The CMDB contains records of configuration items (CIs) and their relationships. A CI is any component that needs to be managed in order to deliver an IT service, such as a server, an application, or a user. A relation type defines the nature of the connection between two CIs, such as depends on, uses, or contains. A model is a template for a CI that defines its attributes and default values. An asset is a tangible or intangible resource that is tracked and managed by the organization, such as a laptop, a license, or a contract.
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Configuration Item (CI) types: Attributes and relationships
What is a configuration management database (CMDB)?
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Reference: https://docs.servicenow.com/bundle/quebec-servicenow-platform/page/product/configuration- management/reference/r_CMDBRecordTypes.html

CMDB Health measures the quality of the data in the CMDB by testing it against predefined rules and metrics. One of the categories of these rules is Correctness, which tests the data against data integrity rules such as identification rules, orphan CI rules, and stale CI rules1. These rules help identify and flag the existing CMDB relationships that are not compliant with the suggested relationships2.
* Duplicate relationships are those that have more than one relationship of the same type between the same two CIs3. For example, if a server CI has two relationships of type "Depends on" with the same network CI, it is a duplicate relationship.
* Stale relationships are those that have not been updated for a specified period of time3. For example, if a server CI has a relationship of type "Runs on" with a virtual machine CI that has not been discovered for more than 60 days, it is a stale relationship.
* Orphan relationships are those that are missing a defined relationship within the CMDB3. For example, if a server CI has no relationship of type "Depends on" with any network CI, it is an orphan relationship.
1: CMDB Health - Customer Success - ServiceNow 2: CMDB health Dashboard: "Relationships not compliant with suggested relationships" calculation -Support and Troubleshooting - Now Support Portal 3: Maintain a healthy CMDB - ServiceNow