Design Guidelines for Effective WWW History Mechanisms Linda Tauscher and Saul Greenberg University of Calgary This talk accompanied a paper, and was presented at: Tauscher, L. and Greenberg, S. (1996) Design Guidelines for Effective WWW History Mechanisms. In Microsoft Workshop, Designing for the Web: Empirical Studies. Microsoft Corporation, Redmond, WA. October 30 ©Linda Tauscher & Saul Greenberg

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Overview n Introduction / Objectives n Data Collection n Results n Conditioning the Distribution n Design Guidelines n Conclusion

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Introduction n History mechanisms allow people to revisit pages viewed previously n History mechanisms can mitigate impact of: u vast amounts and poor structure of information u resource use u cognitive and physical navigation burdens n Current history mechanisms are based on ad-hoc approaches

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Objectives n Understand people’s revisitation patterns when navigating the WWW n Evaluate current approaches, validate successful solutions, suggest alternatives n Provide guidelines for effective browser history design

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Data Collection n Xmosaic 2.6 modified to capture user’s browsing activity n Volunteer participants used browser for 6 weeks n Participants were practiced Web users n Quantitative data derived from logs of 23 participants n Qualitative data gathered via interviews

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Results n Recurrence of Web page visits n Growth of URL vocabulary n Web page visit frequency as a function of distance n Frequency of URL accesses n Locality n Longest Repeated Sequences

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Recurrence of Web page visits n Recurrence rate R u probability that any URL visited is a repeat of a previous visit University of Calgary: R = 58% (  = 9%) University of Calgary: R = 58% (  = 9%) Catledge and Pitkow: R = 61% (  = 9%) Catledge and Pitkow: R = 61% (  = 9%) n Web browsing is a recurrent system u users predominately repeat activities invoked before (Greenberg, 1993)

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Growth of URL vocabulary n URL vocabulary u number of unique URLs visited thus far vs. number of total URLs visited n Findings u users incorporate new URLs into their repertoire at a regular rate u revisits fairly evenly distributed u local variations highlight browsing patterns

URL Vocabulary for participant 15

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Web page visit frequency as a function of distance n Distance determined by u no. of items between current URL being visited from its first match on the history list n Recency effect u previous 6 or so URLs contribute the majority of pages visited next

URL recurrence rate as a function of distance (all participants) R as running sum

Frequency of URL visits for all participants

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Conditioning the Distribution n Objectives u increase recurrence probabilities over a set of a given size u evaluate methods currently in use n Method categories u recency ordered history lists u frequency ordered history lists u stack-based approaches u hierarchically structured history lists

Cumulative probabilities of recurrences over distances up to 50 R D10

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #1 n Maintain records of URLs visited, and allow users to recall previous URLs from those records u Web browsing is a recurrent system (R = 58%) u a history mechanism has value

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #2 n It should be cheaper, in terms of physical and cognitive activity, for users to recall URLs from a history mechanism than to navigate to them via other methods u attempt to predict the next URL selection u clearly distinguish the best predictions u minimize the number of physical actions to retrieve URL from history u provide clues to Web space structure

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #3 n A selectable history list of the previous 10 URLs visited provides a reasonable set of candidates for reuse u accounts for 43% of all Web pages visited u consider screen real estate, and cognitive overhead of scanning items u user able to predict if URL will be on the list

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #4 n Other strategies for presenting the history list, particularly pruning duplicates and hierarchical structuring, increase the probability of it containing the next URL u 26% of recurring total are not covered by last 10 items u more difficult to recall and/or locate these URLs

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #5 n History based on recency is not effective for all possible recalls because it lists only a few previous events; alternative strategies must be supported u a few URLs are frequently visited

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #6 n URLs already recalled through history should be easily reselectable u implicit: recency method u explicit: highlight item

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #7 n History items should have a meaningful representation u URLs versus titles u display length

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #8 n Support grouping of URLs into high-level Web tasks, and switching between tasks u context-sensitive Web subspaces u recency ordered hyperlink sublists

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Design Guideline #9 n Allow end-user customization of history data u customize attributes of history items u save portions of browsing history

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Conclusion n Empirical data u justifies need for browser history mechanisms u provides foundation for design guidelines n Current stack-based model can be improved upon

Design Guidelines for Effective WWW History MechanismsLinda Tauscher & Saul Greenberg Future research n Evaluate cognitive and physical effort of alternative history list methods n Access impact of different HTML and browser articfacts e.g. frames n Validate design principles