CMDB & Relationships

CMDB Overview

The Configuration Management Database (CMDB) is the central repository for tracking IT assets, their attributes, and how they relate to each other. It is not a separate system — it is simply a collection of tables within ServiceNow's database.

The Base CI Table

Key CI Classes

CI Class Hierarchy

ServiceNow implements CI classification using table inheritance. Each CI class is a table that extends a parent table, inheriting all parent fields while adding its own. This creates a deep, organized hierarchy for every type of IT asset.

Core Inheritance Chain

cmdb_ci                   ← Root base CI table (all CIs)
  └── cmdb_ci_hardware    ← Physical hardware
        └── cmdb_ci_computer  ← Computers (desktops, laptops, servers)
              └── cmdb_ci_server  ← Servers specifically

cmdb_ci
  └── cmdb_ci_appl        ← Software applications

cmdb_ci
  └── cmdb_ci_service     ← Business / IT services

sys_class_name — The CI's True Identity

Because all CI records are stored across extended tables, the sys_class_name field is how ServiceNow (and the platform) knows what type of CI a record actually is. This field is set automatically when a CI is created.

CI Class Manager

The CI Class Manager is a visual tool within ServiceNow that lets administrators browse and manage the CI class hierarchy. Navigate to it via: Configuration > CI Class Manager.

CI Relationships

Relationships define how CIs connect to and depend on each other. They are the backbone of dependency mapping, impact analysis, and service modeling. Without relationships, the CMDB is just a list — with them, it becomes a dynamic map of your IT infrastructure.

The Relationship Table

Relationship Direction: Parent → Child

Every relationship in ServiceNow is directional. It goes from a parent CI to a child CI, and the relationship type provides two labels — one describing it from the parent's perspective and one from the child's perspective. These are called the type and the complement type.

Relationship:  Parent CI  ──[type]──→  Child CI
                                         ↑
                             [complement type] (read from child's perspective)

Example:
  Web Server  ──[Depends on]──→  Database Server
  Database Server  ──[Used by]──→  Web Server  (complement view)

Common Relationship Types

CI Relationship Form

Relationships can be added and viewed directly from the CI record via the Relationships tab (or related list) at the bottom of any CI form. You can also navigate to cmdb_rel_ci.list to see all relationships in the system.

Service Mapping & Discovery

ServiceNow provides two major automated tools for populating and maintaining the CMDB: Discovery (finds individual assets on the network) and Service Mapping (maps end-to-end business service dependencies).

Discovery

Discovery is a ServiceNow application that automatically scans your network, identifies assets, and creates or updates CI records in the CMDB without manual data entry.

What Discovery Populates

• Servers (cmdb_ci_server) — hardware specs, OS, serial numbers
• Network devices — switches, routers, load balancers
• Installed software (cmdb_ci_appl) — applications discovered on servers
• Network adapters and IP addresses — automatically linked to their parent CIs
• Relationships — "Runs on" and "Hosted on" relationships created automatically

Service Mapping

While Discovery finds individual assets, Service Mapping traces the path from a business service down through all its underlying infrastructure components, building a complete dependency map.

Business Service CI (cmdb_ci_service)

A business service is a special CI class (cmdb_ci_service) that represents a service delivered to users — such as "Email Service," "ERP Application," or "VPN Access." Business services sit at the top of the dependency hierarchy and aggregate the health of all their underlying CIs.

CMDB Health

A CMDB is only useful if its data is accurate, complete, and current. ServiceNow provides a suite of tools under CMDB Health to measure and improve data quality.

The Three C's of CMDB Health

Duplicate CIs & Identification Rules (IRE)

One of the most common CMDB health problems is duplicate CI records — the same physical or logical asset having multiple CI records in the CMDB, often caused by multiple data sources (Discovery, manual entry, integrations) creating separate records.

CMDB Health Dashboard

The CMDB Health dashboard provides an at-a-glance view of your CMDB data quality. Navigate to: CMDB > CMDB Health Dashboard. It shows overall scores for completeness, compliance, and correctness — along with drill-down capabilities to identify which specific CI classes and records have issues.

Configuration Items in ITSM

The CMDB is not just a standalone inventory — it is deeply integrated with ServiceNow's ITSM processes. CI records are linked to incidents, changes, problems, and other records to provide context, enable impact analysis, and support decision-making.

The "Configuration Item" Field on Task Records

Many task-based tables in ServiceNow — including Incident, Change Request, and Problem — include a Configuration item field (internally: cmdb_ci). This is a reference field pointing to the CI that is related to or affected by the task.

CI Record — Related Lists

Opening a CI record and scrolling to the bottom reveals related lists that show the CI's ITSM activity at a glance. These related lists pull from ITSM tables filtered by the CI's sys_id.

Key Tables Summary

The following tables are the most important to know for the CSA exam in the context of CMDB. You should be able to identify each table by name and describe its purpose.

Key Exam Facts & Common Traps

This section consolidates the most frequently tested CMDB concepts and common wrong-answer traps on the CSA exam. Study these carefully — they are high-probability exam questions.