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RE: New Requirements Draft

From: Yaron Goland <yarong@microsoft.com>
Date: Wed, 27 Aug 1997 11:03:23 -0700
Message-ID: <11352BDEEB92CF119F3F00805F14F485037BC1EB@RED-44-MSG.dns.microsoft.com>
To: "'Dylan Barrell'" <dbarrell@bb.opentext.com>, "'Judith Slein'" <slein@wrc.xerox.com>, w3c-dist-auth@w3.org
I can find nothing in the charter which states that WebDAV's goal is to
provide a way to create everything HTTP/1.1 can dish up.
		Yaron

> -----Original Message-----
> From:	Dylan Barrell [SMTP:dbarrell@bb.opentext.com]
> Sent:	Wednesday, August 27, 1997 9:14 AM
> To:	'Judith Slein'; w3c-dist-auth@w3.org; Yaron Goland
> Subject:	RE: New Requirements Draft
> 
> Yaron,
> 
> How do you justify the opinion that it is out of scope for this group?
> 
> WebDAV is supposed to define the standard for distrubuted authoring of
> sites whos content is to be served by an HTTP1.1 compliant server.
> HTTP 1.1 provides a standard mechanism for serving-up variants so
> defining a standard for distributed authoring of these variants seems
> to fit quite well within the charter of this group.
> 
> Cheers
> Dylan
> 
> ----------
> From: 	Yaron Goland[SMTP:yarong@microsoft.com]
> Sent: 	Dienstag, 26. August 1997 19:32
> To: 	'Judith Slein'; w3c-dist-auth@w3.org
> Subject: 	RE: New Requirements Draft
> 
> I strongly object to 5.11.2, with or without a warning that we can not
> find a satisfactory solution.
> 
> There is consensus that we wish to be able to lock multiple resources
> simultaneously, it just isn't clear if we can write up a satisfactory
> standard to meet this requirement.
> 
> However there is not consensus on dealing with variants. Many folks,
> myself included, believe that this is out of scope for the group and
> should not be a goal.
> 
> 		Yaron
> 
> > -----Original Message-----
> > From:	Judith Slein [SMTP:slein@wrc.xerox.com]
> > Sent:	Friday, August 22, 1997 1:09 PM
> > To:	w3c-dist-auth@w3.org
> > Subject:	New Requirements Draft
> > 
> > I've undertaken to provide another requirements draft by August 29.
> > Here is
> > what I intend to submit, barring objections from the group.
> > 
> > Here are the changes from the previous draft:
> > 
> > 1. Since we hope that this draft will be the basis of last call, I
> > have
> > taken out the open issues list.
> > 
> > 2. I have taken out the requirements for query on properties (5.1.1)
> > and
> > query on links (5.2.1).
> > 
> > 3. The requirement for multi-resource locking (5.3.1.2) remains
> > unchanged,
> > but we all understand that it may be impossible to find a
> satisfactory
> > implementation, in which case WEBDAV will not satisfy this
> > requirement.  If
> > the group would like, I can state this explicitly in 5.3.1.2.
> > 
> > 4. The character sets / language tagging requirement has been
> revised
> > so
> > that it simply references the IETF character set policy (5.11.1).
> > 
> > 5. I have added a requirement for support of language variants
> > (5.11.2).  As
> > with 3 above, the assumption is that we may be unable to find a
> > satisfactory
> > implementation for this requirement.  As with 3, I could state this
> > explicitly.
> > 
> > --Judy
> > 
> >
> =====================================================================
> > 
> > WEBDAV Working Group				J.A. Slein
> > INTERNET-DRAFT      				Xerox
> Corporation
> > <draft-ietf-webdav-requirements-02.txt>		F. Vitali
> > 						University of Bologna
> > 
> > 						E.J. Whitehead, Jr.
> > 						U.C. Irvine
> > 						D.G. Durand
> > 						Boston University
> > 						August 29, 1997
> > 
> > Expires February 28, 1998
> > 
> >      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
> > and can be updated, replaced or obsoleted by other documents at any
> > time. It is inappropriate to use Internet drafts as reference
> material
> > or to cite them as other than as "work in progress".
> > 
> > To learn the current status of any Internet draft please check the
> > "lid-abstracts.txt" listing contained in the Internet drafts shadow
> > directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
> > munnari.oz.au (Pacific Rim), ds.internic.net (US East coast) or
> > ftp.isi.edu (US West coast). Further information about the IETF can
> be
> > found at URL: http://www.ietf.org/
> > 
> > Distribution of this document is unlimited. Please send comments to
> > the
> > WWW Distributed Authoring and Versioning (WebDAV) mailing list,
> > <w3c-dist-auth@w3.org>, which may be joined by sending a message
> with
> > subject "subscribe" to <w3c-dist-auth-request@w3.org>. Discussions
> are
> > archived at URL:
> > 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
> > 
> > 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 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.
> > 
> > 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
> > 	Versioning
> > 	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.
> > 
> > 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.
> > 
> > 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 [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.
> > Resources
> > may have properties 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 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.
> > 
> > 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 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 [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 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 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
> 
> > 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.
> > 
> > 5.5. Retrieval of Unprocessed Source for Editing
> > 
> > 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) [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.
> > 
> > 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 
> > 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, 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.
> > 
> > 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 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 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.
> > 
> > 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.
> >    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.
> > 
> > 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. 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 specified 
> > in a separate access control draft [AC].
> > 
> > 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
> > 
> > 5.11.1. 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.
> > 
> > 5.11.2. Language Variants
> > 
> > The HTTP working group is addressing problems of content negotiation
> > and retrieval of variants of a resource.  In an authoring
> environment,
> > authors must also be able to send variants to the server, and to 
> > describe the relationships between variants and their parent
> resource.
> > In addition, it must be possible to write and retrieve variants of
> > property labels, property descriptions, and property values.
> > 
> > 5.11.3. 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.
> > 
> > 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
> > 
> > 7. References
> > 
> > [AC] J. Radoff, "Requirements for Access Control within 
> > Distributed Authoring and Versioning Environments on the World 
> > Wide Web".
> > 
> > [CHAR] H.T. Alvestrand, "IETF Policy on Character Sets and
> Languages",
> > 
> > June 1997, working draft, draft-alvestrand-charset-policy-00.txt.
> > 
> > [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.htm
> > l>
> > 
> > [HTML] T. Berners-Lee, D. Connolly, "HyperText Markup Language
> > Specification - 2.0", RFC 1866, MIT/LCS, November 1995.
> > 
> > [HTTP] 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.
> > 
> > [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] T. Berners-Lee, L. Masinter, M. McCahill. "Uniform Resource
> > Locators (URL)", RFC 1738, CERN, Xerox PARC, University of
> Minnesota,
> > 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.
> > 
> > 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
> > 
> > Expires February 28, 1998
> > Name:			Judith A. Slein
> > E-Mail:			slein@wrc.xerox.com
> > Internal Phone:  	8*222-5169
> > External Phone:		(716) 422-5169
> > Fax:			(716) 265-7133
> > MailStop:		105-50C
> 
> 
Received on Wednesday, 27 August 1997 15:21:24 GMT

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