# Metadata collision groups

An object is something representing an entity, and this representation is comprised of a group of files and folders with a specific structure. One such entity is what **LIBSAFE** calls an object.

When we try to preserve an object in an ingestion job, it could happen that the object to be ingested is related to an object already preserved in the system. This happens when the metadata of the object to be ingested and the metadata of the object already preserved determine (through some of its descriptors) that they are indeed the same object.

A collision group is a set of descriptors (one per schema) that establishes a relation between objects which share a descriptor with the same value, which leads to the consideration that they correspond to the same object.

**LIBSAFE** lets us define two types of groups:

1. Unicity.
2. Versioning.

{% hint style="info" %}
**Note**: it is important to point out the metadata associated to these groups can belong to the same or different metadata schemas, with schemas used in the same or different preservation plans, belonging to the same or different preservation areas. The association of every metadata to a group is what lets us identify the collision and thus ensure that any object will be reviewed against all the other existing objects, so that it will not be repeated in the system.
{% endhint %}

Obviously, the latter is only possible if we make sure that we identify objects correctly with their metadata, since if we ingest objects in the system without any defined metadata it is not possible to establish any relation among them.


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