CS789, Spring 2005, Lecture notes, Week 10

CS789, Spring 2005

Lecture notes, Week 10


I don't know what it is, but I know it when I don't see it.

Context is `all the rest': the things that aren't stated explicitly.

What's important about context?

  1. Synchronization of context is essential for communication.
  2. Building context is a slow process, and requires slow changes.

    Context depends on continuity: in time, in space.

  3. Context is really big.
  4. It depends on memory.

State and History


Why is memory important?

  1. Mode of user access to interfaces
  2. Foundation of context, which interacts with perception to inform us about the world
Memory is Really, there's no such thing as memory; there's just how you brain happens to be, right now. But how it is right now is conditioned by what happened in the past. Memory also exists outside the brain Notice how this memory involves inference.

What are the components of memory?

  1. Immediate sensory store
  2. Short-term memory
  3. Long-term store

There is an extremely subtle interaction between perception and memory

Our goal in the interface is
  1. to make external augmentations of memory as effective as memory itself

    You say Google: what's the correct response?

  2. to make new windows into the world as effortless to use as direct perception

    You say `videoconference': what's the correct response?


Navigation has three components

  1. knowing where you are,
  2. knowing where you want to be, and
  3. knowing how to get from here to there.

How does a user know where he or she is? How does a user know the current context?

  1. Dead reckoning
  2. Location finding Note that landmarks have to be associated with a map: of what to what?

Two styles of interface

  1. History-oriented: system presents history, user constructs state
  2. State-oriented: system presents state, user remembers history
In the real world what happens
  1. Perception shows us some of the state, as it exists right now.
  2. Memory retains state as it existed at particular times in the past. Sometimes memory is transformed to make it more like the future. Memory is not a very reliable guide to what things are like right now, but it's a lot better than nothing.
  3. Perception interacts with memory to bring things up to date. How much of this process needs attention? Not much.
  4. What happens when significant inconsistencies are detected between memory and perception?

Tests for interface style

  1. Canonical
  2. Suppose you are editting a file,
  3. Suppose you are reading mail,
  4. Most systems are hybrids, but close to one or the other.

Essential characteristics

Illustrative examples

How do users use this information?

Characteristic strengths of history-oriented interfaces

Characteristic strengths of state-oriented interfaces

Important crutches for history-oriented interfaces

The general prinicple behind this idea is that we recover from errors in one of two ways
  1. by teleportation to a well-known place
  2. by reversing the last change(s) to get back to a state we remember
Multiple reverses tend to be unpredictable, because our memory of exactly how things were doesn't extend very far.

Important crutches for state-oriented interfaces


In a given context do a sequence of operations

Users write programs in scripting languages






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