Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (35 page)

There are a few typical strategies for this organization. One strategy is to
use the operating system’s file management alone. Obviously operating systems
are not written to assist CAD management, so this is often not the best choice.
Another strategy is to use a database and database programming. This database
would be populated with various metadata for drawings (drawing or part num-
bers, revision levels, etc.). At that point, users can intelligently search, sort, re-
trieve, and revise the drawings. If the database and database programming is
implemented within the CAD system itself, then this whole approach can be in-
visible to the user. This also means that the CAD user could be insulated entirely
from the operating system. This could also mean that a mixed or heterogeneous
set of platforms (unix workstations and PCs) could be used in the same CAD
system at the same time.

6.3.1 Drawing Metadata

An important concept with respect to CAD data management is metadata. This is
a computer systems term that means “data about data”; this term is used by this
work a number of times to help explain data management. In the context of the
CAD system, this is information in a computer file (such as a database) that is
relevant to the overall organization of the many drawing files.

As an example, it has been mentioned already that drawing hardcopies can
be placed into vaults. In an actual vault, there were flat file cabinets where the
drawings were laid onto large horizontal drawers. These cabinets were based on
standard drawing sizes (as discussed in Section 4.4). The C-size drawings, for
instance, would be in a C drawer; D-size drawings would be in the D-size drawer,
etc.. A catalog of all the drawings in the vault might have entries such as
D081462 or E0604062.

The size letter would be an example of something relevant to the “meta-
data” for those paper drawings. It is a tag or “attribute” that would be needed
along with the drawing or part number in order to actually find the drawing in the
vault. One needed to know which set of drawers to look in to find a particular
drawing, so the drawing size letter is important in that file management system.
Other examples of information that would be relevant to drawing management

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would be the ECR number, revision level, the person that approved the drawing,
and the title of the drawing.

Although metadata can be created and used in a non-CAD drawing envi-
ronment, it is certainly easier to create, track, and utilize in the computer-based
system.

6.3.2 Database-Driven CAD Management

When CAD systems were first implemented, the CAD system probably had no
drastic impact on the vaulting and release process. The CAD system merely
generated the hardcopy that was placed into the vault. However, the computer
that runs a CAD system is quite capable of creating and maintaining the catalog
of drawings, so naturally the cataloging function should eventually be taken over
by a computer system. Something like a catalog is usually called a database for
any type of computerized system. A database uses and maintains many fields or
specially designated chunks of information that can be sorted, searched, and
printed, etc.

With a CAD database managing the drawing data, it becomes possible to
have the CAD system use and maintain many more tags or attributes for the draw-
ings by using the metadata items as the database fields. Now, users can obtain
valuable information such as reports that list and sort drawings by part number,
ECR number, date of release, etc. Users can also rely on the CAD database to help
find drawings and research the various impacts of a change to a drawing. As CAD
systems become more complex (particularly having to handle 3-D models), meta-
data as database fields becomes a necessity for managing the very large amounts
of data. Therefore, this capability should be used whenever possible.

A good database-driven system allows users to use standard database func-
tionality such as relational data base linking, record-locking, purging, etc. This
system should also allow CAD administrator to setup a scheme for organizing the
drawings according to designer and management needs. For instance, drawings
may be stored in a system of virtual vaults, cabinets, libraries, or group/user
based on an important field such as drawing number. Or, drawings may be stored
in the virtual cabinets based on product type or design team. Obviously, if these
cabinets are arranged and sorted by drawing number, then it will be easy to locate
a specific drawing by drawing number alone. If the cabinets are arranged and
sorted by product line, then it will be easy to locate a specific product item alone.
Hopefully, the choice of part number or product line for cabinets will not be a
large problem, however. The database manager software should allow the user to
search by product line despite the primary key or field being by drawing number,
and vice versa.

Although one of the fields in the database would probably be the operating
system file name, it is not necessary to have that field shown to the user. In this

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case, the user may be indicating a drawing title or drawing number to a field that
makes sense to them, while the CAD system itself would then automatically as-
sign a file name for the operating system. Now the operating system level can no
longer be of concern to the user. In terms of retrieval, the user can simply tell the
CAD system what the drawing or part number is, what the revision level is, etc.,
and the CAD system can then file the name accordingly. Furthermore, this allows
files to be stored in different directories, folders, file systems, or network file
servers even though the drawings all may appear to the user to be in the same
cabinet or library. This allows the system management functions to be independ-
ent of the CAD data management.

Building on the database driven CAD data management scheme, a CAD
system may also offer the capability to add a layer of security on top of the auto-
mated file management. In this case, not only does the CAD database manager
software control the finer details of how the data is stored, it may be used to re-
strict and grant access to the drawings at different stages of the development pro-
cess. This type of CAD system would keep track of the legitimate users for the
entire system, and then a CAD administrator could determine which of these us-
ers would be able to see, mark up, revise, and/or delete drawings. The need for
this level of security is not necessarily driven by a need to stop malicious users
(such as hacking). Instead, this level of security simply allows a complex process
(such as product design) to be managed effectively. It is not unusual for two dif-
ferent designers working on two different design projects to find themselves con-
flicting with each other. They may need to revise the same drawing at the same
time (since common parts may be shared across products for manufacturing effi-
ciency). A good security system in the CAD database will make sure that only
one user will gain revision control of the drawing at a time. While one user is
granted access to modify the drawing, other users would be locked out.

This layer of security also allows different types of users to be granted dif-
ferent privileges as a group. Perhaps only designers can revise drawings, only
managers can mark up drawings, and only CAD administrators can delete draw-
ings. This database driven CAD management can make sure that is what actually
happens.

Going beyond the definition of the different classes of users, a CAD system
may also be able to keep track of the stages of a project. So, when a drawing is
intended only as a concept or a preliminary layout (and not to drive actual manu-
facturing of a component or assembly), the CAD system may be able to make
sure that drawings are not allowed to be revised by anyone or released to manu-
facturing. Then, when the drawing is released and available for revisions, then the
CAD system can allow this to occur. This highest level of data management may
be referred to as PDM (Product Data Management); it may be part of a separate
computer software system called a PDM system.

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The larger the company or enterprise, or the more complex the final prod-
uct, the more important it is to manage the drawings as flawlessly as possible.
Poor business and even life-threatening situations for the public at large can re-
sult if the wrong drawing is used at the wrong time. Just one change in a note on
a drawing that indicates a stronger material to be used to make a single part can
be disastrous. Drawings must be well-organized and controlled through all revi-
sions for the life cycle of the product. A CAD system with a good database sys-
tem will make this task much easier.

6.3.3 File-Driven CAD Management

Having extolled the benefits of the database manager approach to the CAD sys-
tem, some companies may still rely on a pure file management strategy. In this
case, it is left to the CAD administrator and users to make use of the files and
folders provided by the operating system. This is really not data management, but
just file management. In this case, it is up to the users to maintain and organize
the drawings in a somewhat manual process. Users are being relied upon to name
the files correctly, put them in the correct directories, and probably delete them
when they are no longer needed.

The drawing must be identified by the file name alone. If someone needs to
find a specific drawing they will have to be able to identify the proper folder
needed (folders based on drawing number or product line, no doubt), or they will
be forced to search all the available directories based on a file name matching
method of some kind. Of course, if folders are based on drawing number, there is
no way to look in folders based on product line instead, and vice versa. Without
the CAD data base and the metadata fields, one will not be able to search for
drawings based on attributes such as who created the drawing, when it was re-
leased, the ECR number, revision level, and so on. One can only search based on
the file name, and the file name is going to have a very limited amount of infor-
mation within it. Obvious choices for inclusion in the file name would be draw-
ing number (assuming no characters that violate operating system conventions
are used in the company’s drawing number system), revision level, sheet number,
and the title from the Title Block.

Another problem with simple file management is revision control. As men-
tioned earlier, often there are conflicting needs for drawing revision (with more
than one user needing control of the drawing at the same time). In order to con-
trol which user actually has the control over revisions using just file management,
schemes such as moving CAD data files between different kinds of folders have
to be used. However, this file management is not automatic, and the scheme is
unlikely to be able to consider the stage of the product development process (i.e.
prototype versus existing product) or the state of the drawing (i.e. new drawing
versus revision).

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It may be quite difficult to prevent intentional or accidental deletion of files
in the file management approach. Practically by definition, users will have direct
access to the operating system and files (since they will be copying, moving, re-
naming files, etc.). If users are able to have read/write access to the directories or
folders (so that they can be revised or moved), then these users are often going to
get delete privileges as well. One solution to this problem may be to have CAD
administrator users that have the privilege to move the drawings between folders;
they would then be responsible for the file management on behalf of the general
population of users. However, this is clearly a function that can be automated
with the database management system, and if the database approach is used, then
this would allow CAD users to spend more time on design functions and less
time on administrative tasks.