user interface; graphical user interface;jabber xmpp- core
TRANSCRIPT
User Interface; Graphical User
Interface;Jabber XMPP-Core
6.893 Spring 2004: User Interface Larry Rudolph
Communicating between two
presence-aware entitiesXML Stream
Starts with <stream>
Ends with </stream>
Stream is unidirectional; but two streams allowed over one TCP connection
initial stream and response stream
XML Stanza
the stuff (packets) of the streampresence, message, iq are the only upper-level types
6.893 Spring 2004: User Interface Larry Rudolph
A basic sessionC: <?xml version='1.0'?> <stream:stream to='example.com' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>S: <?xml version='1.0'?> <stream:stream from='example.com' id='someid' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>... encryption, authentication, and resource binding ...C: <message from='[email protected]' to='[email protected]' xml:lang='en'>C: <body>Art thou not Romeo, and a Montague?</body>C: </message>S: <message from='[email protected]' to='[email protected]' xml:lang='en'>S: <body>Neither, fair saint, if either thee dislike.</body>S: </message>C: </stream:stream>S: </stream:stream>
6.893 Spring 2004: User Interface Larry Rudolph
A session gone badC: <?xml version='1.0'?> <stream:stream to='example.com' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>S: <?xml version='1.0'?> <stream:stream from='example.com' id='someid' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' version='1.0'>... encryption, authentication, and resource binding ...C: <message xml:lang='en'> <body>Bad XML, no closing body tag! </message>S: <stream:error> <xml-not-well-formed xmlns='urn:ietf:params:xml:ns:xmpp-streams'/> </stream:error>S: </stream:stream>
Motivating GUI via IM
Email, Instant messages, chat
Email: send message based on name
must know name, but can guess it.
IM: can only send message to buddycan have both sides agree to be buddies.
Chat: can only send message to “room”
must connect to “room” to get messages
Asynchronouslike “computation”
Semi-synchronouslike “interactive”
Semi-synchronouslike “parallelism”
Big Idea: Abstraction
“Any problem in computer programming can be solved by adding a level of abstraction”
“Performance can be improved in programs by removing a level of abstraction”
Indirection used to support abstraction
Big Idea for IM: Indirection
“Publish and subscribe” Publish “presence” with a server
Subscribe to relevant published entities
Once when registering and whenever logon
“Interact”direct communication
(mediated) indirect communication
Hard vs Soft State
Hard State: server knows buddy list
can send status of each buddy to requester
Soft State: client knows buddy listcan ask status of each buddy
But indirection always requires hard state
Instant Messaging
Clients register with server
When client logs on, others subscribe
Client sends message to server, server forwards to recipient
can only send messages to registered/published recipients
Supported operations:Register, Unregister, Logon, Logoff, Send/Rec, Add/Remove Buddy, etc.
Many disconnected
piecesClient-Server protocol (messier than just this)
Client code
User Interface Code
Semantics of interactione.g. send only to published & subscribed entities
User InterfaceWant to disconnect application from user interface
Application should work independent of UI
Character display and keyboard or fancier
main difference was number of columns and lines
Graphical user interfacemake big assumptions about h/w abilities
not really independent of GUI
Evolution
Separating events from
handlersRegister handler for event
Two different types of events:within application
within window system.
Events connect the two pieces but are developed separately.
Separation of GUI description
Glade
No semantic content
why bad? no error correction