There areseveral types of ERNs (or ECNs as some prefers)

• ERN that is related to engineering changes on a single Part and the documentation related to the Part
• ERN that is related to the Product Structure Parts and that deals with adding or deleting Parts in the Product Structure Parts.
• ERN that is related to the Product Structure Variants and that deals with changes here including the adding and deleting of Variants/Options and the release and termination of these.

It may be even more but I mention these as examples

The PDM application shall of course be able to support Product Engineering while the ERN/ECN is created, released and effected in Manufacturing. All released ERNs shall be recorded and stored in the PDM databases "for ever" or for as long as it is interesting to keep any information about the Nominal Product and the pertaining Engineering Change History. 

Definition of an ERN related to Product Structure Parts

An ERN should describe

• An Engineering Change related to the Product Structure where Parts are deleted and Parts are added. Sometimes the added Parts are replacing the deleted Parts.
• A Part Version Change where Part is changed without loosing it's interchangeability.
• A Part Version Document Change is a change to the documents defining and describing the actual Part Version. Such documents may be the Drawing, the Geometric Model and other documents defining or describing the Part Version with all its dimensions and properties. A Documentation Change may not always affect the FFF (Form, Fit, Function) of a Part.

The Engineering Changes should always be related to the representation of the Nominal Product or the Assembly or Module or the Documentation on which is presented. This should be applied for Part Version Changes as well: realize the significance between representations of the physical world (Products, Parts etc.) and the Documents on which they are described or specified.

Engineering Changes related to the Product Structure.

An ERN has an impact on the Nominal Product and the documentation of these in PDM applications. It is normally issued by Product Engineering. It should always be based on requests for changes in the (Nominal) Products: ECR (Engineering Change Request).

The ERN will have an impact on Manufacturing:

• New Parts,
• new Variants/Options or
• Part Versions replacing the previous ones or
• Parts or Variants/Options which have become obsolete and should be deleted.

It will have an impact on the After Market:

• old and new Spare Parts,
• revised Manuals and Parts catalogues.

The decision and reporting of when an Engineering Change should be effected and
for which Product/Model/Variant and at which Plant is of course essential.

It gets more complicated when changes to components manufactured in different Plants or at Partners shall have to be coordinated with changes to the End Products in several Plants around the world with very different lead time for logistics.

Our PDM applications must be able to cope with this. The effectivity of Engineering Changes even affects other applications than the PDM applications. It is normal to record the effectivity of Engineering Changes in Spare Parts applications and applications that handle claims and campaigns (see Views and Life Cycles).

Engineering Changes are definitely part of the PSR and the Product Structure (see explanation under Engineering BoM).

The PSR is not fully defined until the ERN with its Effectivity tells whether the PSR is released by which ERN and for witch Plant and from which point in time it should be effected.

The ERN is normally a separate report/document generated from the database at the release of the ERN used to display all changes related to the ERN. The ERN should normally be a "Technically related and coordinated Change" that can be treated as one event in the life of a certain Product or range of Products. An ERN has an identifier or a number in order to be able to treat them as unique occurrencies. However, an ERN should also be an integrated part of the PDM and the Engineering BoM. The ERN Report can be regarded a special "View" of the Product Structure related to the Engineering Change.

Engineering Changes related to Part Version.

There are ERNs that are related to the Parts and its Versions only.

Such an ERN should describe the difference between the current Part Version and the Part Version replacing it.

Axiom: Unless the Enterprise has a way to differentiate Part Versions by serial no or version no of the same Part in manufacturing, it will not be possible to define or decide Effectivity for these Engineering Changes. Different Part Versions may be mixed in the same bin on the shop floor or in the storeroom. The rule is: all Part Versions are interchangable.　

Hence, when FFF is affected:　change Part Number.

Effectivity of an ERN.

If an ERN is related to a Part:

This kind of ECR will not be possible to effect on a certain date or serial number i an End Product. Effectivity may be related to delivery date from vendor or Plant. It may also be possible to reflect Part Version in a Product Instance Database. However, it will take some pretty advanced PDM and MRP applications and strict reporting procedures to be able to achieve this.

If an ERN is related to the Product Structure:

The Effectivity is part of the PSR: unless it is specified from which date a certain PSR is valid for which Plants, it is not fully specified. The Effectivity may be from a certain date for a Plant without any expiration date or a date for the expiration may be given (but normally for a different ERN).

NB! If the same Product, Assembly or Part is being manufactured at several Plants, it is necessary that the PDM applications can cope with different Effectivity for an ERN and the Products/Variants/Options at hand for the different Plants. This is not necessary for a Plant that is just assembling prepacked complete kits.