TADDM Globally Unique Identifiers

Identification values are commonly referred to as globally unique identifiers (GUIDs). The TADDM GUIDs are built according to UUID version 3 specification (IETF Standards Track RFC 4122), and are used as identifiers of configuration items (CIs).

Version 3 GUIDs are generated by processing a string with an MD5–type cryptographic algorithm. TADDM passes a string that is constructed from the values of the attributes that are used in the naming rules to the GUID generation component. Most CIs have multiple naming rules and can therefore generate multiple GUIDs. The attribute values that are available when the CI is created determine which GUIDs are generated. Generally, the first GUID that is generated for an object is considered the master GUID or primary identifier for that object. Other generated GUIDs are aliases of the master GUID.

If the CIs are discovered with the same attributes and values, they always have the same set of GUIDs. However, the first GUID, which later becomes a master GUID, is generated randomly. That is why a particular CI might not have the same master GUID on different TADDM installations. Likewise, it might not be chosen again when the item is deleted or the database is re-created. The same types of CIs, such as ComputerSystems, might also use GUIDs that are calculated from a different naming rule than their master GUIDs.

Generally, TADDM application programming interfaces (APIs) identify CIs by their master GUIDs, but they can also identify them by their aliases. That is why, if you want to find a particular CI, you can search for it by using its alias GUID.

GUID erosion

GUIDs that are aliases of a master GUID might erode during the lifecycle of a configuration item. Erosion happens when an attribute that defines a single naming rule, such as a signature, changes. After this change, a new set of GUIDs is generated, and replaces the old values. If the attributes of a master GUID change, this GUID remains the same and a new alias is added.

Master GUID changes

A master GUID of a particular configuration item can change due to any of the following conditions:
Deletion of a configuration item, and rediscovery
When a configuration item is deleted from the TADDM database, a different GUID might be chosen as a master GUID during the next store of this CI.
Configuration items merge scenario
When new data is available in TADDM, two different CIs might be identified as the same instance. A user can also start the merge manually. In this scenario, the attributes of a transient and a durable CI can merge. As a result, the master GUID of a transient CI becomes a new alias of the durable one, and the master GUID of the durable CI represents a CI that was created after the merge.
TADDM upgrade
When you upgrade to a new version of TADDM, the attributes that are part of naming rules might change. This situation might also affect the data migration process that is supposed to ensure that master GUIDs remain the same after the upgrade. A new version of sensors or Discovery Library Adapters might also change the way the attribute values are stored.