Previous Notes

Notes for CSG meeting: Topics to cover

WebDAV tutorial

• Use slides -- http://kahuna.osafoundation.org/~lisa/OSAF-webdav-tutorial-20040413.ppt

Standards

• CalSch WG -- Bob Morgan
• Launch of iCalendar mailing list: Calsify
• Launch of Python iCalendar/vCard parsing libraries: VObject
• Launch of CalDAV mailing list, discussion so far
• IMAP WG completing Annotate, LISTEXT, SORT -- important for Chandler

Sharing Architecture

• Publishing Item Collections
  • Upload data to publisher's WebDAV account
  • Simplest case: Publicly readable data
  • Eg: entire calendar as WebDAV collection, events as WebDAV resources
  • Export Chandler attributes as WebDAV resource properties
  • Long-term: use standard fromats for resource bodies (e.g. iCalendar, vCard, RFC822)

• Publish + Invite
  • Enter list of people invited to share my material
  • Send sharing invitations via email/XMPP
  • Each Chandler recipient sees "Accept/Ignore" when invitation is received in Chandler
  • Each non-chandler recipient sees HTTP URL - can download standard body representation
  • Publisher can see the list of invitees later -- re-issue invitations if necessary.

• Access Control
  • Simplest case: publisher uploaded data to own WebDAV account, so whatever that account is configured for, becomes the default access control.
  • E.g. Unix permissions model: owner can do all operations, group can do most operations. This works for many small workgroup situations.
  • More complex servers: support for WebDAV ACL standard needed
  • Long term: Chandler GUI to expose server's Access Control settings for entire collection or for individual resources

• "Subscribe", or Share from this URL: Synchronize
  • Terminology issue: "Subscribe" means to download/synchronize repeatedly via polling
  • Synchronization is needed for offline functionality
  • Can provide URL to publicly-readable calendar (e.g. SF Symphony; Avalon Meeting Room) and download any changes for offline viewing any time
  • WebDAV supports synchronization through ETags and PROPFIND
  • Proposals to improve WebDAV synchronization (higher performance): SyncML integration? Replication reports?

• Browse shared Collection
  • How similar is browsing to synchronizing? How different?
  • Is the cache for browsing just the same as synchronized content?
  • How to make browsing fast?
  • WebDAV supports browse by using PROPFIND to display only a summary view, before all the details are downloaded
  • Even better if WebDAV SEARCH becomes standardized -- a subset of the information from PROPFIND, only what's needed in current view rather than entire collection contents

• Sharing Circle
  • Different circle for each Item Collection or use same circle for multiple Item Collections
  • Each person with read/write access treated equally -- no default "winner" of conflicts
  • Each person's Chandler can synchronize local changes and do automated merges
  • Conflicts that can't be resolved by software are published as conflicts for anybody to deal with
  • Each person can see the sharing status of other people -- e.g. Leslie hasn't updated in 1 week (maybe she's gone on vacation?)

• Choice of properties vs. body
  • WebDAV represents database-style data through properties, leaving bodies empty.
  • WebDAV represents file-structured data through bodies, with minimal properties.
  • Can we pick one for calendaring or do we use both?
  • Property advantage: fast browsing, easy to make modifications to small piece --> multi-author support
  • Body advantage: Better synchronization support, better support for plain HTTP clients.
  • Can we do both? CalDAV approach to make server do both...
  • Can we do both? Chandler dogfood approach maybe make client do both...

• Property namespaces, property values, and iCalendar
  • WebDAV properties MUST have namespaces
  • DAV: namespace only for standard properties
  • This makes WebDAV nicely extensible
  • Server must preserve, COPY, MOVE even custom properties it doesn't recognize
  • Property values are either XML elements or XML text
  • Dates are XML Text but defined (in specifications) as
  • Proposal to do datatyping for WebDAV
  • If we want iCalendar data to be reflected in the properties (for fast browsing and multi-author support) then iCalendar data must have an XML mapping for value, plus a namespace

• Single Item Sharing
  • How to share a single event, single contact?
  • Feasible via email --> absolute broadest accessibility
  • Email to Chandler user: view as Event/Contact primarily (not as email)
  • Email to Chandler user: Replacements to item are recognized and treated as updates
  • Email to non-Chandler user: view standard representation (iCalendar or vEvent)
  • Email to non-Chandler user: Replacements are simply additional (later) copies
  • How is this different from an invitation, for events? Not very different...
  • Same mechanism for Contacts, Tasks, even as-yet-undefined resources
  • Why not do email sharing for more than one item? Too difficult, unreliable, coordination hard!

• XMPP Uses
  • Instant messaging
  • Use XMPP to see whether contacts are online/offline -- visible when viewing contact, email from contact, email to contact
  • Use XMPP, when available, to deliver Chandler<--> Chandler messages -- preferable to email
  • Define a way for WebDAV server to generate XMPP notifications on change events...

• XMPP as Event Notification Infrastructure
  • HTTP(WebDAV) and XMPP are complementary
  • HTTP is designed for the server to handle many requests from many clients scalably and securely -- some are straightforward content requests, some require processing
  • XMPP is designed for the client to handle many requests scalably and securely from a variety of sources -- some are straightforward user text messages, some are intended for handling by software agents
  • XMPP is only protocol that provides a way to address a specific software agent via a user: lisa@osafoundation.org/Chandler
  • XMPP Pub/sub model: http://www.jabber.org/jeps/jep-0060.html
  • User agent (Chandler) subscribes to events: presence notifications, calendar collection change notifications
  • Terminology: issue: "Subscribe" here means to ask for and receive stream of live events -- almost the opposite of synchronization via polling

• Extranet sharing
  • Certificates
  • Tickets

Into Westwood

• What is a Chandler Server? What are the requirements?
• How much of this do we build or buy?
• What tradeoffs do we make between usability (advanced features), time to release, security, interoperability?
• WebDAV servers: ACL support? Certificate support? SEARCH? DeltaV?
• IMAP servers: Annotate support? LISTEXT? ACL2?

The good news

• If we'd done something proprietary we'd have to invent all of this
• Backward compatibility (to down-level clients) very feasible in very many situations

-- LisaDusseault - 17 Aug 2004