frequently need to store stable references to portions of resources
   that are not under their direct control. By providing stable states
   of resources, version control systems allow not only stable pointers
   into those resources, but also well-defined methods to determine the
   relationships of those states of a resource.

   It allows explicit semantic representation of single resources with
   multiple states. A versioning system directly represents the fact
   that a resource has an explicit history, and a persistent identity
   across the various states it has had during the course of that
   history.

5.10. Variants

   Detailed requirements for variants will be developed in a separate
   document.

5.10.1. Functional Requirements

   It must be possible to send variants to the server, describing the
   relationships between the variants and their parent resource.  In
   addition, it must be possible to write and retrieve variants of
   property labels, property descriptions, and property values.

5.10.2. Rationale

   The HTTP working group is addressing problems of content negotiation
   and retrieval of variants of a resource.  To extend this work to an
   authoring environment, WEBDAV must standardize mechanisms for authors
   to use when submitting variants to a server.  Authors need to be able
   to provide variants in different file or document formats, for
   different uses. They need to provide variants optimized for different

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   clients and for different output devices.  They need to be able to
   provide variants in different languages in the international
   environment of the Web.  In support of internationalization
   requirements (See 5.12 below), variants need to be supported not just
   for the content of resources, but for any information intended for
   human use, such as property values, labels, and descriptions.

5.11. Security

   5.11.1. Authentication. The WebDAV specification should state how the
   WebDAV extensions interoperate with existing authentication schemes,
   and should make recommendations for using those schemes.

   5.11.2. Access Control. Access control requirements are specified in
   a separate access control work in progress [AC].

   5.11.3. Interoperability with Security Protocols. The WebDAV
   specification must provide a minimal list of security protocols which
   any compliant server / client must support.  These protocols should
   insure the authenticity of messages and the privacy and integrity of
   messages in transit.

5.12. Internationalization

5.12.1. Character Sets and Languages

   Since Web distributed authoring occurs in a multi-lingual
   environment, information intended for user comprehension must conform
   to the IETF Character Set Policy [CHAR].  This policy addresses
   character sets and encodings, and language tagging.

5.12.2. Rationale

   In the international environment of the Internet, it is important to
   insure that any information intended for user comprehension can be
   displayed in a writing system and language agreeable to both the
   client and the server. The information encompassed by this
   requirement includes not only the content of resources, but also such
   things as display names and descriptions of properties, property
   values, and status messages.

6. Acknowledgements

   Our understanding of these issues has emerged as the result of much
   thoughtful discussion, email, and assistance by many people, who
   deserve recognition for their effort.

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   Terry Allen, tallen@sonic.net
   Alan Babich, FileNet, babich@filenet.com
   Dylan Barrell, Open Text, dbarrell@opentext.ch
   Barbara Bazemore, PC DOCS, barbarab@pcdocs.com
   Martin Cagan, Continuus Software, Marty_Cagan@continuus.com
   Steve Carter, Novell, srcarter@novell.com
   Dan Connolly, World Wide Web Consortium, connolly@w3.org
   Jim Cunningham, Netscape, jfc@netscape.com
   Ron Daniel Jr., Los Alamos National Laboratory, rdaniel@lanl.gov
   Mark Day, Lotus, Mark_Day@lotus.com
   Martin J. Duerst, mduerst@ifi.unizh.ch
   Asad Faizi, Netscape, asad@netscape.com
   Ron Fein, Microsoft, ronfe@microsoft.com
   David Fiander, Mortice Kern Systems, davidf@mks.com
   Roy Fielding, U.C. Irvine, fielding@ics.uci.edu
   Mark Fisher, Thomson Consumer Electronics, FisherM@indy.tce.com
   Yaron Y. Goland, Microsoft, yarong@microsoft.com
   Phill Hallam-Baker, MIT, hallam@ai.mit.edu
   Dennis Hamilton, Xerox PARC, hamilton@parc.xerox.com
   Andre van der Hoek, University of Colorado, Boulder,
     andre@cs.colorado.edu
   Del Jensen, Novell, dcjensen@novell.com
   Gail Kaiser, Columbia University, kaiser@cs.columbia.edu
   Rohit Khare, World Wide Web Consortium, khare@w3.org
   Ora Lassila, Nokia Research Center, ora.lassila@research.nokia.com
   Ben Laurie, A.L. Digital, ben@algroup.co.uk
   Mike Little, Bellcore, little@bellcore.com
   Dave Long, America Online, dave@sb.aol.com
   Larry Masinter, Xerox PARC, masinter@parc.xerox.com
   Murray Maloney, SoftQuad, murray@sq.com
   Jim Miller, World Wide Web Consortium, jmiller@w3.org
   Howard S. Modell, Boeing, howard.s.modell@boeing.com
   Keith Moore, University of Tennessee, Knoxville, moore@cs.utk.edu
   Henrik Frystyk Nielsen, World Wide Web Consortium, frystyk@w3.org
   Jon Radoff, NovaLink, jradoff@novalink.com
   Alan Robertson, alanr@bell-labs.com
   Henry Sanders, Microsoft,
   Andrew Schulert, Microsoft, andyschu@microsoft.com
   Christopher Seiwald, Perforce Software, seiwald@perforce.com
   Einar Stefferud, stef@nma.com
   Richard Taylor, U.C. Irvine, taylor@ics.uci.edu
   Robert Thau, MIT, rst@ai.mit.edu
   Sankar Virdhagriswaran, sv@hunchuen.crystaliz.com
   Dan Whelan, FileNet, dan@FILENET.COM
   Gregory J. Woodhouse, gjw@wnetc.com

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7. References

   [AC] J. Radoff, "Requirements for Access Control within Distributed
   Authoring and Versioning Environments on the World Wide Web",
   unpublished manuscript, <http://lists.w3.org/Archives/Public/w3c-
   dist-auth/1997AprJun/0183.html>

   [CHAR] Alvestrand, H., "IETF Policy on Character Sets and Languages",
   RFC 2277, January 1998.

   [CM] P. Feiler, "Configuration Management Models in Commercial
   Environments", Software Engineering Institute Technical Report
   CMU/SEI-91-TR-7,
   <http://www.sei.cmu.edu/products/publications/91.reports/91.tr.007.html>

   [HTML] Berners-Lee, T., and  D. Connolly, "HyperText Markup Language
   Specification - 2.0", RFC 1866, November 1995.

   [HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
   Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,
   January 1997.

   [ISO 10646] ISO/IEC 10646-1:1993. "International Standard --
   Information Technology -- Universal Multiple-Octet Coded Character
   Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane."

   [URL] Berners-Lee, T., Masinter, L., and M. McCahill. "Uniform
   Resource Locators (URL)", RFC 1738, December 1994.

   [VSE] A. Haake, D. Hicks, "VerSE: Towards Hypertext Versioning
   Styles", Proc. Hypertext'96, The Seventh ACM Conference on Hypertext,
   1996, pages 224-234.

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8. Authors' Addresses

   Judith Slein
   Xerox Corporation
   800 Phillips Road 128-29E
   Webster, NY 14580

   EMail: slein@wrc.xerox.com

   Fabio Vitali
   Department of Computer Science
   University of Bologna
   ITALY

   EMail: fabio@cs.unibo.it

   E. James Whitehead, Jr.
   Department of Information and Computer Science
   University of California
   Irvine, CA 92697-3425

   Fax: 714-824-4056
   EMail: ejw@ics.uci.edu

   David G. Durand
   Department of Computer Science
   Boston University
   Boston, MA

   EMail: dgd@cs.bu.edu

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9.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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