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 store hardware and software asset records used for financial, contract, warranty, and license tracking
- C. To record incidents, problems, and changes against business services so that their SLAs can be measured and reported
- D. To discover devices on the network and schedule recurring scans across the IT environment
Why: The CMDB stores CIs and their relationships, providing a single source of truth that supports ITSM processes. Financial, contract and license tracking of assets is Asset Management, task records and their SLAs live in the ITSM applications and Service Level Management, and scanning the network is what Discovery does to populate the CMDB.
Which base table do most configuration item classes extend in ServiceNow?
- A. alm_asset
- B. task
- C. cmdb_ci ✓
- D. cmdb_rel_ci
Why: Most CI classes extend cmdb_ci, the base configuration item table. The alm_asset table holds asset records that can be linked to CIs, cmdb_rel_ci stores the relationships between CIs, and task is the base table for process records such as incidents and changes.
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. Reconciliation rules that set data source precedence for attributes
- C. CMDB Health correctness checks with duplicate CI audit metrics
- D. Normalization Data Services with manufacturer name normalization
Why: The Identification and Reconciliation Engine (IRE) uses identification rules to match incoming data to existing CIs and prevent duplicates. Reconciliation rules on their own only decide which source may update which attributes after a CI is identified, CMDB Health correctness reports duplicates after they exist rather than preventing them, and Normalization Data Services standardizes manufacturer and product names.