1. WebDAV Design 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 encoding of characters

6. 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

7. 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)

9. 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)

11. 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

12. 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)

13. 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

14. 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)

15. 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)

16. 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.

18. 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

19. 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