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4.2 Social mechanisms in communication and collaboration 121

Other coordinating mechanisms that are employed by groups working together
are rules and conventions. These can be formal or informal. Formal rules, like the
compulsory attendance of seminars, writing monthly reports, and filling in of
timesheets, enable organizations to maintain order and keep track of what its mem-
bers are doing. Conventions, like keeping quiet in a library or removing meal trays
after finishing eating in a cafeteria, are a form of courtesy to others.

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Shared external representations
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Shared external representations are commonly used to coordinate people. We
have already mentioned one example, that of shared calendars that appear on
user's monitors as graphical charts, email reminders, and dialog boxes. Other
kinds that are commonly used include forms, checklists, and tables. These are pre-
sented on public noticeboards or as part of other shared spaces. They can also be
attached to documents and folders. They function by providing external informa-
tion of who is working on what, when, where, when a piece of work is supposed to
be finished, and who it goes to next. For example, a shared table of who has com-
pleted the checking of files for a design project (see Figure 4.8), provides the nec-
essary information from which other members of the group can at a glance update
their model of the current progress of that project. Importantly, such external rep-
resentations can be readily updated by annotating. If a project is going to take
longer than planned, this can be indicated on a chart or table by extending the line
representing it, allowing others to see the change when they pass by and glance up
at the whiteboard.
Shared externalizations allow people to make various inferences about the
changes or delays with respect to their effect on their current activities. Accordingly,

Figure 4.8 An external representation used to coordinate collaborative work in the form of
a print-out table showing who has completed the checking of files and who is down to do
what.