## Chapter 3. Glossary

Some of the definitions in this glossary are taken from the IBM Dictionary of Computing, SC20-1699.

A
array | In Data Explorer, an array structure containing an ordered list of data items of the same type along with additional descriptive information. Arrays are either compact or irregular. See compact array, irregular array.
assembly | An object representing a collection of objects.
attribute | A characteristic of an object. Objects can have attributes that are indexed by a string name and have a value that is an object. See also component attribute.
C
cell-centered data | Connection-dependent data.
clipping plane | A plane that divides a three-dimensional object into a rendered and an unrendered region, making the object's interior visible.
colormap | A map that relates colors to data values. The colors are carried in the map's "data" component and the data values to which each color applies in its "positions" component.
colormap editor | A special tool for mapping precise colors to specified data values, the results of which are displayed in a visual image.

compact array

Any of five types of compact encoding of array data:

  constant array
  mesh array
  path array
  product array
  regular array

component | A basic part of a field (such as "positions," "data," or "colors"); each component is indexed by a string (e.g., "positions"), and its value is typically an array object (e.g., the list of position values). See also component attribute.
component attribute | A characteristic of a component. Components of a field can have attributes that are indexed by a string name and have a value that is an object.
composite field | A grouping of like fields for processing a single spatial entity. See also partitioned field.
connection | Component of an IBM Data Explorer data field that specifies how a set of points are joined together. Also controls interpolation.
connection-dependent data | Cell-centered data. The data value is interpreted as constant throughout the connection element.
contour | On a surface, a line that connects points having the same data value (e.g., pressure, depth, temperature).
cube | A volumetric connection element that connects eight positions in a data field.
cutting plane | An arbitrary plane, in three-dimensional space, onto which data are mapped.
D
data-driven interactors | Interactors whose attributes (such as minimum and maximum) are set by an input data field.
Data Prompter | An interface that enables a user to describe the format of the data in a file. The prompter creates a General Array Format header file that is used by the Import module to import the data.
dependence | A component attribute. One component is said to be dependent ("dep") on another if the items in their component arrays are in one-to-one correspondence to each other.
E
element | Connection item.
element type | An attribute that describes the type of connection element, for example, "cubes", "tetrahedra", or "lines".
executive | The component of the Data Explorer system that manages the execution of specified modules. The term often refers to the entire server portion of the Data Explorer client-server model, including the executive, modules, and data-management components.
F
face | (1) Any planar surface that bounds a three-dimensional object. (2) A polygon.
field | A self-contained collection of data items. A Data Explorer field typically consists of the data itself (the "data" component), a set of sample points (the "positions" component), a set of interpolation elements (the "connections" component), and other information as needed.
flat shading | A shading model in which each face of an object is shaded with a single intensity value. Contrast with Gouraud shading.
fork | An operation that causes a program to branch into two or more parallel concurrent paths.
fork-join parallelism | A programming mechanism that supports parallel processing: The fork statement splits a single computation into multiple independent computations. The join statement recombines two or more concurrent computations into one.
G
general array format | A data-importing method that uses a header file to describe the data format of a data file. This "format" makes it possible to import data in a variety of formats.
glyph | A graphical figure used to represent values of a particular variable. The length, angle, or other attribute of the glyph is some function of the value of that variable. Each occurrence of a glyph represents a single value of the variable.
Gouraud shading | Also called intensity interpolation shading. A shading model in which the intensity of values of incident illumination on a polygon are interpolated from intensity values at the vertices of the polygon. Contrast with flat shading.
I
icon | A displayed symbol that a user can point to with a device such as a mouse to select a particular operation or software application.
image window | IBM Data Explorer window that displays the image generated by a visual program. Associated with the Image window are special interactors for 3-D viewing.
interactor | A Data Explorer device used to manipulate data in order to change the visual image produced by a program. See also data-driven interactor, interactor stand-in.

interactor stand-in

An icon used in the VPE window to represent an interactor. Stand-ins are named after the type of data they generate:

- integer
- scalar
- selector (outputs a value and a string)
- string
- value
- vector

interpolation element | An item in the connections component array. Each interpolation element provides a means for interpolating data values at locations other than the specified set of sample points. See positions component.
invalid | A classification of an array item (typically positions or connections). An invalid item is not to be rendered or realized.
irregular array | In contrast to a compact array, an array in which the data is stored explicitly.
isosurface | A surface in three-dimensional space that connects all the points in a data set that have the same value.
isovalue | The single value that characterizes each and every point constituting an isosurface. By default, this value is the average of all the data values in the set being visualized.
J
join | An operation that merges two or more computation paths.
L
line | An element that connects two positions in a field.
M
macro | In IBM Data Explorer, a sequence of modules that acts as a functional unit and is displayed as a single icon. Macros can also be defined in the Data Explorer scripting language.
member | An individual unit or object in a group. A collection of members makes a group.
menu bar | In windows, a horizontal bar that displays the names of one or more menus (or tasks). When the user selects a menu, a pull-down list of options for that menu is displayed.
mesh array | A compact array that encodes multidimensional regularity of connections. It is a product of path arrays. In a mesh array, which positions are connected to one another is implicitly rather than explicitly defined.
N
navigate | To move the camera (changing the "to" and "from" points) around the image scene, using the mouse.
netCDF | Network Common Data Form.
network | In Data Explorer the set of tool modules, interactor stand-ins, and connections that constitute a visual program. In the VPE window, a network appears as a set of icons connected by arcs.
Network Common Data Form (netCDF) | A data format that stores and retrieves scientific data in self-describing, multidimensional blocks (netCDF is not a database management system, however). netCDF is accessible with C and FORTRAN.
normal | (1) Perpendicular to a surface. (2) In IBM Data Explorer, a vector that is perpendicular to a face or surface of an object. A normal may depend on connections or positions. A connection-dependent normal results in flat shading; a position-dependent normal results in Gouraud shading.
O
object | In IBM Data Explorer, any discrete and identifiable entity; specifically, a region of global memory that contains its own type-identification and other type-specific information.
opacity | The capacity of matter to prevent the transmission of light. For a surface, an opacity of 1 means that it is completely opaque; an opacity of 0, that it is completely transparent. For volume, opacity is defined as the amount of attenuation (of light) per unit distance.
P
partitioned field | A composite field, created by partitioning a single field into a collection of separate fields; used for parallel processing and data-management purposes.
path array | A compact array that encodes linear regularity of connections. It is a set of n-1 line segments, where the ith line segment joins points i and i + 1.
polygon | (1) Any multi-sided planar figure. (2) A face of a three-dimensional object.
position-dependent data | Data that are in one-to-one correspondence with positions.
positions component | A component that consists of a set of dimensional points in a field.
probe | A list of one or more vectors that represent points in a graphical image. Probes can be used with Data Explorer tools that accept vectors as input (such as ClipPlane and Streamline) or to control the view of an image.
product array | A compact array that encodes multidimensional positional regularity. It is the set of points obtained by summing one point from each of the terms in all possible combinations. In the simplest case, each term is a regular array.
Q
quad | An element that connects four positions in a field.
R
realization | A description of how raw data is to be represented in terms of boundaries, surfaces, transparency, color, and other graphical, image, and geometric characteristics.
reference | A component attribute. One component is said to refer to another ("ref") if the items in the first array are integer indices into the second array. The connections component references the positions component.
regular array | A compact array that is a set of n points lying on a line, with constant spacing between them, which can represent one-dimensional regular positions.
rendering | The generation of an image from some representation of an object, such as a surface, or from volumetric information.
ribbon | A figure derived from lines (e.g., from streamlines and streaklines). Ribbons may twist to indicate vorticity.
S
sample point | A point that represents user data. Data is interpolated between sample points by interpolation elements (connections).
scalar | A non-vector value characterized by a single, real number.
scatter data | A collection of sample points without connections.
screen | An illuminated display surface (e.g., the display surface of a CRT or plasma panel).
scripting language | The IBM Data Explorer command language. Used for writing visual programs, to manage the execution of modules, and to invoke visualization functions.
sequencer | An IBM Data Explorer tool for creating "animated" sequences of images.
series | In IBM Data Explorer, used to represent a single field sampled across some parameter (e.g., a simulation of a CMOS device across a temperature range). Members of a series have a position. A copy of the position is found in the "series position" attribute.
shared | A term used to indicate the availability of a resource for use by more than one program at the same time.
specular reflection | A reflection from a shiny object.
stand-in | See interactor stand-in.
streaklines | Lines that represent the path of particles in a changing vector field. Also called rakes.
streamlines | Lines that represent the path of particles in a vector field at a particular time. Also called flow lines.
T
tetrahedron | A volumetric connection element that connects four positions in a field.
tool | In IBM Data Explorer, a general term for any icon used to build a visual program (specifically, module, macro, or interactor stand-in).
triangle | A connection element that connects three points in a field.
tube | A surface centered on a deriving line (e.g., a streamline or streakline). Tubes may twist to indicate vorticity. See also user display station.
V
value | An instance of an attribute (for example, "blue" as the value of the attribute "color").
vector | A quantity characterized by more than one component.
visual program | A user-specified interconnected set of Data Explorer modules that performs a sequence of operations on data and typically produces an image as output.
vertex | One of the positions that define a connection element.
volume | The amount of three-dimensional space occupied by an object or substance (measured in cubic units). To be distinguished from an object's surface, which is a mathematical abstraction.
volume rendering | A technique for using color and opacity to visualize all the data in a 3-dimensional data set. The internal details visualized may be physical (such as the structure of a machine part) or they may be other characteristics (such as fluid flow, temperature, or stress).
vorticity | Mathematically defined as the curl of a velocity field. A particle in a velocity field with nonzero vorticity will rotate.
W
wireframe | Connected lines that represent a surface.

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