---
sourceDocument: Yokohama IT Operations Management
sourceDocumentLink: https://servicenow-prod.fluidtopics.net/r/yokohama/it-operations-management

 Release :

    - yokohama

ft:locale :

    - en-US

ft:publication_title :

    - Yokohama IT Operations Management

ft:clusterId :

    - itom

bundleId :

    - itom

workflow :

    - Technology


---

# Event identifiers

# Event identifiers {#ariaid-title1}

* Release version: Yokohama
* 
* Updated July 31, 2025
* 
* ![](https://www.servicenow.com/docs/portal-asset/ico-clock) 1 minute to read

Event identifiers uniquely distinguish one event from another. Event Management uses these identifiers to determine whether to create a new alert or update an existing one.

By default, an event is uniquely identified by the following fields:

* Message Key
* Domain
* Category

{#c_EMEventIdentifier__ul_fbv_szj_yhc}

Changing the Category field (for example, through a Background Script or Business Rule) may lead to unexpected system behavior.

If the Message Key is not provided, the system automatically generates one by concatenating the following fields:

* Source
* Type
* Node
* Resource
* Metric Name

{#c_EMEventIdentifier__ul_gbv_szj_yhc}

If the above fields are not defined in the incoming event, you can define them using event rules.