Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (59 page)

Dialog Box
In the GUI environment, a form or small window that appears from
the computer program. It is usually a presentation of information to the user, or it
is a means for entering new data into the computer program.

Dimension
A type of constraint that fixes the distance between two geometric
elements. On a drawing, dimensions can be indicated between points and/or
lines. However, in a drawing, dimensions do not drive or constrain the 2-D geom-
etry. Instead it is just a measurement of the distance between the elements. If the
number shown in the dimension is changed, the shape of the geometry in the
drawing would not change. In a 3-D model, dimensions are usually constraints
and they can drive changes to the drawn geometry. Dimensions in an assembly
model would drive changes between entire parts.

Directory
A logical partitioning of a Storage system (such as a Disk Drive).
Different directories usually contain different types of files. A program file di-
rectory would contain files for programs loaded on the computer system, for
instance.

Disk Drive
A Storage system that can store and more or less permanently save
the data. They use a spinning disk and tiny regions of magnetism to record the
information. A Disk Drive may also be referred to as a hard drive, C drive, hard
disk. This is to distinguish it from a Diskette Drive.

Diskette
A portable medium for exchanging data files between computers. It is
inserted into a Diskette Drive (or floppy drive), data is written on it, and then it is
removed. They can also be referred to as floppies.

DLL (Dynamic Link Library)
A type of file that works in conjunction with a
computer program that does not load all its instructions into the Memory system
when the program starts. Instead, pieces of instructions are loaded and executed

Glossary 293

on a more as needed basis. DLLs are also often shared between totally different
programs (which may be part of the operating system or written by users).
DOS
The de facto operating system for the PC platform prior to the use of
GUIs on PCs. It was the primary product from Microsoft Corporation that was
instrumental in the standardization of PCs. It operated in a character or command
processor mode where commands were typed into the system using the keyboard.
It has been replaced by the Windows operating system and its derivatives. There
was also a DOS (Disk Operating System) that was used by mainframe comput-
ers, but this is rarely what is meant by DOS.

DOS Prompt
The means for entering commands to the DOS operating system.
It has come to mean entering commands into any computer system directly (as
opposed to interacting with the GUI).

Download
The retrieving of data files from a remote source. This could mean
obtaining a copy of a file from a file server, mainframe, or from the Internet.
Drawing Number
A field in the Title Block of a drawing. It indicates the
unique number assigned to that drawing, and usually by inference to the object
documented in the drawing. In many cases, the Drawing Number would be the
Part Number, as well.

Drawing Package
A set of drawings that are managed as a group. Typically
they are used during drawing release, and the list of drawings in the package usu-
ally share a release number of some kind (for future reference). Drawing Pack-
ages may also be used in exchanging a set of information between groups or
companies.

Drawing Size
An indicator of the overall size of a hard copy of a drawing. In
the inch system, they are letters such as A, B, C. In the mm system, they are the
letter A followed by a number (e.g., A1, A2, A3, etc.). ASME (ANSI) and ISO
standards specify the standard sizes. It is included in the Title Block of drawings.
Driver
A small amount of programming in a file that enables a device or sys-
tem to communicate with a larger system. For example, a plotter expects a certain
set of codes to create drawings. The CAD software may not produce these codes
directly, but rather rely on a Driver to do the transformation. Drivers are generally
employed to make a program less dependent on specific computer hardware.
DXF
A CAD drawing neutral file format. It allows a CAD drawing (generally
presumed to be 2-D) to be exchanged or translated between two different CAD
systems. It was developed by the company that produces AutoCAD. It has been
adopted by many other CAD system vendors.

Dynamics
Refers to the analysis of mechanisms or assembly models where the
forces and torques on the system are applied, evaluated, and/or predicted. A Dy-
namics simulation can predict how an assembly model will behave based on an
actual physical environment. Although this capability may appear in a CAD sys-
tem, it is really a CAE function. Dynamics is different than Kinematics; Kine-

294 Glossary

matics is where parts of an assembly model move, based on some driving motion
(instead of forces).

E-CAD
A generic term for CAD-type systems for electronics design. Although
E-CAD may be used to lay out the physical arrangements of components on a
PCB (Printed Circuit Board), most of the effort in E-CAD is concentrated on the
interconnection and simulation of the components (i.e. the schematic).
ECN
Engineering Change Notice or Engineering Change Number. See Release.
ECR
Engineering Change Record or Engineering Change Release. See Release.
ECO
Engineering Change Order. See Release.

ERP (Enterprise Resource Planning System)
A system of software that is
supposed to manage many aspects of a manufacturer’s operations (i.e. enterprise-
wide). These systems are usually considered an expansion on MRP (Material Re-
source Planning) software. Of particular interest is that the ERP system may be
responsible for the Bills of Material that are relevant to the Parts Lists or BOMs
shown on drawings or in 3-D assembly models.

Ethernet
Ethernet is a basic computer networking technology based on the
“collision–retry” technique. It can really be thought of as broadcasting through a
wire. Computers on the network listen for their data and react accordingly. If the
transmission is interrupted; it simply tries again.

Ethernet Address
Uniquely identifies a computer on a network at the hard-
ware level. These addresses are assigned to each individual Network Interface
Card (NIC) or ethernet card. The NIC is the circuit board and componentry that
implements the networking capability. An Ethernet Address is a sequence of 8
bytes (shown in a form such as xx:xx:xx:xx:xx:xx).

Export (of data)
Implies that data is being prepared for use by another soft-
ware system or another user. With respect to CAD, neutral files are often Ex-
ported from the CAD system. This would include files such as DXF, IGES,
STEP, VRML, etc. Obviously, the receiving system Imports the data.
FCS (Feature Control Symbol)
It is a set of graphical symbols, letters, and
numerical values that indicate special geometric requirements associated with di-
mensions. For example, an FCS on a drawing next to a dimension for a hole in a
plate may indicate that the axis of the hole must be perpendicular to the face of
the plate within a number of degrees.

FEA (Finite Element Analysis)
CAE software that is used to predict the be-
havior of designs. It is most often used for stress analysis. Stress analysis calcu-
lates the stresses in models; stress is a mathematical representation of how the
loads (forces) may deform an object. FEA computer programs can also solve
other kinds of problems. FEA programs work with a Mesh. A Mesh is a model
that is broken down into a large number of small regions where the actual mathe-
matics is applied. CAD data (2-D or 3-D) is often used as the starting point for
these Finite Element Models. Some CAD systems will have a direct connection
between CAD and FEA; others will use neutral files (such as IGES Surfaces).

Glossary 295

Feature
A segment or region of a part. For example, a hole, rib, or boss on a
part would be referred to as a feature. With respect to 3-D part modeling, an oper-
ation to create one of these regions is obviously referred to as a feature. However,
a 3-D part modeling technique can create many holes at one time. Now, the 3-D
CAD system may refer to a feature of the part meaning a single operation (or a
step in a part history), when in fact many geometric features are created at the
same time.

Features-based Modeling
The overall method of 3-D part modeling where the
part model is built in a series of steps (captured in a part history), and each step
begins by sketching 2-D geometry on an existing plane on the part model.
File Extension
A means of quickly identifying a type of computer file by the
end of the file name. For some operating systems, they are of a fixed format
and/or length. For others, they are at the discretion of the programmer or user.
Most operating systems recognize the File Extension based on the presence of a
period or dot; however, GUIs often just portray the File Extension as a column in
a table of file names. Some File Extensions are de facto standards; others are not
standardized at all. For example, a file ending with the letter C (e.g. FIXIT.C)
would be universally recognized as a file with C programming source coe. How-
ever, a file ending in DAT (e.g. FIXIT.DAT) could be any number of data files for
many purposes.

File Format
Indicates the basic structure of the data in a file. The most impor-
tant distinction for File Formats are ASCII versus Binary. In a FORTAN pro-
gram, a formatted file that is created by the program is basically an ASCII file,
and an unformatted file is basically a Binary file. Therefore, sometimes a file may
be referred to as formatted versus unformatted (but this really means ASCII ver-
sus Binary).

File Server
A computer on a network that is primarily acting as a source of
files for other computers. It allows files to be stored and managed centrally.
File System
A distinct set of files that are part of an overall directory structure
for a computer. File Systems generally allow multiple Disk Drives to appear to a
user as a single system. For example, in a unix system, all files under a directory
/usr may use one Disk Drive (or a partition of the drive), while all files under a
directory /home may use another Disk Drive (or a partition of the drive). In this
example, the /usr and /home File Systems are then mounted to the root directory
(or /). If this mount point is actually implemented across a network to another
computer, this is referred to as a Network File System.

Fillet (pronounced “fill-it”)
A type of feature on a part that rounds a corner or
blends surfaces meeting at an angle. Virtually all physical parts have fillets when
surfaces meet; it is basically impossible to create a perfectly sharp corner in a
physical part. Sometimes the fillets are specifically modeled or dimensioned in a
drawing. In other cases, notes are used to indicate that all corners are filleted to
some standard amount.

296 Glossary

Filter
In a CAD system refers to limiting the appearance of certains types of
entities, attributes, or database items. For example, to filter for dimensions in a
drawing means to have the CAD system select all the dimensions (so that they
can all be changed in some way). Another example, would be to filter by color. In
this case, the CAD system would select or operate on all the surfaces in a 3-D
model that are a certain color. If one is searching for a specific Part Number in
the CAD system data base, then to more easily identify a match, the filter may
indicate that specific Part Number.