Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/drafts/draft_ietf_u_z/draft-ietf-webdav-requirements-00.txt

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WEBDAV Working Group                J.A. Slein
INTERNET-DRAFT                      Xerox Corporation
<draft-ietf-webdav-requirements-00.txt>        F. Vitali
                        University of Bologna
                        E.J. Whitehead, Jr.
                        U.C. Irvine
                        D.G. Durand
                        Boston University
                        May 30, 1997

Expires November 30, 1997

     Requirements for Distributed Authoring and Versioning
                    on the World Wide Web


Status of this Memo

This document is an Internet draft. Internet drafts are working
documents of the Internet Engineering Task Force (IETF), its areas and
its working groups. Note that other groups may also distribute working
information as Internet drafts.

Internet Drafts are draft documents valid for a maximum of six months
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Distribution of this document is unlimited. Please send comments to the
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http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth/.

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
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

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This document describes functionality which, if incorporated in an
extension to the existing HTTP proposed standard [4], 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 possible that a
single mechanism could simultaneously satisfy several requirements.

This document is intended to reflect the consensus of the WWW
Distributed Authoring and Versioning working group (WebDAV) as to the
functionality that needs to be standardized to support distributed
authoring and versioning on the Web. However, this version still has
some elements that are being debated in the working group. The following
elements are still under discussion:

    o Whether support for multi-resource locking is needed
    o Whether reservations should be treated as shared or advisory
      locks
    o What requirements there should be for access control
    o What requirements there should be for internationalization
    o How far WebDAV should be concerned about compatibility with
      other transport protocols besides HTTP

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:

    Attributes
    Links
    Locking

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    Reservations
    Retrieval of Unprocessed Source
    Partial Write
    Name Space Manipulation
    Collections
    Versioning
    Security
    Internationalization

3. Terminology

Where there is overlap, usage is intended to be consistent with that in
the HTTP 1.1 specification [4].

Attribute
    Named descriptive information about a resource.

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 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.

Reservation
    A declaration to the server that one intends to edit a resource.

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

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Server
    A program which receives and responds to HTTP requests.

Server Attribute
    An attribute whose value is generated by the server.

User Agent
    The client that initiates a request.

User Attribute
    An attribute whose value is provided by a user or a user agent.

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.

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 [2]. Special additional information should not become a
mandatory part of document formats.


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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.  Resources
may have attributes on different servers.  Any resources 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 metadata.  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: links,
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.

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 preculde 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. Attributes

5.1.1. Functional Requirements

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

5.1.2. Rationale

Attributes 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
attributes have many uses, such as supporting searches on attribute

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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, query, 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 connection 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 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 [1]. 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 re-reading 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 in the same 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 modification restrictions, and if so, who
currently has modification permission.

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

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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
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 to notify the server that
a resource is about to be edited by a given person.

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.

5.5. Retrieval of Unprocessed Source for Editing


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5.5.1. Functional Requirement

The source of any given resource must be retrievable.

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) [1] 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.

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, the content of
the destination resource must be octet for octet identical to the
content of the source resource. 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

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resource, it is far preferable to have a server perform a resource copy
than a client. If a copied resource records which resource it is a copy
of, then it would be possible for a cache to avoid loading the copied
resource if it already locally stores the original.

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, the content of the resource at its new
location must be octet for octet identical to the content of the prior
resource. 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, namespace operations like copy, move, and
delete applied to the collection also apply to the resource.  If a
resource belongs to a collection by reference, namespace operations
applied to the collection affect only the reference, not the resource
itself.

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 [2] it states that, "some URL schemes (such as the ftp, http, and

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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 namespace. 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
namespace to a filesystem, argue for the inclusion of this capability,
despite not being meaningful in all 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

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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 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 [3] and
Haake and Hicks [5], 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.


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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.

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

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of a version graph, it must be possible to discover and access the
following related members of the version graph.
   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 exhamined.

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 accomodated, 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 metadata to
be associated with a new member of a version graph. (See Section 5.1
"Attributes" 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.

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.

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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. Security

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

5.10.2. Access Control. Access control requirements are TBD, and may
eventually be specified in a separate access control draft.

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

5.11. Internationalization

Internationalization requirements are TBD.

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.

Dylan Barrell, Open Text, [e-mail]
Barbara Bazemore, PC DOCS, [e-mail]
Martin Cagan, Continuus Software, [e-mail]
Steve Carter, Novell, [e-mail]
Dan Connolly, World Wide Web Consortium, [e-mail]
Jim Cunningham, Netscape, [e-mail]
Ron Daniel Jr., Los Alamos National Laboratory, [e-mail]
Mark Day, Lotus, [e-mail]
Asad Faizi, Netscape, [e-mail]
Ron Fein, Microsoft, [e-mail]
David Fiander, Mortice Kern Systems, [e-mail]
Roy Fielding, U.C. Irvine, [e-mail]

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draft-slein-www-dist-author-00.txt   WebDAV Requirements   February 1997

Mark Fisher, [e-mail]
Yaron Y. Goland, Microsoft, [e-mail]
Phill Hallam-Baker, MIT, [e-mail]
Dennis Hamilton, Xerox PARC, [e-mail]
Andre van der Hoek, University of Colorado, Boulder,
  [e-mail]
Del Jensen, Novell, [e-mail]
Gail Kaiser, Columbia University, [e-mail]
Rohit Khare, World Wide Web Consortium, [e-mail]
Mike Little, Bellcore, [e-mail]
Dave Long, America Online, [e-mail]
Henrik Frystyk Nielsen, World Wide Web Consortium, [e-mail]
Ora Lassila, Nokia Research Center, [e-mail]
Larry Masinter, Xerox PARC, [e-mail]
Murray Maloney, SoftQuad, [e-mail]
Jim Miller, World Wide Web Consortium, [e-mail]
Keith Moore, University of Tennessee, Knoxville, [e-mail]
Jon Radoff, NovaLink, [e-mail]
Alan Robertson, [e-mail]
Andrew Schulert, Microsoft, [e-mail]
Christopher Seiwald, Perforce Software, [e-mail]
Einar Stefferud, [e-mail]
Richard Taylor, U.C. Irvine, [e-mail]
Robert Thau, MIT, [e-mail]
Sankar Virdhagriswaran, [e-mail]
Gregory J. Woodhouse, [e-mail]

7. References

[1] T. Berners-Lee, D. Connolly, "HyperText Markup Language
Specification - 2.0", RFC 1866, MIT/LCS, November 1995.

[2] T. Berners-Lee, L. Masinter, M. McCahill. "Uniform Resource
Locators (URL)", RFC 1738, CERN, Xerox PARC, University of Minnesota,
December 1994.

[3] 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>

[4] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, and
T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,
U.C. Irvine, DEC, MIT/LCS, January 1997.

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

8. Authors' Addresses

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

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EMail: [e-mail]

Fabio Vitali
Department of Computer Science
University of Bologna
ITALY

EMail: [e-mail]

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

Fax: [phone]
EMail: [e-mail]

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

EMail: [e-mail]

Expires November 30, 1997

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