Information Technology Reference
In-Depth Information
Along with the notion of work is the requirement for control. If what
is to be pushed is event dependent (e.g., a file is to be created or a Web
page to be formed), then using push allows one to wait for that event to
occur, or complete, before triggering the push event. Push also allows
control over scheduled events.
Push also appears to allow more efficient creation and broadcast. The
file or data is made ready once and sent to everybody, perhaps in a
broadcast mode. The normal issues with broadcasts and availability come
into play — for example, how to handle the situation if the receiver is
not ready. The data sent out is as of the time that the pusher scheduled
its creation; this may or may not be acceptable to the receiver. Push can
appear simple but has a tendency to become complex.
Push does not mean being pushy. Permissions may be required, such
as in proper e-mail marketing. One may have to set up subscriptions or
memberships. Push can interrupt something, while pull appears more
polite. In many situations, taking an interruption approach is more effi-
cient. Phone rings interrupt us and tell us that someone is calling us. If
the occurrence of an event is less frequent than its nonoccurrence,
interruption is more efficient. One designs the system to handle or store
less frequently occurring, or fewer, values or states. This is somewhat
similar to the data modeling strategy when faced with choices whether
to keep a table of positives or negatives: should the table record employees
who are enrolled (for an event) or those who are not enrolled?
The control point for pull is more with the party doing the pulling,
which requests data at a time of its choice. This data may be ready to be
pulled or may have to be put together at the time of request, possibly
because the requests are random or customer specific or parameter-driven
values must be supplied before anything can be done. Each creates a
different kind of load on the systems. The demand pattern on certain
resources may become variable, although not totally unpredictable. There
may be patterns to business or human behavior patterns driving such
requests — people coming to the office at approximately the same time,
month-end statements, and others, making them somewhat predictable
even in on-demand situations.
Pull does not imply total freedom of choice. One can pull only from
what is offered, such as in a restaurant menu.
Sometimes there is a third party doing the controlling, asking someone
to do the push or someone else to do the pull. Sometimes the process
is partially push and partially pull. A certain amount of processing is
completed and pushed to an intermediate point, ready for subsequent
pull. Maybe there is some notification involved in the completion of push
or the readiness for pull.
