The Cost-of-Knowledge Characteristic Function: Display Evaluation for Direct-Walk Dynamic Information Visualizations

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The Cost-of-Knowledge Characteristic
FunctionDisplay Evaluation for Direct-Walk
Dynamic Information Visualizations

• CHI 94
• Card, Pirolli, Mackinlay

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Concepts

• Information has cost structure
• Objective maximize information benefits per unit
  cost (cost time)
• Cost-of-Knowledge Characteristic Function
• Characterizes the effect of a design of dynamic
  display/human-computer dialogue on informations
  cost structure

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Cost-of-Knowledge Characteristic Function

• Improve productivity Less time or more output

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Case study

• Direct-walk interactive infoviz
• Navigate an information structure using mouse
  points/other direct manipulation methods
• Analyze 2 calendar programs Spiral Calendar vs.
  Suns CM
• Users 4 users for each study, 2 overlapping
• Task navigate to another day in calendar

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Steps To Construct Cost-of-Knowledge Function

• Use tasks that take different amount of time to
  obtain different amount of information
• Identify cost drivers for the tasks
• In Spiral Calendar of cycles to go through
• In CM of different steps
• Measure time taken to perform each task as cost
• Perform regression of time (cost) as dependent
  variable and cost drivers as independent
  variables
• Plot cost vs. amount of information that can be
  obtained

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Cost Drivers

• Spiral Calendar Number of display cycles
  (Century, Decade, Year, Month, Week, Day)
  selected
• Regression fn Time 3.3 3.5 Ncycles
• CM
• m point, menu pull-down, select
• P point select
• B press a button
• Regression fn Time 1.3 3.9 m 1.4 P 0.36
  B

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Spiral Calendar Result Computation
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Sun CM Result Computation
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Cost-of-Knowledge Functions
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Value of Tasks

• Values of tasks
• Frequency
• Importance
• Etc.
• Needs to weight tasks by their values
• Ex. Use probability density function to weight
  tasks by frequency of use
• PrneededD days ago0.34/(0.34D0.83)

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Expected Probability-Weighted Costs
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Summary

• More measurable/computable method to evaluate a
  design
• Know your priority/objective sometimes perceived
  speed is more important than actual speed
• Issues
• How to accurately identify and measure all cost
  drivers of a task, e.g. of items?
• What if there are more than one way to perform a
  specific task?

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The WebBook Web Forager An Information
Workspace for the World-Wide Web

• CHI 96
• Card, Robertson, and York

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WebBook Web Forager

• Two related designs
• WebBook - 3D interactive book of HTML pages
• Web Forager an application that puts WebBook
  and other objects in a 3D hierarchical workspace

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Based On

• Cost structure of information workspaces the
  web has a uniform cost structure
• Information foraging theory users often seek
  strategies to increase the encounter rates of
  relevant information
• Locality of reference users tend to interact
  repeatedly with small clusters of information,
  and therefore keeping the cost of accessing low

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Problems At That Time

• Hotlist still have to wait for slow access
  times, not tunable to a reasonably
  cost-structured workspace.
• Multiple windows slow users down since they
  overlap.
• Users can only be at one page while the way the
  users actually work with information is to have
  multiple pages simultaneously available at hand.

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WebBook

• Use book metaphor (animated 3D) next previous
  links analogous to books, familiar, effective
  display
• Any collection of preload pages
• Can be bookmarked, put on a shelf
• Various way to collect URLs relative-URL, Topic,
  Hot List, Search Reports

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Web Forager

• Explore the potential for rapid interaction with
  large number of pages
• Use gestures to increase speed with which objects
  can be moved around
• Focus on the web
• Use a structured model to design (CoKC Fn)
• 3 levels book/page ? air desk ? bookcase

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Web Forager
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Cost of Knowledge Characteristic Function for Web
Forager
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Comments

• Metaphor do they really take advantage of the
  affordances of a physical book and workspace?
  What might you lose from using this metaphor?
• Speed of retrieving a web page is becoming less
  an issue
• Current browsers might already be able to solve
  the problems posed by the authors (and even work
  better, perhaps!)

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Effective View Navigation

• CHI 97
• Furnas

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Effective View Navigation

• ContextNavigate an information structure by
  selecting something in the current view of the
  structure
• Problems
• Large structures
• Limited resources of space time
• Proposed RequirementsEffective View Navigation
  (EVN) Effective View Traversibility (EVT)
  View Navigability (VN)

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Terms

• View traversal iterative process of viewing,
  selecting, moving to it
• View navigation decide where to go next
• Logical graph logical structure of the
  information
• Viewing graph contains nodes that users see in
  current view

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EVT Requirements for Viewing Graphs

• EVT1 Small Views space constraint of
  outgoing links of any node relative to
  structures size must be small ? small Maximal
  Out-Degree (MOD)
• EVT2 Short paths time constraint
• the longest connecting path relative to
  structures size must be small ? small Diameter
  (DIA)
• EVT(G)(MOD(G),DIA(G))
• G viewing graph

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A Scrolling List
EVT(O(1), O(n))
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A Balanced Tree
EVT(O(1), O(log n))
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Improving EVT of a List

• More dimensions - multi-column list EVT(O(1),
  O(sqrt(n)))

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Improving EVT of a List

• Fisheye sampling EVT(O(log n), O(log n))
  allow jumping further, but larger view

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Improving EVT of a List

• Adding a tree EVT(O(1), O(log n)) create
  categorization?

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EVT Summary

• Present information in a representation that
  naturally supports EVT - tree
• To fix non-EVT logical structures
• Add long-distance links
• Glue with another complete EVT structure

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View Navigability (VN)

• Ability to find good paths to targets without
  error history-less

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Terms

• Outlink-info info associated with outlink of a
  node (enumeration or labeling)
• To-set all possible targets a link actually
  leads to
• Inferred-to-set targets that the outlink-info
  seem to indicate
• Residue/scent remote indication of a node/target
  
• Well-matched outlink info inferred-to-set
  implies to-set

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Illustration
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Strong Navigability Requirement

1. Outlink-info must be everywhere well-matched
2. Every node must have good residue at every other
   node
3. Outlink-info must be small, but need to describe
   the whole to-set, not just the next node (e.g.
   highway signs)
4. Semantic labeling that mirrors actual partition
   of to-sets

Targets share residue
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Good Example

• Systematic labeling of trees of hierarchy, i.e.
  biological taxonomy

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Non-Navigable Structure

• Completely unrelated/unstructured items
• Only works with enumeration
• Locally-related structure no good residue for
  things far away, e.g. WWW
• Combine query navigation

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Combining EVT VN

• Large scale semantics (structure with larger
  groups) work!
• Assume n nodes v links in the structure
• Small view diameter v should be small compared
  to n
• Average size of to-sets (n/v) should be large
• Carve up the semantics of the domain efficiently
  due to Small Diameter req.
• Small of intersections
• Balanced hierarchy

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Summary

• Effective view navigation
• Small views
• Reasonable of steps to move around
• Discoverable route to any target
• Do navigability requirements guarantee users to
  always find shortest paths?