LabVIEW is a general-purpose programming system, but it also includes
libraries of functions and development tools designed specifically for data
acquisition and instrument control. LabVIEW programs are called virtual
instruments (VIs) because their appearance and operation can imitate actual
instruments. However, VIs are similar to the functions of conventional
language programs.
A VI consists of an interactive user interface, a dataflow diagram that
serves as the source code, and icon connections that allow the VI to be
called from higher level VIs. More specifically, VIs are structured as
follows:
• The interactive user interface of a VI is called the front panel,
because it simulates the panel of a physical instrument. The front
panel can contain knobs, push buttons, graphs, and other controls
and indicators. You enter data using a mouse and keyboard, and
then view the results on the computer screen.
• The VI receives instructions from a block diagram, which you
construct in G. The block diagram is a pictorial solution to a
programming problem. The block diagram is also the source code
for the VI.
• VIs are hierarchical and modular. You can use them as top-level
programs, or as subprograms within other programs. A VI within
another VI is called a subVI. The icon and connector of a VI work
like a graphical parameter list so that other VIs can pass data to a
subVI.
With these features, LabVIEW promotes and adheres to the concept of
modular programming. You divide an application into a series of tasks,
which you can divide again until a complicated application becomes a
series of simple subtasks. You build a VI to accomplish each subtask and
then combine those VIs on another block diagram to accomplish the larger
task. Finally, your top-level VI contains a collection of subVIs that
represent application functions.
Because you can execute each subVI by itself, apart from the rest of the
application, debugging is much easier. Furthermore, many low-level
subVIs often perform tasks common to several applications, so that you can
develop a specialized set of subVIs well-suited to applications you are
likely to construct.
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