Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (61 page)

300 Glossary

Import
Data that implies that data is being received for use from another soft-
ware system or another user. With respect to CAD, neutral files are often Im-
ported to the CAD system. This would include files such as DXF, IGES, STEP,
VRML, etc. Obviously, the sending system Exports the data.

Instance
Refers to a somewhat intelligent copy of an aspect or feature of the
computer software or system. In a GUI different windows can be different in-
stances of the program (i.e. running the program two times at the same time). In a
2-D CAD system, the Groupings of entities can become multiple instances in the
drawing. In a 3-D CAD system, parts shown in an assembly model should be
considered instances of the parts. Instancing can imply that all the copies of the
item can be automatically changed by modifying a master copy of the item.
Interchangeability
The ability to use a new Revision of a part without concern
for the older Revisions. If a part is interchangeable, then either Revision of it can
be used without any problems. If a new Revision of a part is not interchangeable,
then it is often assigned a new Part Number. The handling of these situations are
referred to as Rules of Interchangeability.

Internet
A global system of computer networks. It was related to the Arpanet
(connected with the U.S. Defense Advanced Research Projects Agency
[DARPA]) which connected government, industry, and educational institutions.
Aspects of the Internet would include the World Wide Web, global e-mail, ftp
(File Transfer Protocol) sites (where files could be uploaded and downloaded),
and use-groups (an electronic bulletin board system based on topics). Many as-
pects of computer networking were developed in conjuction with the Internet (for
instance, IP).

Internet Address
See IP Address.

Intranet
An Internet-like or web-like approach to linking together computers
at an individual company or institution for use within the company or institution
only.

IP Address (Internet address)
A numerical address assigned to a computer on
a computer network. Unlike the Ethernet address (which is assigned to hard-
ware), the IP Address can be configured or assigned. It is a set of 4 numbers sep-
arated by a period. The range of the numbers in the different positions can
indicate a scheme of subnetworking; these schemes are referred to as Classes.
Item Master
Refers to a master list of all Part Numbers used by a company. It
forms a master database of much of a manufacturer’s current and past products.
These Part Numbers may be assigned to parts, assemblies, BOMs, specifications,
technical publications, material specifications, etc.

JAVA
A computer programming language that has many of the advantages of
C++, but it also is designed to assist with programming for the Internet. A basic
feature of JAVA is that GUI types of programs are made to work regardless of the
computer hardware and operating system (so called “interoperability”). It was de-
veloped by Sun Microsystems.

Glossary 301

JPEG
A type of image data file. It contains Bitmap data. It does not contain
Vector data; therefore, it is not appropriate for translation to a CAD system.
JPEG files are often used in conjunction with a web browser.

Join
A 3-D part creation operation where different sets of 3-D data are brought
together. Joining also can imply the determination of the intersection of surfaces
such that a new bounded volume is created (i.e. Joining determines how surfaces
must be stitched up). Join can be considered a Boolean operation for the 3-D
model.

Kernel
A feature of an operating system. In this case, the Kernel is like a mas-
ter program that always runs or is resident in Memory. The Kernel loads and con-
trols all the other program’s use of Memory. This approach tends to be stable
since the Kernel program can keep programs from corrupting each other’s use of
Memory. Second, a Kernel is a central or core set of programming in an applica-
tion program. For 3-D CAD systems, there are Kernels that CAD software ven-
dors can buy or license to provide the basic algorithms for making 3-D surfaces,
features, etc. If CAD systems standardize on the same Kernel, then these systems
will interoperate to some degree.

Key
Used in database programs to identify the most important fields of the
data. For instance, a database of all drawings in a CAD system could use the
Drawing or Part Number field as the Key. This means that the database can be
most easily sorted, searched, etc. using this field. If there is more than one Key,
then the Key with the highest precedence is called the Primary Key, the next one
is the Secondary Key, etc. Just because a Key is used, does not mean that the data
base can’t be searched or sorted based on another field, however.

Kinematics
Refers to the analysis of just the motion of parts in an assembly
model. Unlike Dynamics (which figures out motion based on forces and torques),
Kinematics assumes that some forcing function is applied somewhere to make
some part or parts move. Then the Kinematics are solved to figure out where all
the other parts move in relation to that applied forcing function.

LAN (Local Area Network)
Typical for creating a somewhat localized com-
puter network. At one time they would be limited to a single office or building.
Over time, the extent of LANs has increased. Different LANs are often connected
together via a backbone. Also, see WAN.

Layout
Refers to a high level of design work. At this stage of design, basic or
major components are placed in the context of the overall product design. Subse-
quently, more specific design is performed for all the components (known as de-
tailing). A drawing that shows the design at the layout level is referred to as a
Layout Drawing.

Leader
A line on a drawing that points from a note or other text-based entity to
an appropriate segment of geometry. It may have an arrowhead to assist with in-
dicating the proper geometry.

302 Glossary

Levels of Detail (LOD)
Indicates how much detail is generated for viewing a
3-D model from a certain distance (or zoom). This could apply to the appearance
of surface textures or the tessellations on the model. Usually, the Graphics
Adapter allows a 3-D model to be manipulated interactively; however, when the
model appears too crude (for instance, circular-type surfaces show up as coarse
polygons), then the CAD software must regenerate the data stored in the Graph-
ics Adapter. This creates a new Level of Detail. These Levels of Detail can be
remembered in the system to accelerate performance. They may also be stored in
the actual CAD files for later use.

Library
In computer programming, a set of routines or functions that can be
re-used (as in a DLL). In a CAD system, a Library would typically mean a logical
organization of CAD data files (as in “check drawings into a Library”).
Lighting
Refers to the light sources that a Graphics Adapter assumes to figure
out the Shading of a 3-D object. The position, intensity, “diffuseness,” color, etc.
of Lighting can change the appearance of the 3-D object.

Line
A geometric entity that follows the formula of a straight line; this formula
extends the line infinitely. However, in a CAD system or drawing it really refers
to a line segment (that is, some finite amount of the line). Line Work
refers to the
entities in the drawing that are supposed to be on the object being documented (as
opposed to notes, dimensions, etc.).

Line Weight
Refers to the thickness or heaviness of lines shown on a drawing.
A heavy line is thick and dark and is more obvious; a light line is thin and more
subtle. Lines that are supposed to be on the object being documented (such as
edges of the part) are to be heavy. Lines that are not really on the object (like
centerlines) are not.

Linux
A version of unix that is considered open source. This means that no one
company really owns or controls the program.

LOD
See Levels of Detail.

Loft
A 3-D part modeling operation that creates surfaces that try to follow and
blend among some cross sections. Usually these cross sections are somewhat dis-
similar (i.e. blending from a rectangular cross section to a circular cross section).
Machine Code
See Machine Instructions.

Machine Instructions
The most low-level commands that a computer system
uses. These instructions are specific codes that a particular CPU understands.
These instructions would include moving data from one address to another; or
adding one number to another number and storing the result in a register, etc. All
computer software on a system must eventually be turned into this basic set of
instructions. Only very rarely are programs written at this level.

Mainframe
A computer that is expected to control a large number of users.
Furthermore, the users are assumed to have little or no processing power. In this
scheme, there is really just one CPU and users compete for use of that CPU. In
the computer networking approach, very large computers that may also be file

Glossary 303

servers might be referred to as mainframes. However, the adoption of computer
networking (or client/server technology) pretty much negates the need for main-
frames (particularly for CAD).

Manifold
Refers to a part model that has all edges of all surfaces meeting just
one other surface’s edge. If more than two surface’s edges meet at the same loca-
tion, then a nonreal part or abstraction results. In a real part, the insides of sur-
faces must bound material, not other surfaces.

MDA
An acronym for Mechanical Design Automation. It has been used by
CAD system vendors to distinguish their more sophisticated systems, since the
acronym CAD can still be associated with just creating CAD drawings. However,
most users still refer to all these systems as CAD systems.

Memory
The volatile data medium used directly by a computer system. It can
also be thought of as just memory chips (ICs). It should not be confused with the
nonvolatile Storage system that can permanently store data (such as a Disk
Drive). There are a variety of types of Memory, such as RAM, ROM, DRAM,
etc., but in general referring to Memory of a computer system implies the main,
system, or core RAM or memory that the CPU uses with all its operations.
Mesh
A grid of geometric data that is created to assist with the calculations of a
CAE program. The Mesh may be 2-D or 3-D. It contains individual points (called
nodes) and regions that surround the points (called elements). The Mesh breaks
down designed parts or assemblies into many small regions.

Metadata
Data that gives information about other sources of data (i.e. “data
about data”). Probably the most common use of Metadata in a CAD system is
with databases that control and/or track the location of the operating system files
that represent CAD data (part, assembly, drawing, and BOM files).

Minicomputer
A computer that is larger than a microcomputer (i.e. a PC), but
it is smaller than mainframes. They were instrumental in the development of a
number of CAD systems in the 1980s; however, most CAD systems now use a
client/server architecture or just standalone PCs.

MIPS (Millions of Instructions Per Second)
A performance parameter for
computers that are not doing Floating Point Calculations (they are doing “inte-
ger” calculations). It gives an indication of the most basic performance of the
computer system. However, Floating Point Calculations are usually a much more
important performance characteristic for computers running CAD systems (so
MIPS can be ignored).