What is the CMDB in ServiceNow?

A federated database of Configuration Items (CIs) and their relationships, rooted at cmdb_ci. Every CI class extends cmdb_ci, inheriting its columns and behavior.

What is the parent table of every CI class?

cmdb_ci. All CI classes (server, database, application, business service, etc.) extend it, so a query against cmdb_ci returns every CI regardless of class.

What is the CI Class Manager?

A modeling UI that lets admins view, extend, and edit CI classes, attributes, identification rules, and reconciliation rules without writing SQL — the canonical place to manage class-level configuration.

What is CMDB Data Manager?

A governance app for scheduled CI lifecycle actions (retire, delete, orphan cleanup) driven by policies, not one-off scripts.

You need to add a 'lease_expiry' field on Windows servers. Do you extend cmdb_ci_win_server or create a custom table?

Add columns to the existing OOB class via CI Class Manager; this preserves identification rules and inheritance. Never create a parallel u_windows_server table — you'd lose OOB identification, reconciliation, and Discovery mapping. Prefix custom columns with u_ so upgrades don't clash. Alternate: Alternate: create a scoped application table that references the OOB CI (cmdb_ci_win_server) via a reference field — good when the data is app-specific rather than a CI property. Pitfall: Extending too deep in the tree forces every subclass to inherit the column. Extend at the lowest class that needs it.

Discovery Interview · Hub

DISCOVERY &
CMDB DEEP DIVE.

14 focused sub-modules — each with curated definitive Q&A, scenario drills, and a one-click AI expander so you can grow the list toward 100+ questions per section as you study.

01
CMDB
How the Configuration Management Database is structured, extended, and governed.
02
Discovery
How ServiceNow Discovery finds infrastructure and populates the CMDB.
03
MID Servers
The Java-based agent that brokers Discovery and integrations.
04
IRE
The single entry point for every CI write.
05
CIs
What a CI is, what attributes matter, and how CIs are keyed.
06
CI Classes & Tables
How class hierarchy, table extension, and table-per-hierarchy work.
07
Relationships & Dependencies
How CIs relate and how impact propagates.
08
Service Mapping
Mapping business services from entry points down.
09
Integrations & Imports
Getting CI data in from external systems.
10
CI Lifecycle
Onboarding, updating, and retiring CIs by policy.
11
CMDB Health
Measuring completeness, correctness, and compliance.
12
ITSM Integration
How the CMDB powers impact, CAB, and RCA.
13
CSDM
The prescriptive blueprint for CMDB modeling.
14
HAM & SAM
Asset lifecycle, contracts, entitlements, and reclamation.

Also useful

Discovery starter guide CMDB + CSDM basics Scenario scripting

CMDB

Discovery

MID Servers

IRE

CIs

CI Classes & Tables

Relationships & Dependencies

Service Mapping

Integrations & Imports

CI Lifecycle

CMDB Health

ITSM Integration

CSDM

HAM & SAM

Also useful