Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (54 page)

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11.2.6 User Management

The 3-D CAD database management should also consider the privileges of differ-
ent users or classes of users. In many organizations, there is a distinction between
users that can administrate the CAD database and those that work with it. For
instance, a company may want to limit the number of users that can delete certain
items or records in the CAD database. This typically is done with information
that is considered released or active. This information (models, drawings, BOMs,
etc.) is often critical for manufacturing or product support, and it may require
added security.

Controlling access to the critical information may entail security at more
than one level. First, users should be prevented from deleting the operating sys-
tem files (i.e. DWG, PRT, ASM, DBF files). This security is dependent on the
particular operating system being used, but usually folders or directories or in-
dividual files can be protected against delete privileges for users (except for the
administrator).

Beyond the operating system protection, the CAD database management
software can usually be used to restrict access to information, as well. In this
case, users may be working on different projects or within different departments,
and it may be desirable to make sure their data is not accidentally altered by the
wrong users. These different departments may be given their own libraries or
drawers within the context of the CAD database, and the CAD system may allow
an administrator to allow only certain users access to these various libraries. The
administrator should also protect the data organization itself so that users can not
inadvertently delete or alter the libraries, drawers, folders, etc. or other types of
customizations.

11.3 DATA MANAGEMENT

(THE USER PERSPECTIVE)

Having presented CAD data management from the administrator’s point of view,
this section presents CAD data management from the users point of view. Of
course, administrators should become familiar with this perspective, as well.

11.3.1 Ownership and Revision Control

Probably the most fundamental issue of data management from the designer’s
point of view is ownership and revision control. When all design work was based
on paper drawings, ownership of an aspect of product design was based on who
actually had a given paper drawing in their possession. Unlike computer files that
can be easily duplicated over and over again, duplicates of paper drawings would
generally be discouraged (at least for use by designers). Thus, it was fairly simple
to resolve ownership over an aspect of design. The designer with possession of a

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drawing would be able to make changes to the drawing as deemed necessary. But
with the 3-D CAD system, where so many items are tracked by the CAD data-
base software, and there is a web of interrelated parent/child relationships be-
tween the items, there are many more possible scenarios of ownership and users
need to become more savvy with understanding how the 3-D CAD data manage-
ment works.

The idea of a vault is helpful in understanding ownership of data. When
someone needed to work on a paper drawing, it was often taken from a vault or
print room. As with a library of books, this could be referred to as checking out a
drawing. As the drawing was removed from the vault a record was also made of
who took the drawing, when it was taken, etc. This paradigm is often carried over
into the 3-D CAD system. If someone needs control over a 3-D model, then they
would check it out from a virtual vault, cabinet, library, etc. Once this has been
done by a designer, this particular 3-D model would become off limits for other
designers to make changes. Just like a single book in a library, it can not be
checked out twice at the same time. This restricted access capability can be re-
ferred to as revision control (although items may be checked out for other reasons
besides an actual design revision to an item).

It is important to have this sort of data access scheme applied via database
management software with the 3-D CAD system. The non-metadata approach of
simply relying on the naming and locations of files in the operating system is not
very reliable with respect to revision control. Once a part file is copied or re-
named, there is no robust tracking of who did it, when they did it, where it was
copied to, etc. This operating system file manager approach should be avoided.

11.3.2 Assembly Revision Control

Checking out a 3-D part model to control the part’s design is relatively simple;
there is just one item to control. The designer checks out the part model in order
to change it. The CAD database software records this activity, and then no other
designers would be able to then check it out.

However, in many cases, there are 3-D assembly models which are the par-
ents of the 3-D part model (i.e. the BIKE_ASSY assembly model in the previous
chapter is the parent of the SEAT part model). Now, the checkout concept be-
comes more complicated. For instance, one designer could be responsible for the
assembly model, while another designer or designers would be responsible for
the parts. The assembly designer now will need to have copies of the part models,
but this designer will need to be prevented from actually changing the parts. On
the other hand, the designers changing the parts will probably not be able to de-
sign these parts without seeing the overall design context (i.e. the parent assem-
bly). Thus, the part designers need a copy of the assembly, but they must be

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prevented from changing the assembly model (for instance, moving parts around
within the assembly).

A common solution to the issues presented by assembly revision control is
the concept of reference. In paper drawing management systems, there was a
stamp that could be placed on drawings that said, “For Reference Only.” This
was stamped on a copy of a master drawing when a designer needed to see a
drawing from the vault, but he or she did not actually check out this drawing. The
designer could then see the state of the design at that moment, but there was no
real guarantee that it would remain current (since someone could go ahead and
check it out and change it later). In order to clearly show that the copy was not the
master drawing, “For Reference Only” was stamped on the drawing.

It is not difficult to transfer the concept of “For Reference Only” into the 3-
D CAD system. When a designer needs to see other 3-D models for designing
within the context of the overall project, copies are made of the other 3-D models
for the designer but the CAD database software records the fact that these copies
are “For Reference Only.” Using the example of a bicycle assembly again, the
designer that checks out the entire bicycle assembly could just reference the front
wheel assembly. In this case, it is assumed that this designer would be able to
change the position of the front wheel assembly within the context of the overall
assembly. But, this designer would not be able to actually change the front wheel
assembly or its constituent parts.

Although the “For Reference Only” approach is basically practical, it can
be rather complicated and difficult for some users to work with. For instance, us-
ers may try to check out parts without checking out the proper parent assembly or
understanding the “where used” issues. If a user checks out a part that is used by
an assembly, and that assembly is checked out by another user, there may be no
guarantee the changes to the part will be accepted in that assembly unless the
users cooperate in the design control.

This is just one example of the complicated nature of assembly data man-
agement that can result with multiple users working on the same design. There
are even more variables that can play into these scenarios such as configuration
management (where different options are available for a product), constraints
(where users may need to constrain assemblies together without owning all the
assembly models), assembly drawings (where one user may need to just add a
note to an assembly drawing, but not change the geometric characteristics of the
assembly model), etc. Although this is a complex matter, it is essential that users
eventually understand and work within the CAD database management system.
The problems (such as who really controls the design of the bicycle) are really
design control issues, not database software issues. The database software is
merely trying to keep all the data properly organized and controlled.

Of course, using “For Reference Only” is only one approach to the team-
based assembly design. Another approach would be to allow all the part design-

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ers and the assembly designer full access to all the models (even across the Inter-
net). In this case, each of the designers would be changing each others view of
the design context in real time. This approach may be manageable for conceptual
design and other prerelease design activities. But, once a design is released to
production, a more systematic approach of checkout and reference would proba-
bly be needed to demonstrate an appropriate level of design control (as required
by quality system and management systems such as ISO 9001).

11.3.3 Part Numbering and Revision Levels

Another important data management issue from the perspective of the user is
naming conventions. When items are created in the 3-D CAD system, they need
to be given consistent names by all users. This makes it much easier for users to
locate models and data. This is especially important since 3-D CAD systems con-
tain so many kinds of files and data.

The vast majority of companies use a part numbering system as the primary
tracking scheme for all their product data. The part number system may actually
use letters and numbers, but it is customary to call them part numbers anyway. In
this case, the part number could easily be used as the naming convention for the
parts, assemblies, BOMs, etc.

Obviously, the most important characteristic of the part numbering system
is that each item (part, assembly, specification, etc.) has a unique identifier. Often
there is a master part numbering software that provides these numbers. Many
companies will also use an intelligent part numbering system where certain kinds
of items will have different starting numbers. For instance, BOMs may start with
one particular number (such as “1.”), drawings with another number (such as
“2.”), specifications with another number (such as “3.”), and hardware (such as
nuts and bolts) with another number (such as “4.”), etc. Intelligent part number-
ing is very valuable with paper controlled processes, but with the use of database
management software in a 3-D CAD system, it can be of less importance. In this
case, items can be sorted and searched based on various keys irrespective of the
part number (such as whether it is a BOM, drawing, specification, or hardware).

If users have to locate their parts and assemblies by file name alone (which
again is not a recommended approach), then obviously the best solution is to use
the part number as the file name. Of course, operating system file naming con-
ventions must then be followed. This may restrict the type of characters that can
be used, and it may limit the length of the file names (and thus the part number-
ing). The part numbering system used in conjunction with a 3-D CAD system
would also preferably not use nonalphanumeric information. In other words, only
numbers and letters are used. Characters such as hyphens (-), slashes(/ or \),

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pound signs (#), etc. should be avoided. Almost all of these characters are re-
served for special meanings for the operating system.

In addition to using part numbers, virtually all manufacturers use the con-
cept of revision level to indicate the proper version or revision of a design and its
constituents. This is extremely important as most designs are produced in an iter-
ative process. The most common schemes for indicating revision levels is to use
numbers or letters. A part model at revision “0,” could be considered the initial
release. The first revision would be a “1,” the second revision would be a “2,” etc.
Companies may also use letters. In this case, perhaps no letter would be the initial
release, and then A would be the first revision. Unfortunately, database software
may not allow a blank for the revision field, and thus some other character will
need to indicate the initial release.