# IBM Visualization Data Explorer Programmer's Reference

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# Chapter 18. Glossary

This glossary defines important abbreviations and terms. It includes information from IBM Dictionary of Computing (ZC20-1699).

A
Array | An ordered list of data items of the same type represented by an Array Object. Arrays are either irregular or compact. See also compact Array, irregular Array.
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
cache | The cache service provides various parts of the system with a means to store the results of computations for later reuse. Each cache entry is uniquely identified by a string function name, an integer key (used by the executive to store multiple outputs for a single module), the number of input parameters, and the set of input parameter values.
camera | A camera defines the position and orientation of the viewer, the volume of interest of the object being viewed, and the size of the image to contain the resulting view.
canvas | The large open area of the VPE window that is used to build and edit visual programs.
clipping plane | A plane that divides a 3-dimensional volume into a region that is rendered and a region that is not rendered. This allows the inside of an object to be seen.

compact array

Any one of five varieties of compact encoding of array data. The varieties are:

- regular
- path
- product
- mesh
- compact.

component | A basic part or classification of a Field; each component is indexed by a string and its value is an Object. 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 group of Fields that together is treated a single Field. This type of Field is useful, for example, for certain kinds of simulation data that are represented by disjoint grids. A Composite Field is a collection of compatible Fields, all having a "positions" component of the same dimensionality, "data" components of the same type, and "connections" with the same "element type." It is required that members be disjoint and abutting.

connections | A component of a Field, specifying how data points in that Field are joined together.
constant Array | An Array with a constant value.
contour | Lines on a surface that connect points with the same data value.
D
dependent | A description of a component attribute. One component is said to be dependent on another if the items in the component arrays are in one-to-one correspondence with each other.
E
executive | The component of the Data Explorer system that manages the execution of modules specified using the scripting language. This term is often used to refer to the entire server portion of the Data Explorer client-server model, including the executive, modules, and data management components.
export | To write an Object to a specified Data Explorer-format external data file. For example, importing an ASCII file can be slow. You can export the data in a binary format for faster access. You can also import data, operate on it, and then export the transformed data for future use.
F

Field

A self-contained collection of information necessary to represent scientific data. A Data Explorer Field typically is made up of a series of components and other information as required. It includes the data itself in the form of a "data" component, a set of sample points in the form of a "positions" component, optionally, a set of interpolation elements in the form of a "connections" component, and other information as needed.

filter | A program that converts data to a Data Explorer format.
flat shading | A shading model in which each polygon of an object is shaded using a single intensity value. Contrast with Gouraud shading.
fork-join parallelism | A programming concept that allows 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
glyph | A figure that is mapped to a particular variable. The length, angle, or other attribute of the figure relates to the value of the particular 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.
Group | A collection of Objects.
grow | Add information from neighboring partitions to a Composite Field. Generally necessary only in a parallel environment.
H
handle | A data structure that is a temporary local identifier for an Object.
hash table | A table of Objects that is accessed with a search key (the hash value).
hidden | A module input parameter that does not appear by default in the module configuration dialog box. Hidden parameters are typically those less commonly used in visual programs.
I
Image window | IBM Data Explorer window that displays the image generated by a visual program.
import | To read in an external data file.
interactor | A Data Explorer device used to manipulate data in order to change the visual image produced by a program. See also interactor stand-in.

interactor stand-in

An icon used in the visual program editor window to represent an interactor. Stand-ins are named after the type of data they accept. The five types are:

- integer
- scalar
- string
- selector
- value.

interpolation element | An interpolation element provides a means to interpolate between a specified set of sample points. The set of interpolation elements for a particular Field constitutes the "connections" component.
invalid positions and connections | Marked positions and connections that are ignored by modules.
irregular Array | An Array Object in which the data is stored explicitly, as opposed to a compact Array.
isosurface | A surface in 3-dimensional space that connects points with the same data value.
item | A single piece of data in an Array Object.
J
join | An operation that merges two or more computation paths.
L
light | An Object that illuminates a scene.
M
macro | In IBM Data Explorer, a sequence of modules that are be collected together. A macro cannot have recursion at any level.
makefile | A file used by the UNIX** utility "make" that contains a list of source files and commands required for maintaining current versions of Data Explorer programs. The modification times of the files determine what files have changed since the last time "make" was run, and therefore, what commands must be executed.
mdf | See module description file.
member | An individual unit in a group. A collection of members makes a group.
mesh Array | A compact Array that encodes multidimensional regularity of connections. It is a product of connection Arrays. The product is a set of interpolation elements in which the product has one element for each pair of elements in the two multiplicands, and the number of sample points in each element is the product of the number of sample points in each of the multiplicands' elements.
module | A primitive function that is provided as part of IBM Data Explorer, such as the Isosurface module. The same term is used for the function's icon, which is its visible representation in the VPE window.
Module Builder | A graphical user interface to assist in the creation of user-defined modules.

module description file (mdf)

A module description file is used by a programmer who is adding a module to Data Explorer to describe information about the module that is needed by the system.

A module description file contains the name of the module, a short description of it, a category for the user interface to put the module in, and the names and descriptions of the input and output parameters. The module description file is used by the executive and the user interface to name parameters. The module description file is also used by the graphical user interface to form a tool icon in the proper category with the right number of input and output tabs.

MultiGrid

A MultiGrid Group is another kind of Group that is treated as a single entity. Like a Composite Field, all of the members of a MultiGrid Group must have the same type of data and the same type of connections. It is not required that members be disjoint and abutting however. Overlapping grids can be used along with the "invalid positions" and "invalid connections" components to define which grid is valid in a particular region.

N
netCDF | See Network Common Data Form.
Network Common Data Form (netCDF) | A data abstraction that stores and retrieves scientific data structures in self-describing, multiple dimensional blocks. netCDF is accessible with C or FORTRAN. netCDF is not a database management system.
O
Object | A region of global memory that contains an identification of its type plus additional type-dependent information.
P
parallelism | The concurrent execution of modules.
partition | A member of a Composite Field.
partitioned Field | A Composite Field.
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.
pick | One Object that was picked using the mouse.
pick path | A list of integers that describe how to traverse an Object's hierarchy to reach a particular picked object.
pick structure | A Field that identifies objects picked using the mouse. It contains the components "positions," "pick paths," "picks," and "pokes."
poke | One screen location that was poked, or selected, by the user. One poke may result in none, one, or more than one pick.
positions | A component of a Field, consisting of a set of points.
private Object | Objects containing arbitrarily stored data. These Objects can be stored in the cache for later use.
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.
pseudo key | Accesses Objects in a hash table.
R
realization | The representation of data in terms of boundaries, surfaces, transparency, color, and other graphical, image, and geometric characteristics.
regular Array | A compact Array that is a set of n points lying on a line with constant spacing between them, representing 1-dimensional regular positions.
rendering | The generation of an image from some representation of an object. Rendering can be done from a surface representation, or from volumetric information.
ribbon | Ribbons are derived from lines (e.g., streamlines and streaklines). Ribbons may twist to indicate vorticity.
S
scripting language | The IBM Data Explorer command-line language. The scripting language is available for users who choose to write visual programs in a programming language. Data Explorer uses the scripting language to manage the execution of modules and to invoke visualization functions.

Series

A Series is intended to represent a single Field sampled across some parameter, such as time or temperature (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.

Every member of the Series must have the same dimensionality, say n, the same data type, and the same connections element type. Members are stored in and retrieved from a Series Group by index rather than by name. Members cannot be retrieved by Series value.

shading | Applying lights to a surface during the rendering process.
shrink | Generally necessary only in a parallel environment; deletes the information, previously added by Grow, from neighboring partitions of a Composite Field. Composite Field members are returned to their original size.
stand-in | See interactor stand-in.
streaklines | Lines, sometimes called rakes, that show the path of particles over time.
string Object | A character string stored in an Object.
T
tiling | Combining shaded surface and volume interpolation elements to produce an image.
tool | A general term used to describe any of the icons used by IBM Data Explorer to build a visual program, specifically modules, macros, or interactor stand-ins.
tube | Tubes are derived from lines (e.g., streamlines and streaklines). Tubes may twist to indicate vorticity.
V
value | (1) A specific occurrence of an attribute (e.g. for the attribute "color"). (2) A quantity assigned to a constant, a variable, a parameter, or a symbol.
visual program | A user-specified interconnection of Data Explorer modules that performs a sequence of operations on data.
Visual Program Editor | Data Explorer graphical user interface for creating and editing visual programs and macros. See also canvas.
VPE | See Visual Program Editor.
volume | An object that fills a 3-dimensional space. A solid ball is a volume. A surface, however, is infinitely thin and does not fill space even though it exists in three dimensions.
volume rendering | A technique for creating an image that shows not just the surface of a 3-dimensional object, but its contents as well. The interior details being visualized may be physical, such as bone and muscle in a human body or the structure of a machine part, or they may be other characteristics such as fluid flow, heat, or stress.

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