Information Technology Reference
In-Depth Information
connection between the source and destination. At the same time, most
people, when asked what
online
is, will probably say that means
inter-
active
.
Real-time in common usage often refers to the outside real-world time.
Real-time means to process data as it is generated. This is the concept
used in the real-time virus scan of a computer system — the anti-virus
program is constantly scanning all inputs to the system for potential threats,
as they come in. This must be done in a way such that users cannot sense
a slowdown. The fact is that there is nothing such as “true” real-time. The
advantage of real-time in such situations is that the threat is discovered
at the earliest.
Real-Time versus Batch
Real-time updates to a database, as compared to batch updates, signify
that the inserts, updates, or deletes are taking effect immediately instead
of at a later time. Transactional systems are said to operate in real-time.
This is an expectation that is related to the online, interactive nature of
systems. If one enters a purchase order and hits “Submit,” one expects it
to have been recorded in the system and be available to others at that
same instant. If there is batch processing of such information, then it is
not likely available immediately. This may not be obvious to all users.
There are some important considerations when deciding to build real-
time systems. Is the data entered all the time or intermittently? Furthermore,
who is the consumer of the data and in what frequency? Batch systems
have been found to be better in terms of spreading bulk work from high-
demand periods to low-demand periods (banks do bookkeeping at night
when the number of customer transactions decrease). One advantage with
batch systems is that one can do a simple rollback if the data does not
appear consistent. However, the downside is that time delays inherent in
batch processing mean that one's systems reflect an earlier state of what
is happening in one's business. It is as if one is driving by looking at the
rear-view mirror.
Note that batch processes can be run at various frequencies. For
example, if the Purchase Order database was being updated in a batch
mode every 15 minutes, then the real time of this batch system is 15
minutes.
There are many situations where the real time should not be instan-
taneous. This is a design choice and introduces what is called an “error
gap.” An example is a self-service account creation program. New account
information is saved and reviewed by a person before being allowed to
update the Account database. Automation of this error gap could be done
through formal workflow systems. By retaining a manual error gap in the
