CardDAV Address Book Sharing

Users of CardDAV often require a mechanism to share an address book with other users. Sharing address books is for the most part completely implemented using draft-pot-webdav-resource-sharing, but there are a few considerations specific to CardDAV to ensure that certain mechanisms still behaves as expected.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . When XML element types in the namespaces "DAV:" and "urn:ietf:params:xml:ns:caldav" are referenced in this document outside of the context of an XML fragment, the string "DAV:" and "CALDAV:" will be prefixed to the element type names respectively.

While the draft-pot-webdav-resource-sharing specification allows sharing of potentially any resource on a server, this specification only concerns itself with sharing address book collections, as defined in CardDAV. Sharing of resources other than address book collections is not addressed in this specification.

vCard are often distributed via email, and two users of a CardDAV might have a copy of the same vCard. When those two users now share an addressbook, they might end up with two vCards that describe the same person. Some address book user agents coalesce two vCards from different addressbooks to show up as one (merged) vCard to an end user. These clients SHOULD ensure that when an update is made to a merged vCard, all instances of that vCard are updated if the user agent has read-write access. In case two vCards have conflicting information, the information from the vCard with the highest value for the REV property should be used.