Ajax Design and Usability

Transcription

1 Ajax Design and Usability William Hudson Ajax Design and Usability About Ajax Ajax in context How Ajax works How Ajax is different How Ajax is similar Computer-Human Interaction Change blindness Attentional gambling Flow Feedback Design and usability guidelines Copyright 2006 Syntagm Ltd 2 1

2 Activity 1 Agree/elect/appoint a spokesperson/note taker Discuss the issues raised on the worksheets At the end of the discussion the spokesperson will give a verbal summary (3 5 minutes) to the whole group Copyright 2006 Syntagm Ltd 3 Activity 1 Worksheet issues 1. Introductions name, company, job role 2. What does Ajax mean to you? 3. Describe some of your most pressing user experience problems. Do you think Ajax will help? 4. Do feel any pressure to use AJAX? What form does it take? Copyright 2006 Syntagm Ltd 4 2

3 Mandatory Image Copyright 2006 Syntagm Ltd 5 Optional Image Copyright 2006 Syntagm Ltd 6 3

4 Ajax in Context AJAX Asynchronous JavaScript And XML Copyright 2006 Syntagm Ltd 7 Ajax in Context AJAX Asynchronous JavaScript And XML not needed client and server can use any convenient data format Copyright 2006 Syntagm Ltd 8 4

5 Ajax in Context AJ Asynchronous JavaScript not really, it could be any scripting language such as VBScript Copyright 2006 Syntagm Ltd 9 Ajax in Context A Asynchronous only relative to page loading, to users it looks synchronous Copyright 2006 Syntagm Ltd 10 5

6 Ajax in Context So what is Ajax? Copyright 2006 Syntagm Ltd 11 Ajax in Context Ajax Remote Scripting It s an approach for making server requests without reloading a page Relies on non-standard server request facilities (XMLHttpRequests for example) supported by most browsers Uses Document Object Model (DOM) scripting to make changes to the current page, for example: Show popup windows (div elements) Change the contents of page elements Hide, delete or move page elements Copyright 2006 Syntagm Ltd 12 6

7 Ajax Example: Google Maps Google Maps allows near-real-time scrolling and zooming Copyright 2006 Syntagm Ltd 13 How Ajax Works Get Page HTTP Page Returned (Eventually) A standard page request without scripting Copyright 2006 Syntagm Ltd 14 7

8 How Ajax Works Script... Event Handler HTTP request Data Returned An asynchronous request within a page Copyright 2006 Syntagm Ltd 15 How Ajax is Different Without Ajax (in general) Request is for a URL Anything that is returned must be a complete page with appropriate headers With Ajax Client-side scripts use non-standard XMLHttpRequest to make a request for data The data does not have to be XML! Request can complete at any time but user is not left waiting for a new page Updates achieved through the Document Object Model Copyright 2006 Syntagm Ltd 16 8

9 Technical Benefits of Ajax Unit of information reduced from a complete page (or frame) can be as little as a single character Faster than returning a whole page Data-oriented requests means greater code reuse especially server-side (in form validation, for example) Overall approach can be much more like a desktop application A major benefit of Ajax is reduced granularity a Copyright 2006 Syntagm Ltd 17 Ajax Example: Google Suggest 1) Just the a is sent to the server 2) Only the visible list is returned (but in no obvious order) Copyright 2006 Syntagm Ltd 18 9

10 Technical Drawbacks of Ajax The asynchronous data requests rely on technology that is not standard (yet) Different code needed on different browsers Requests may not complete in a timely fashion (or at all) Pages laden with code will take longer to load Network overheads may make short transfers slow in proportion Copyright 2006 Syntagm Ltd 19 How Ajax is Similar Installation Speedy Start Granularity Portability Maintenance Sophistication HTML Only ***** **** * ***** ***** * Simple Client-Side Scripting ***** *** * ***** **** ** DOM Scripting (with iframes) ***** *** *** **** *** *** Flash *** ** *** *** *** **** Java Applets ** * ***** *** ** **** AJAX ***** ** ***** **** ** **** Desktop Applications * ***** ***** * * ***** More asterisks are better! Copyright 2006 Syntagm Ltd 20 10

11 How Ajax is Similar Installation Plug-in or installation required (*=full installation) Speedy Start How quickly users can start to interact (*=long wait) Granularity The smallest unit of data updates (*=page) Portability Portability across platforms (*=none) Maintenance Difficulty of making and distributing changes (*=very) Sophistication Richness of the user experience (*=limited) Copyright 2006 Syntagm Ltd 21 Ajax User Experience User experience of Ajax can be better than the traditional page-at-a-time model (but not necessarily) We need to consider some Computer-Human Interaction (CHI) issues first: Change blindness Attentional gambling Flow Feedback Copyright 2006 Syntagm Ltd 22 11

12 CHI Change Blindness Change blindness means that we cannot easily see the differences between two images when they are separated by a blank field (Diagram courtesy of Ron Rensink) Copyright 2006 Syntagm Ltd 23 CHI Change Blindness Can you spot the difference in the two scenes? Copyright 2006 Syntagm Ltd 24 12

13 CHI Change Blindness Color and large top margin used to draw attention to changes Copyright 2006 Syntagm Ltd 25 CHI Change Blindness Only 44% of observers noticed the gorilla while counting the number of ball passes between teams. The gorilla was on screen for 5 seconds! The paper (called Gorillas in our midst ) won an IgNoble prize in See Copyright 2006 Syntagm Ltd 26 13

14 CHI Change Blindness Copyright 2006 Syntagm Ltd 27 CHI Attentional Gambling Having performed an action, users must gamble on where to look next Users complete the form and then look here Unfortunately they need to look here Copyright 2006 Syntagm Ltd 28 14

15 CHI Attentional Gambling Usually, having clicked in a left-navigation panel, users will focus their attention on the content area Users gamble on looking at A but lose since B is where they needed to look Copyright 2006 Syntagm Ltd 29 CHI Visual Perception Summary Change blindness changes will not be noticed, especially if A page reload is involved Users are distracted Attentional gambling users will not attend to content or navigation If it isn t where they expected it to be If they are distracted Appropriate use of popups and animation can assist both problems but beware of Distracting users and Flow Copyright 2006 Syntagm Ltd 30 15

16 CHI Flow Mihaly Csikszentmihalyi s theory of flow describes optimal psychological experience Living in the moment Lack of distraction (for CHI a transparent interface ) Appropriate pacing of activity Appropriate degree of difficulty Coupled with flow, we need to make sure that users feel Their effort is rewarded They are getting closer to their goal (information foraging theory) Copyright 2006 Syntagm Ltd 31 CHI The Flow Curve Adapted from Kathy Sierra s Featuritis Curve Copyright 2006 Syntagm Ltd 32 16

17 CHI Feedback Feedback needs to be close to its cause in three aspects: Time Space Meaning The time and space aspects are also related to attentional gambling (when and where users are expecting to look) Copyright 2006 Syntagm Ltd 33 Activity 2 Agree/elect/appoint a different spokesperson/note taker Discuss the issues raised on the worksheets and supplied handouts At the end of the discussion the spokesperson will give a verbal summary of the discussions (3 5 minutes) to the whole group Copyright 2006 Syntagm Ltd 34 17

18 Activity 2 Worksheet issues: Discuss the good and bad points of Ajax relative to 1. Change blindness 2. Attentional gambling 3. Flow 4. Feedback (See the separate handout for a reminder of these topics) Copyright 2006 Syntagm Ltd 35 Ajax and Change Blindness Biggest contributor to change blindness is reloading the page Ajax can fix this, but there is also: Attentional gambling (are users looking in the right place?) and splash blindness to contend with Copyright 2006 Syntagm Ltd 36 18

19 Splash Blindness See Change blindness as a result of mudsplashes in Nature, March 1999 Copyright 2006 Syntagm Ltd 37 Ajax and Attentional Gambling Updating pages without reloading is only effective if users are looking in the right place or the change attracts attention by being large, colourful or animated Copyright 2006 Syntagm Ltd 38 19

20 Ajax and Attentional Gambling Change is here But users are looking here When nothing appears to happen, users focus on the progress bar the update at the top of the page would be invisible, even with Ajax Copyright 2006 Syntagm Ltd 39 Ajax and Attentional Gambling Order line shows popup detail when moused-over, but users still need to notice that it s there Copyright 2006 Syntagm Ltd 40 20

21 Ajax and Flow Of course, Ajax (or just DOM scripting) would let you do something like this: Copyright 2006 Syntagm Ltd 41 Ajax and Flow But flow requires an optimum amount of feedback: More Feedback Better Copyright 2006 Syntagm Ltd 42 21

22 Ajax and Feedback For server-based validation Ajax can provide much more timely feedback than the page-at-a-time model However, timely client-side validation requires only DOM scripting Copyright 2006 Syntagm Ltd 43 Ajax and Feedback Confusingly, this whole page was reloaded when the delivery method changed, just so the delivery cost could be updated Copyright 2006 Syntagm Ltd 44 22

23 Design and Usability Guidelines 1. Do not focus on the technology: Use Ajax to address usability and user experience problems with the page-ata-time model. Copyright 2006 Syntagm Ltd 45 Design and Usability Guidelines Ajax used to spice up the user experience On the same page changing quantity has no effect Priority should have been given to fixing the serious usability problem caused by requiring a page update instead a popup was added Copyright 2006 Syntagm Ltd 46 23

24 Design and Usability Guidelines Updating an expired credit cards takes forever on most web sites on Amazon.co.uk it takes two clicks but with no Ajax in sight Copyright 2006 Syntagm Ltd 47 Design and Usability Guidelines 2. Do not be over-optimistic about update speeds. The recommendation for thinclient computing is a minimum of 100 MB/S (about 100 times better than many broadband connections) Consider Ajax only for moderate volumes of code and data Copyright 2006 Syntagm Ltd 48 24

25 Design and Usability Guidelines Google Maps is no Google Earth this image eventually took a full minute to load at 512 KB/S Copyright 2006 Syntagm Ltd 49 Design and Usability Guidelines 3. Help users to gamble with their attention effectively make updates: visually obvious or where users attention will be focussed Copyright 2006 Syntagm Ltd 50 25

26 Design and Usability Guidelines A temporary popup in the vicinity of the Add button is a safe bet Copyright 2006 Syntagm Ltd 51 Design and Usability Guidelines 4. Do not cause more problems than you solve with Ajax: Make sure the browser back button still works Deal with delayed or missing server responses by implementing timers Optimize flow by avoiding excessive feedback, especially message boxes that have to be dismissed by users Copyright 2006 Syntagm Ltd 52 26

27 Design and Usability Guidelines 5. Remember that most users do not really care about the technology Copyright 2006 Syntagm Ltd 53 Design and Usability Guidelines Microsoft s Outlook Web Access is a spectacular example of Ajax technology but most ordinary users wonder why it isn t more like the desktop version Copyright 2006 Syntagm Ltd 54 27

28 Questions? Copyright 2006 Syntagm Ltd 55 28