The Ultimate ServiceNow CIS-DF (Data Foundations) Exam Cheat Sheet

Critical Table Distinctions

• Business Application (cmdb_ci_business_app): The inventory record (e.g., “Zoom”). Non-operational. You cannot open an incident against this.
• Application Service (cmdb_ci_service_auto): The deployed instance (e.g., “Zoom – Production”). Operational. Incidents live here.
• Dynamic CI Group (cmdb_ci_query_based_service): A wrapper CI that groups CIs based on a query (e.g., “All Linux Servers in NY”).

CSDM 4.0 Lifecycle Standards

Stop using install_status or operational_status. The new standard uses two fields on cmdb_ci:

1. lifecycle_stage (e.g., Operational, End of Life)
2. lifecycle_stage_status (e.g., In Use, Retired, Obsolete)

Exam Tip: You must use the CSDM Lifecycle Mapping tool to map legacy status fields to these new standard fields. The system then keeps them in sync automatically.

⚙️ 2. Identification & Reconciliation Engine (IRE)

The “Gatekeeper” that prevents duplicates and manages data source priority.

The IRE Processing Order (Crucial!)

You must know the exact order in which the IRE processes a payload:

1. Input Payload: JSON arrives (Discovery, Import Set, etc.).
2. Identification Rules: “Does this CI exist?”
   • Checks Class priority (e.g., Serial Number -> Name + Mac Address).
   • Match = Update / No Match = Create.
3. Reconciliation Rules: “Is this source allowed to update this attribute?”
   • Checks Data Source Precedence.
   • Example: ServiceGraph-SCCM (Priority 100) vs. Manual (Priority 500). Lower number wins.
4. IRE Data Refresh Rules: “Is the high-priority data stale?”
   • Allows a lower-priority source to update a locked field if the primary source hasn’t reported in X days.
5. Multi-Source CMDB: Updates sys_object_source history.

Key IRE Concepts

• sys_object_source Table: The “Rosetta Stone.” Maps a Native Key (e.g., SCCM Resource ID) to a ServiceNow Sys ID.
• Independent CIs: Can exist alone (Server, Switch).
• Dependent CIs: Cannot exist without a parent (Network Card, Hard Drive). Identified by Parent ID + Local Attribute.
• De-Duplication: If IRE finds two matches for one payload, it halts. It creates a De-duplication Task and does not update the records.

3. CMDB Health Dashboard

The “Vital Signs” calculated via scheduled jobs.

The 3 “C”s Metric Categories

1. Completeness (Are fields filled?)

• Required: Mandatory in System Dictionary (Global).
• Recommended: Marked in CI Class Manager (Soft check).

2. Correctness (Is data accurate?)

• Duplicate: Based on Identification Rules.
• Orphan:
  • Logical: Item missing required data (e.g., Virtual Machine missing a “Virtual” flag).
  • Relationship: Dependent CI (NIC) lost its Parent (Server).
• Staleness: CI not updated in X days (Default: 60).

3. Compliance (Does it follow rules?)

• Uses Audits and Desired State to check logical conditions (e.g., “All Prod Servers must have 16GB RAM”).

4. CMDB Data Manager

The modern way to handle Lifecycle (Retire/Archive/Delete).

This replaces the legacy “Data Certification” plugin for lifecycle management. It is policy-driven.

1. Policy: Filter criteria (e.g., “Servers not discovered in 6 months”).
2. Action:
   • Retire: Set status to Retired.
   • Archive: Move from cmdb_ci to ar_cmdb_ci (Flattened, read-only storage).
   • Delete: Permanently destroy.
3. Attestation: Send a task to the CI Owner to verify the CI before taking action.

5. Advanced Concepts & Gotchas

CMDB 360 (Multisource CMDB)

• Problem: Discovery says RAM is 8GB. SCCM says 16GB. Who is right?
• Solution: CMDB 360 stores every value submitted by every source in the cmdb_multisource_data table.
• Use Case: You can revert a specific field to a previous value from a specific source without re-running discovery.

Principal Class Filter

• Concept: There are too many CIs in the cmdb_ci table (Printers, Routers, Mice).
• Feature: The “Principal Class” filter limits what users see in reference fields (like on the Incident form) to only the “Big” CIs (Servers, Apps, Databases).

Service Graph Connectors (SGC)

• Rule: Always prefer SGC over custom Import Sets.
• Why: They come with pre-built IRE mappings and class structures certified by ServiceNow.

Exam Strategy Summary

• Think like an Architect: Don’t just answer how to configure it; answer why (Governance, minimizing technical debt).
• IRE is King: If you don’t understand how Identification and Reconciliation rules interact, you will struggle.
• CSDM is the Map: Know which table belongs to which domain and which Persona manages it.

Good luck with your CIS-DF!