The Base Tables
CMDB is built on a class hierarchy rooted at cmdb_ci (Configuration Item). Every CI type extends it — servers, databases, applications, services. Know the hierarchy before you extend it.
Relationships live in cmdb_rel_ci. The parent/child, runs on, depends on, member of relations are the ones you’ll touch most.
Classes Are Hierarchical — Use That
Don’t create flat custom classes. Extend the right ancestor. A custom load balancer class should extend cmdb_ci_lb_service, not cmdb_ci. Extension gives you inherited fields and existing discovery/service mapping patterns.
Identification and Reconciliation
IRE (Identification and Reconciliation Engine) is how ServiceNow decides whether an incoming CI matches an existing one. Misconfigured IRE creates duplicates or overwrites good data. Review identifiers per class; don’t leave defaults in place without checking.
Data Certification
A CMDB without review goes stale in months. Schedule quarterly certification campaigns per CI class. Owners verify their CIs are current, correct, and have required fields populated.
Service Mapping vs Discovery
Discovery finds infrastructure: hosts, processes, network. Service Mapping models logical services that span that infrastructure. Most orgs need both. Start with Discovery; add Service Mapping for your top 20 business services.