What's the difference between Item Revision State and Item Lifecycle Phase?
PDXpert PLM software supports various data revision
approaches, including traditional pre-production numeric and production
alphabetic formats. Nonetheless, this topic explains why these traditional approaches should
be considered obsolete. We describe how using
only one revision format (alphabetic or numeric), coupled with PDXpert
software's built-in item lifecycle phase attribute, provides fine-grained control over product life cycle business rules while
reducing the cost and risk of managing item revisions. We believe that using a
single revision format regardless of the item's lifecycle phase is current best practice.
Item records, whether for document or part, must have one or more
revisions. An item revision represents the technical content at a specific
point in time; a released revision represents an item's
approved technical content at a point in time.
Separately, items have a lifecycle: they're conceived, designed,
prototyped, validated, produced, serviced, disposed of, and (when no longer
commercially viable) declared obsolete.
In PDXpert PLM software, an item's revision release
state and the item's lifecycle phase are independent attributes. Multiple
item revisions may share a common lifecycle phase, and a particular item
revision can move through several lifecycle phases.
Document and part revision states
Revision states reflect the availability, or "readiness for use", of a specific item
revision. PDXpert PLM software defines exactly 3 release states for any item revision:
- Pending (unreleased, pre-release, created, originated, etc.)
- Released (issued, authorized for use, active, in-use, etc.)
- Canceled¹ (superseded, obsolete, invalidated, void, removed
from use, inactive, etc.)
At any point in time, each item in PDXpert software may have no
more than one Pending revision and no more than one Released revision, and
zero or more Canceled revisions.
These business rules are applied regardless of the product data management
process used:
- Users can
discard an item revision in Pending state without effect or penalty.
- Users can use the revision in Released state according to the appropriate item
lifecycle business rules.
- Users may not
use a revision in Canceled state, and the revision must be retained to provide a
historical reference.
Note that the only state
that's relevant for production purposes is the Released state. And there are some corollary rules:
- Each released or canceled item revision must have an associated
implementing change (typically called an "engineering change notice" or
"engineering change order"). A pending revision need not be
associated with a change.
- For an item structure ("bill of materials"):
- A child component's pending revision may only appear on an
assembly's pending revision. An unreleased child revision can never be
used on a released or canceled parent assembly revision.
- Released items can appear as child components on a released parent
assembly revision, as well as on pending and canceled revisions of
parent assemblies.
- A canceled item revision may only appear on a canceled parent revision.
The three release states represent the simple life cycle of a specific item
record revision, but do not say anything about what business rules apply to the item
while the revision is in its released state.
Document and part lifecycle phases
The item lifecycle phase identifies a set of company-specific business rules
that are used as the item moves from conception through to production, and is
finally retired.
Any number of item lifecycle phases can be defined, and each may be applied to documents or parts or both.
PDXpert software generally follows the enumerations² in
the IPC-2570 standards, which other PLM software suppliers also use.
These phases are specified by IPC-2570 but aren't defined, presumably because each
organization will create its own set of business rules.
Here are a few examples of item lifecycle phases with business rules:
- Design Document intended for internal use only.
It is not approved for external distribution and may not be used to acquire
parts.
- Prototype Information and the items created from
it may only be used in very limited quantities to validate the design.
- Pilot Part may be acquired in limited quantities
for proof-of-concept production, product support, and field testing.
- Production Product design information may be used
to produce items without restriction.
- Service-only Part may not be used for new
designs. Part may only be purchased for servicing previously produced items.
- Obsolete Item may not be used for any
purpose.
Prototype ("alpha") and Pilot ("beta") phases
in particular are often assigned more specific business rules regarding
maximum quantity permitted, design approvals required, and tooling and
fixture decisions. Contractual obligations or marketing policies may dictate business rules,
such as setting tight inventory stock thresholds and tooling availability, for items at
a Service-only
phase. The Obsolete phase may
incorporate
disposal & recycling business rules, and inventory write-off procedures. Clearly, each company will approach the set of
lifecycle phase definitions according to product complexity, industry norms,
marketing considerations and internal accounting policies.
Item lifecycle business rules are only applied by the organization and its
supply chain partners to currently-released item
revisions, and are irrelevant to pending and canceled revisions.
Relative maturity of an item lifecycle phase
PDXpert software defines a relative
maturity lifecycle attribute, which we believe can be very useful.
The relative maturity value allows you to test whether a child item on a BOM has
a lifecycle phase that's compatible with its parent.
By definition, a zero value represents unrestricted production. Negative
values are pre-production, and positive values are post-production. For example, a component at a
Prototype lifecycle (RM=-20) should not be used on an assembly
at a Production lifecycle (RM=0); however, the relation would be valid if a
Production component was used on a Prototype assembly. Likewise,
an item at Service-only phase (RM=+60) obviously should not be used on a
Production (RM=0) assembly, but the reverse is perfectly acceptable.
Benefits of keeping revision states and lifecycle phases separate
In many older engineering document control processes, an engineering drawing
revision did double duty, indicating both a specific technical iteration and the
business rules currently applicable to the engineering drawing. Numeric ("01"), dash
("-"), and date ("22 Oct 1992") formats were recommended³ prior to production release,
and alphabetic revisions ("A") were used for production revisions. In the
pre-computer era, this was understandable because methods for informing a item's
user of its lifecycle phase
were quite limited and lifecycle business rules weren't terribly
sophisticated.
However, one paid a significant price for this scheme:
- At the critical moment of moving the product into production, every
engineering drawing had to be modified to change the pre-production revision format to production format. At a project's most critical
juncture, the last thing you want to do is run every drawing though the CAD
system one more time to update the revision block. It's a time-consuming
distraction that adds little value and,
with an unnoticed flick of the mouse, can actually damage
previously-validated information.
- There was a practical limit to the number of lifecycle phases that could
be represented by a pre-production drawing revision and, in most cases,
there was no ability to distinguish any lifecycle phase after production.
- Within a specific lifecycle phase, changing a drawing revision indicated
that the technical contents of the document had changed. But changing the
revision format to indicate a new lifecycle phase left an ambiguity: did the
document contents change at the same time as the lifecycle phase changed?
By separating the item revision from its lifecycle phase, PDXpert
PLM software avoids these difficulties. Importantly, a single revision format
can now be used through the item's lifecycle. Incrementing the revision value
exclusively indicates an interchangeable change to a physical part, or a change
which affects only the document contents. The engineering document process can
also support an unlimited number of lifecycle phases anywhere between item
concept and obsolescence, with each phase having a distinct set of business
rules.
While PDXpert software can correctly increment separate
pre-production and production revision formats (and can support manual revision
formats like dash and date), there is no longer any reason to maintain more than
one revision format over the life of an item.
071111.1930