WebDAV Collections Protocol

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WebDAV Collections Protocol

• Redmond, June 16, 1998

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Referential Member
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Strong Reference
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Weak Reference
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Creating Referential Members

• M-PUT /whitehead/dav/ HTTP/1.1
• Host www.ics.uci.edu
• Man "DAVColl-headers"
• Referential-Member spec08.ref
• Ref-Target http//www.ics.uci.edu/i-d/draft-web
  dav-protocol-08.txt
• Ref-Integrity T
• Position After requirements.html
• Content-Length 0

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Mandatory Extensions in HTTP Rationale

• HTTP servers ignore unrecognized headers
• We want requests to fail if the server doesnt
  recognize DAV headers
• PUT, MOVE, and COPY are affected
• 3 new methods vs. Mandatory Extensions

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Mandatory Extensions in HTTP Description

• M- method prefix causes old servers to fail the
  request
• Uniquely identify extension headers
• Label the extension headers as mandatory or
  optional
• Optionally assign namespace label to extension
  headers
• Use extension headers as usual

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Creating Referential Members (revised)

• ADDREF /whitehead/dav/ HTTP/1.1
• Host www.ics.uci.edu
• Referential-Member spec08.ref
• Ref-Target http//www.ics.uci.edu/i-d/draft-web
  dav-protocol-08.txt
• Ref-Integrity T
• Position After requirements.html
• Content-Length 0

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Deleting Referential Members

• Use the HTTP DELETE method
• No effect on target except for updates to its
  DAVrefsource property when a strong reference is
  deleted

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Listing Collection Members

• Use the DAV PROPFIND method
• Listing will include both internal and
  referential members
• If Depth infinity, the server SHOULD NOT (MUST
  NOT?) follow references into any collections to
  which they may refer

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Other Operations on Referential Members

• LOCK, PROPPATCH, MOVE, COPY affect the
  referential member, not its target resource
• Use M-MOVE and M-COPY to create a strong
  reference at the destination
• GET and PROPFIND retrieve the headers /
  properties of the referential member, not of its
  target resource

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Other Operations on Referential Members (revised)

• LOCK, PROPPATCH, MOVE, COPY affect the
  referential member, not its target resource
• Use MOVE and COPY with the Ref-Integrity header
  to create a strong reference at the destination
• GET and PROPFIND retrieve the headers /
  properties of the referential member, not of its
  target resource

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Operations on Target Resources

• Operations on targets have no effect on
  referential members except as needed to maintain
  referential integrity for strong references
• MOVE on target causes a strong references
  DAVreftarget property to be updated
• DELETE on target of a strong reference Server
  decides how to enforce referential integrity

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Ordered Collections
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Characteristics of Orderings

• At most 1 ordering per collection
• Client decides whether a collection is ordered
• If a collection is ordered, each collection
  member belongs to the ordering exactly once
• Only members of the collection can belong to its
  ordering
• orderingtype SHOULD point to a resource that
  describes the semantics of the ordering

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Manipulating Orderings

• Retrieve the current DAVordering property with
  PROPFIND
• Modify DAVordering with PROPPATCH
• Use the Position header with M-PUT, M-MOVE, or
  M-COPY to insert a member into the ordering at
  the time it is added to the collection

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Manipulating Orderings (revised)

• Retrieve the current DAVordering property with
  PROPFIND
• Modify DAVordering with PROPPATCH
• Use the Position header with PUT, MOVE, or COPY
  to insert a member into the ordering at the time
  it is added to the collection

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PROPPATCH Example

• PROPPATCH /coll-1/ HTTP/1.1
• Host www.foo.com
• Content-Type text/xml
• Content-Length xxxx
• lt?xml version1.0 ?gt
• lt?xmlnamespace nsDAV prefixD ?gt
• ltDpropertyupdategt
• ltDsetgt
• ltDpropgt
• ltDorderinggt
• ltDorderingtypegt
• lthrefgthttp//www.foo.com/semantics/s1.txtlt/h
  refgt
• lt/Dorderingtypegt
• lthrefgtmaplt/hrefgt
• lthrefgthistorylt/hrefgt
• lthrefgtculturelt/hrefgt
• lt/Dorderinggt
• lt/Dpropgt

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Position Header Example

• PUT /coll1/history HTTP/1.1
• Host www.foo.com
• Content-Type text/plain
• Content-Length xxxx
• Position After map
• ltentity bodygt

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Server Responsibilities

• Remove href from ordering when member is removed
  from collection
• Add href to ordering when member is added to
  collection
• At requested position if Position header is used
• At end of ordering otherwise
• Verify values of DAVordering submitted with
  PROPPATCH
• Respond to PROPFIND with ordered listing if
  collection is ordered

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Creating an Ordered Collection (proposal)

• Ordered header for use with MKCOL
• Value is URI of ordering semantics
• Example
• MKCOL /collection1/ HTTP/1.1
• Host www.foo.com
• Ordered http//www.foo.com/semantics/s1.txt

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Implementation Note (proposal)

• Recommend that clients follow Mandatory
  Extensions specification when they want method to
  fail if server doesnt recognize ordering headers
• Ordered header with MKCOL
• Position header with PUT, MOVE, or COPY
• Define URI for extension semantics
• DAVOrderedCollectionHeaders

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Issues

• MOVE or COPY a collection that has referential
  members
• MOVE or COPY an ordered collection
• Let client choose whether Ref-Integrity, Ordered,
  and Position headers are optional or mandatory?
• How to enforce referential integrity for requests
  to DELETE a target resource
• Potential problems for ordering requests without
  transactions
• PROPPATCH vs. headers for manipulating orderings?
  Or allow both?

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Information

• Draft protocol specification is at
• http//www.ics.uci.edu/ejw/authoring/collection/d
  raft-ietf-webdav-collection-protocol-00.txt
• Author can be reached at
• slein_at_wrc.xerox.com