User Interface; Graphical User Interface;Jabber XMPP-Core

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User Interface Graphical User InterfaceJabber
XMPP-Core
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Communicating between two presence-aware entities

• XML Stream
• Starts with ltstreamgt
• Ends with lt/streamgt
• Stream is unidirectional but two streams
  allowed over one TCP connection
• initial stream and response stream
• XML Stanza
• the stuff (packets) of the stream
• presence, message, iq are the only upper-level
  types

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A basic session
C lt?xml version'1.0'?gt ltstreamstream
to'example.com' xmlns'jabberclient'
xmlnsstream'http//etherx.jabber.org/streams'
version'1.0'gt S lt?xml version'1.0'?gt
ltstreamstream from'example.com'
id'someid' xmlns'jabberclient'
xmlnsstream'http//etherx.jabber.org/streams'
version'1.0'gt ... encryption,
authentication, and resource binding ... C
ltmessage from'juliet_at_example.com'
to'romeo_at_example.net'
xmllang'en'gt C ltbodygtArt thou not Romeo,
and a Montague?lt/bodygt C lt/messagegt S
ltmessage from'romeo_at_example.net'
to'juliet_at_example.com'
xmllang'en'gt S ltbodygtNeither, fair saint,
if either thee dislike.lt/bodygt S lt/messagegt C
lt/streamstreamgt S lt/streamstreamgt
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A session gone bad
C lt?xml version'1.0'?gt ltstreamstream
to'example.com' xmlns'jabberclient'
xmlnsstream'http//etherx.jabber.org/streams'
version'1.0'gt S lt?xml version'1.0'?gt
ltstreamstream from'example.com'
id'someid' xmlns'jabberclient'
xmlnsstream'http//etherx.jabber.org/streams'
version'1.0'gt ... encryption,
authentication, and resource binding ... C
ltmessage xmllang'en'gt ltbodygtBad XML, no
closing body tag! lt/messagegt S
ltstreamerrorgt ltxml-not-well-formed
xmlns'urnietfparamsxmlnsxmpp-streams'/gt
lt/streamerrorgt S lt/streamstreamgt
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Motivating GUI via IM
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Email, Instant messages, chat

• Email send message based on name
• must know name, but can guess it.
• IM can only send message to buddy
• can have both sides agree to be buddies.
• Chat can only send message to room
• must connect to room to get messages

Asynchronous like computation
Semi-synchronous like interactive
Semi-synchronous like parallelism
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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

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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

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Hard vs Soft State

• Hard State server knows buddy list
• can send status of each buddy to requester
• Soft State client knows buddy list
• can ask status of each buddy
• But indirection always requires hard state

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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.

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Many disconnected pieces

• Client-Server protocol (messier than just this)
• Client code
• User Interface Code
• Semantics of interaction
• e.g. send only to published subscribed entities

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(No Transcript)
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User Interface

• Want 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 interface
• make big assumptions about h/w abilities
• not really independent of GUI

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Evolution
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Separating events from handlers

• Register handler for event
• Two different types of events
• within application
• within window system.
• Events connect the two pieces but are developed
  separately.

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Separation of GUI description

• Glade

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No semantic content

• why bad?
• no error correction