Glossary of LabVIEW terms

This is a glossary of LabVIEW terminology.

A

absolute path

File or directory path that describes the location relative to the top level of the file system.

active cell

Cell of a listbox, table, digital data, or tree control to which you can apply property changes.

active window

Window that is currently set to accept user input, usually the frontmost window. The title bar of an active window is highlighted. Make a window active by clicking it or by selecting it from the Windows menu.

ancestor class

Any LabVIEW class that is the parent, grandparent, and so on, of another LabVIEW class. The LabVIEW Object may be the ultimate ancestor.

application

Application created using the LabVIEW Development System and executed in the LabVIEW Run-Time System environment.

application instance

Instance of LabVIEW created for each target you create in a LabVIEW project. When you open a VI from the Project Explorer window, the VI opens in the application instance for the target. There is a separate instance of LabVIEW running for each target you create. LabVIEW also creates a main application instance, which contains open VIs that are not part of a project and VIs that you did not open from a project. See also target.

Application Programming Interface (API)

Programming interface for controlling software packages.

application zone

Memory allocation section that holds all data in a VI except execution data.

array

Ordered, indexed list of data elements of the same type.

array shell

Front panel object that houses an array. An array shell consists of an index display, a data object window, and an optional label. It can accept various data types.

artificial data dependency

Condition in a dataflow programming language in which the arrival of data, rather than its value, triggers execution of a node.

asynchronous execution

Mode in which multiple processes share processor time. For example, one process executes while others wait for interrupts during device I/O or while waiting for a clock tick.

Auto-indexing

Capability of loop structures to disassemble and assemble arrays at their borders. As an array enters a loop with auto-indexing enabled, the loop automatically disassembles it extracting scalars from 1D arrays, 1D arrays extracted from 2D arrays, and so on. Loops assemble data values into arrays as data values exit the loop in the reverse order.

autoscaling

Ability of scales to adjust to the range of plotted values. On graph scales, autoscaling determines maximum and minimum scale values.

autosizing

Automatic resizing of labels to accommodate text you enter.

B

bit array tag

Multibit value representation of a connection to a real-world I/O point or memory variable. In LabVIEW, this type of tag can be comprised of up to 32 discrete values.

BNF

Backus-Naur Form. A common representation for language grammars in computer science.

Boolean controls and indicators

Front panel objects to manipulate and display Boolean (TRUE or FALSE) data.

Block diagram

Pictorial description or representation of a program or algorithm. The block diagram consists of executable icons called nodes and wires that carry data between the nodes. The block diagram is the source code for the VI. The block diagram resides in the block diagram window of the VI.

breakpoint

Pause in execution used for debugging.

Breakpoint tool

Tool to set a breakpoint on a VI, node, or wire.

broken arrow

See broken Run button below.

broken Run button

Button that replaces the Run button when a VI cannot run because of errors.

broken VI

VI that cannot run because of errors; signified by a broken arrow in the broken Run button.

buffer

Temporary storage for acquired or generated data.

Bundle function

Function that creates clusters from various types of elements.

byte stream file

File that stores data as a sequence of ASCII characters or bytes.

C

C string (CStr)

A series of zero or more unsigned characters, terminated by a zero, used in the C programming language.

caption label

Label on a front panel object used to name the object in the user interface. You can translate this label to other languages without affecting the block diagram source code. See also Name Label.

case

One subdiagram of a Case structure.

Case structure

Conditional branching control structure that executes one of its subdiagrams based on the input to the Case structure. It is the combination of the IF, THEN, ELSE, and CASE statements in control flow languages.

cast

To change the type descriptor of a data element without altering the memory image of the data.

chart

2D display of one or more plots in which the display retains a history of previous data, up to a maximum that you define. The chart receives the data and updates the display point by point or array by array, retaining a certain number of past points in a buffer for display purposes.

See also: scope chart, strip chart, and sweep chart.

checkbox

Small square box in a dialog box you can select or clear. Checkboxes generally are associated with multiple options that you can set. You can select more than one checkbox.

child class

A LabVIEW class that inherits data and member VIs from an ancestor LabVIEW class.

CIN

Code Interface Node (CIN). Special block diagram node through which you can link text-based code to a VI.

CIN source code

Original, uncompiled text code.

See also: object code and Code Interface Node (CIN).

class

A category containing properties, methods, and events. Classes are arranged in a hierarchy with each class inheriting the properties and methods associated with the class in the preceding level.

class library

The group of VIs that define a LabVIEW class. The class library also stores the data of the LabVIEW class.

cloning

To make a copy of a control or another object by clicking it while pressing the <Ctrl> key and dragging the copy to its new location.

Cluster

A set of ordered, unindexed data elements of any data type, including numeric, Boolean, string, array, or cluster. The elements must be all controls or all indicators.

cluster shell

Front panel object that contains the elements of a cluster.

code resource

Resource containing executable machine code. You link code resources to LabVIEW through a CIN.

coercion

Automatic conversion LabVIEW performs to change the numeric representation of a data element.

coercion dot

Appears on a block diagram node to alert you that you have wired data of two different numeric data types together. Also appears when you wire any data type to a variant data type, or when LabVIEW discards bits of a fixed-point number.

Coloring tool

Tool to set foreground and background colors.

compile

Process that converts high-level code to machine-executable code. LabVIEW compiles VIs automatically before they run for the first time after you create or edit alteration.

concatenated Pascal string (CPStr)

A list of Pascal-type strings concatenated into a single block of memory.

conditional terminal

Terminal of a While Loop that contains a Boolean value that determines if the VI performs another iteration. A conditional terminal also can be added to a For Loop to stop execution early when a condition occurs.

connector

Part of the VI or function node that contains input and output terminals. Data values pass to and from the node through a connector.

connector pane

Region in the upper right corner of a front panel or block diagram window that displays the VI terminal pattern. It defines the inputs and outputs you can wire to a VI.

constant

A terminal on the block diagram that supplies fixed data values to the block diagram.

See also: universal constant and user-defined constant.

content rectangle

Region of a listbox, table, digital data, or tree control that contains all headers and cells. The content rectangle does not include scroll bars.

Context Help window

Window that displays basic information about LabVIEW objects when you move the cursor over each object. Objects with context help information include VIs, functions, constants, structures, palettes, properties, methods, events, dialog box components, and items in the [Project Explorer] window.

continuous run

Execution mode in which a VI runs repeatedly until the operator stops it. Click the Continuous Run button to run a VI repeatedly.

Continuous Run button

Icon that indicates a VI is set to execute repeatedly until the user stops it.

contour plot

Plot where contour lines are used to connect points of equal value.

control

Front panel object for entering data to a VI interactively or to a subVI programmatically, such as a knob, push button, or dial.

control flow

Programming system in which the sequential order of instructions determines execution order. Most text-based programming languages are control flow languages.

Controls palette

Palette that contains front panel controls, indicators, and decorative objects.

conversion

Changing the type of a data element.

UTC

Coordinated Universal Time. Time scale that is determined using highly precise atomic clocks. LabVIEW uses UTC as the standard for the internal representation of dates and times.

count terminal

Terminal of a For Loop whose value determines the number of times the For Loop executes its subdiagram.

current VI

VI whose front panel, block diagram, or Icon Editor is the active window.

D

data dependency

Condition in a dataflow programming language in which a node cannot execute until it receives data from another node.

See also: artificial data dependency

Data flow

Programming system involving the creation of block diagrams having executable nodes connected by wires, where the wires between nodes indicate that data produced by one node is used by another node. Nodes may execute when they have received all necessary input data and may produce output data to other nodes in the diagram. G is a dataflow system.

data storage formats

Arrangement and representation of data stored in memory.

data type

Format for information. In LabVIEW, acceptable data types for most VIs and functions are numeric, array, string, Boolean, path, refnum, enumerated type, waveform, and cluster.

data type descriptor

Code that identifies data types; used in data storage and representation.

datalog file

File that stores data as a sequence of records of a single, arbitrary data type that you specify when you create the file. Although all the records in a datalog file must be a single type, that type can be complex. For example, you can specify that each record is a cluster that contains a string, a number, and an array.

default

Preset value. Many VI inputs use a default value if you do not specify a value.

default input

Default value of a front panel control.

deploy

To download items or apply settings to a target in the Project Explorer window.

descendant class

A child, grandchild, and so on, of another LabVIEW class.

dialog box

Window that appears when an application needs further information to carry out a command.

dimension

Size and structure of an array.

directory

Structure for organizing files into convenient groups. A directory is like an address that shows the location of files. A directory can contain files or subdirectories of files.

DLL

Dynamic Link Library

drag

To use the cursor on the screen to select, move, copy, or delete objects.

drive

Letter in the range a-z followed by a colon ":", to indicate a logical disk drive.

driver

Software that controls a specific hardware device, such as a DAQ device.

DTbl

Digital table.

DWDT

Digital waveform data type.

dynamic data type

Data type used by Express VIs that includes the data associated with a signal and attributes that provide information about the signal, such as the name of the signal or the date and time the data was acquired. Attributes specify how the signal appears on a graph or chart.

dynamic dispatch

A VI that defines a method of a LabVIEW class. Dynamic dispatch member VIs are VIs with the same name that occur throughout the class hierarchy. Similar to polymorphic VIs, LabVIEW determines at run time which member VI to call.

E

edit mode

When you can make changes to a VI.

empty array

Array that has zero elements but has a defined data type. For example, an array that has a numeric control in its data display window but has no defined values for any element is an empty numeric array.

encapsulation

The consolidation of data and methods into a LabVIEW class, where the data is accessible only through class member VIs.

end of file (EOF)

Character offset of the end of file relative to the beginning of the file. The EOF is the size of the file.

Error cluster

Consists of a Boolean status indicator, a numeric code indicator, and a string source indicator.

error in

Error cluster that enters a VI.

Error List window

Window that displays errors and warnings occurring in a VI and in some cases recommends how to correct the errors.

error message

Indication of a software or hardware malfunction or of an unacceptable data entry attempt.

error out

The error cluster that leaves a VI.

Event Data Node

Node attached to the left and right sides of an Event structure indicating the available data for the event you configured that case to handle. If you configure a single case to handle multiple events, only the data that is common to all handled event types is available.

event driven programming

Method of programming whereby the program waits on an event to occur before executing one or more functions.

execution highlighting

Debugging technique that animates VI execution to illustrate the data flow in the VI.

Express VI

A subVI designed to aid in common measurement tasks. You configure an Express VI using a configuration dialog box.

F

FIFO

First-in-first-out memory buffer. The first data stored is the first data sent to the acceptor.

file refnum

Reference number. An identifier that LabVIEW uses as reference to a file object. Use a file refnum as an input parameter for certain file IO functions.

filter events

Allow control over how the user interface behaves.

Flat Sequence structure

Program control structure that executes its subdiagrams in numeric order. Use this structure to force nodes that are not data dependent to execute in the order you want if flow-through parameters are not available. The Flat Sequence structure displays all the frames at once and executes the frames from left to right until the last frame executes.

flattened data

Data of any type that has been converted to a string, usually for writing the data to a file.

For Loop

Iterative loop structure that executes its subdiagram a set number of times with the option of stopping execution early when a condition occurs. Equivalent to text-based code: For i = 0 to n — 1, do...

Formula node

Node that executes equations you enter as text. Especially useful for lengthy equations too cumbersome to build in block diagram form.

frame

Subdiagram of a Flat or Stacked Sequence structure.

free label

Label on the front panel or block diagram that does not belong to any other object.

front panel

Interactive user interface of a VI. Front panel appearance imitates physical instruments, such as oscilloscopes and multimeters.

function

Built-in execution element, comparable to an operator, function, or statement in a text-based programming language.

Functions palette

Palette that contains VIs, functions, block diagram structures, and constants.

G

G

Graphical programming language LabVIEW uses.

I

Icon editor

Interface similar to that of a graphics program for creating VI icons.

L

LabVIEW

Laboratory Virtual Instrument Engineering Workbench. LabVIEW is a graphical programming language that uses icons instead of lines of text to create programs.

N

NaN

Digital display value for a floating-point representation of <Not A Number>. Typically the result of an undefined operation, such as log(–1).

O

Operating tool

Tool to enter data into controls or to operate them.

P

polymorphism

Ability of a node to automatically adjust to data of different representation, type, or structure.

R

race condition

Occurs when two or more pieces of code that execute in parallel change the value of the same shared resource, typically a global or local variable.

S

sequence local

Terminal to pass data between the frames of a Stacked Sequence structure.

T

terminal

Object or region on a node through which data values pass.

V

virtual instrument (VI)

Program in LabVIEW that models the appearance and function of a physical instrument.

W

Wiring tool

Tool to define data paths between terminals.