Configuration Management Database (CMDB)
About 5% of the CIS-ITSM exam — see all 6 domains.
Purpose
The CMDB is the trusted record of Configuration Items (CIs) and their relationships, underpinning impact analysis, change conflict detection, and service mapping. The lowest-weighted domain, but the exam still expects core literacy.
Data model
CIs are stored in classes that extend the base cmdb_ci table; specific classes (server, application, network gear, etc.) extend it in an inheritance hierarchy. CI relationships are stored in cmdb_rel_ci and describe dependencies (Runs on, Depends on, Hosted on) that power impact maps. The Common Service Data Model (CSDM) is ServiceNow's prescribed framework for modeling services and applications consistently (business/technical/application services, business applications) — populate the CMDB to align with CSDM.
IRE — Identification and Reconciliation Engine
The Identification and Reconciliation Engine (IRE) is the single entry point that keeps the CMDB clean:
- Identification rules decide whether an incoming CI already exists (using identifier entries/criteria). If matched, the existing record is updated; if not, a new CI is created — this prevents duplicates.
- Reconciliation rules decide which data source is authoritative for which attributes, so that, for example, Discovery can be trusted over a manual edit for certain fields.
Data enters the CMDB via Discovery, integrations, Service Mapping, IntegrationHub ETL, and manual entry — all funneled through IRE so the same identification/reconciliation logic applies.
Exam focus
- CMDB = CIs + relationships; CIs extend
cmdb_ci; relationships incmdb_rel_ci. - CSDM is the modeling framework to align to.
- IRE: identification rules prevent duplicates (match/update vs. insert); reconciliation rules pick the authoritative source per attribute.
- CMDB feeds change conflict detection and incident/problem CI context.
Sample questions from this domain
Three of the 15 in this domain, with the reasoning. The full set is in the question bank.
What is the primary purpose of the CMDB in ServiceNow?
- A. To store configuration items (CIs) and their relationships as a single source of truth for the IT environment ✓
- B. To approve changes
- C. To restore service after outages
- D. To author knowledge articles
Why: The CMDB stores CIs and their relationships, providing a single source of truth that supports ITSM processes. Restoring service (B) is Incident Management, approving changes (C) is Change Management, and authoring knowledge (D) is Knowledge Management.
Which base table do most configuration item classes extend in ServiceNow?
- A. incident
- B. sys_user
- C. cmdb_ci ✓
- D. task
Why: Most CI classes extend cmdb_ci, the base configuration item table. The task table (B) is the base for process records like incidents, while incident (C) and sys_user (D) are unrelated to the CI hierarchy.
Which CMDB capability prevents duplicate CIs by matching incoming data against existing records using defined identifier criteria?
- A. Identification and Reconciliation (IRE) with identification rules ✓
- B. SLA definitions
- C. Inbound email actions
- D. Catalog UI policies
Why: The Identification and Reconciliation Engine (IRE) uses identification rules to match incoming data to existing CIs and prevent duplicates. SLA definitions (B), inbound email actions (C), and catalog UI policies (D) are not involved in CI identification.