WebDAV Design Overview

1
WebDAVDesign Overview

• Munich IETF
• August 11, 1997

2
Properties Chunk Size

• Properties are small chunks of data describing
  a resource
• large chunks of descriptive data are stored as
  full resources, using a link to capture the
  relationship between the described and describing
  resources.
• Benefits
• Both large and small descriptive information can
  be accommodated
• More frequently accessed small-chunk data is more
  efficient than large chunk data

3
Properties Naming

• Properties are (name, value) pairs
• Property names are URIs
• can be a URL (no registration needed)
• can be a URI (register new URI scheme)
• Benefits
• Due to ownership of a domain name, URLs provide
  globally unique names without registration
• URLs allow rapid development and deployment of
  new schemas
• Stable, long-lifetime schemas can be named with a
  URI scheme, which is registered with IANA

4
Properties Name/Instance Distinction

• A property name URI names the syntax and
  semantics of the property.
• live properties server maintains consistency
  by enforcing syntax and semantics
• non-live properties client enforces syntax and
  semantics (property may be inconsistent)
• Benefits
• server can provide properties with values it
  generates
• client can define new properties unknown to the
  server
• major benefit flexibility

5
Properties Value is XML element

• The value of a property is a well-formed XML
  (eXtended Markup Language) element
• XML is a subset of SGML
• XML specification is being developed by the W3C,
  is currently very stable, should be a W3C
  Recommendation later this year.
• Benefits
• i18n support XML supports ISO 10646 encoding of
  characters

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Properties PROPPATCH

• PROPPATCH method is used to create and remove
  properties from a resource
• Benefits
• simple method handles modification to the state
  of a property
• can modify several properties at once, with one
  network round trip

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Properties FINDPROP (SEARCH)

• FINDPROP retrieves a list of properties from a
  resource
• Benefits
• can retrieve several (all) properties with a
  single network round trip

8
Property URLs

• A server may provide a mapping of a property
  instance to a URL
• GET retrieves the value of a property
• DELETE removes a property
• Benefits
• allows use of HTTP methods on properties (as
  appropriate, e.g., COPY, GET, DELETE, )
• GET allows quick, direct access to property
  values (1 round trip, no request body needed)

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Links using Properties

• A link is a property
• XML elements defined in the WebDAV specification
  are used to describe the source and
  destination(s) of the link
• Benefits
• treats links like any other descriptive
  information
• allows creation of links (relationships) on any
  content type
• XML format allows extra descriptive information
  to be added to a link by using extra tags

10
Collections

• A collection is a set of URIs listing the member
  resources
• internal member resources are immediately
  relative URIs
• an immediately relative URI is a relative URI in
  which ../ is illegal, which must begin with
  ./ and which may contain only one other / at
  theend of the URI
• external members resources are absolute URIs
  which are not internal URIs
• Benefits
• Provides a resource type which can model file
  system directories and arbitrary collections of
  resources (which may be located on multiple
  servers)

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Direct Containment

• An internal member resource is directly contained
  by the collection
• server maintains containment relationship between
  collection and member
• if a resource is created (PUT), it is
  automatically added to the collection
• if a resource is deleted (DELETE), it is
  automatically removed from the collection
• Benefits
• membership of collections automatically updated
• allows existing RFC 2068 methods to work as-is

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Referential Containment

• An external member resource (symbolic link) is
  referentially contained by the collection
• server does not maintain the containment
  relationship between the collection and the
  member
• if the member is deleted or moved, the collection
  typically does not get updated
• if the moved/deleted resource and collections
  containing it as an external member are on the
  same server, an intelligent server could update
  collections it controls
• in the general case where the moved/deleted
  resource and the collection are on different
  servers, nothing can be done without a
  server-to-server protocol (out of scope for
  WebDAV)

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Collections MKCOL

• The MKCOL method creates a new collection
• MKCOL can be invoked with a request body
• No request body empty collection is created
• Request body media-type specific results
• primarily to reserve body for future capability
• Benefits
• a simple method is used to create a collection
• MKCOL method avoids problems with adding
  collection creation semantics to PUT

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Collections INDEX

• INDEX lists the members of a collection, along
  with selected properties
• Properties which must be returned by INDEX are
  IsCollection, Content-Type, Creation-Date,
  Last-Modified, DisplayName, Content-Language, and
  Etag (entity tag)
• Response is an XML document
• Response from INDEX is cacheable (and has an
  associated entity tag)

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INDEX Benefits

• Benefits of INDEX method
• allows discovery of members of a collection
• can be used by caches to efficiently validate all
  members of a collection with a single network
  round-trip
• provides Save As dialog box support
• XML return format provides extensibility for
  other properties (e.g. access control information)

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Collections ADDREF/DELREF

• ADDREF method adds an external member to a
  collection
• DELREF method removes an external member from a
  collection
• Benefits
• Simple methods for adding/removing external
  members from a collection, does not require a
  request body
• Separate methods support separate access control

17
Namespace Management COPY

• COPY method duplicates an HTTP resource, property
  or collection
• Recursive behavior for collections controlled by
  Depth header (a discussion issue)
• Copies are performed by-value
• Benefits
• allows duplication of resources without needing
  to transmit them over the wire twice.

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COPY Options

• Overwrite header can disable overwriting the
  destination
• Enforce-Live-Properties header lists properties
  which must be live on the destination or the copy
  must fail
• Duplicate-Properties header can disable copying
  of properties
• Benefits
• prevent overwriting of existing data
• fine-grain control over the copying of properties

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Namespace Management MOVE

• MOVE method is defined as a COPY followed by a
  DELETE of the old location
• All COPY options apply to MOVE as well
• Benefits
• allows the renaming of resources
• allows positioning the resource in a different
  location in the hierarchy
• method is performed without needing to transmit
  the resource over the wire twice
• more efficient than separate COPY and DELETE

20
Source Link

• Problem a GET of dynamic content retrieves the
  dynamically generated result, which is not
  suitable for authoring
• Solution a source link points to a location
  where the unprocessed source of the dynamic
  resource can be retrieved
• Benefits allows editing of server-side includes,
  CGI scripts, and other dynamic content