Relationship Mapping

CI Relationship Mapping

Overview

CI relationships form the backbone of CMDB value. Without relationships, CIs are isolated islands of data. This skill covers:

• Understanding relationship types and their semantics
• Creating and validating relationships between CIs
• Analyzing dependency chains for impact assessment
• Detecting orphan CIs that lack relationships
• Maintaining relationship health over time

When to use: When modeling service dependencies, preparing for change impact analysis, auditing CMDB completeness, or troubleshooting service outages.

Value proposition: Well-mapped relationships enable accurate impact analysis, reducing change failures by up to 50% and decreasing MTTR during incidents.

Prerequisites

• Roles: cmdb_admin or itil with CMDB write access
• Access: cmdb_rel_ci, cmdb_rel_type, cmdb_ci tables
• Knowledge: CI class hierarchy, dependency modeling concepts
• Related skills: Complete cmdb/ci-discovery first

Procedure

Step 1: Understand Relationship Types

ServiceNow provides relationship types in cmdb_rel_type. Each relationship has:

• Parent descriptor: How the parent relates to the child
• Child descriptor: How the child relates to the parent

Common Relationship Types:

Query available relationship types:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_type
  query: active=true
  fields: sys_id,name,parent_descriptor,child_descriptor
  limit: 100

REST API:

GET /api/now/table/cmdb_rel_type?sysparm_query=active=true&sysparm_fields=sys_id,name,parent_descriptor,child_descriptor&sysparm_limit=100

Step 2: Query Existing Relationships

Before creating relationships, understand what exists:

Find all relationships for a CI:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_ci
  query: parent=[ci_sys_id]^ORchild=[ci_sys_id]
  fields: parent,child,type,sys_created_on
  limit: 50

Find downstream dependencies (what depends on this CI):

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_ci
  query: child=[ci_sys_id]^type.parent_descriptorLIKEDepends
  fields: parent,parent.name,type,type.parent_descriptor

Find upstream dependencies (what this CI depends on):

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_ci
  query: parent=[ci_sys_id]^type.parent_descriptorLIKEDepends
  fields: child,child.name,type,type.child_descriptor

Step 3: Create Relationships

Determine the correct relationship type first:

Decision Matrix:

Find relationship type sys_id:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_type
  query: nameLIKERuns on::Runs on
  fields: sys_id,name,parent_descriptor,child_descriptor

Create the relationship:

Tool: SN-Create-Record
Parameters:
  table_name: cmdb_rel_ci
  data:
    parent: [parent_ci_sys_id]
    child: [child_ci_sys_id]
    type: [relationship_type_sys_id]

Example - Application runs on Server:

Tool: SN-Create-Record
Parameters:
  table_name: cmdb_rel_ci
  data:
    parent: "abc123..."  # Application CI sys_id
    child: "def456..."   # Server CI sys_id
    type: "55c95bf6c0a8010e0118ec7056e1c57d"  # Runs on::Hosts

Step 4: Validate Relationships

Check for invalid relationships:

Find relationships with missing CIs:

Tool: SN-Execute-Background-Script
Parameters:
  description: Find invalid relationships with missing CIs
  script: |
    var gr = new GlideRecord('cmdb_rel_ci');
    gr.addQuery('parent.sys_idISEMPTY^ORchild.sys_idISEMPTY');
    gr.query();
    gs.info('Invalid relationships found: ' + gr.getRowCount());
    while (gr.next()) {
      gs.info('Invalid rel: ' + gr.sys_id + ' parent=' + gr.parent + ' child=' + gr.child);
    }

Find duplicate relationships:

Tool: SN-Execute-Background-Script
Parameters:
  description: Detect duplicate relationships
  script: |
    var duplicates = new GlideAggregate('cmdb_rel_ci');
    duplicates.addAggregate('COUNT');
    duplicates.groupBy('parent');
    duplicates.groupBy('child');
    duplicates.groupBy('type');
    duplicates.addHaving('COUNT', '>', 1);
    duplicates.query();
    gs.info('Duplicate relationship combinations found: ' + duplicates.getRowCount());
    while (duplicates.next()) {
      gs.info('Duplicate: parent=' + duplicates.parent + ' child=' + duplicates.child + ' type=' + duplicates.type + ' count=' + duplicates.getAggregate('COUNT'));
    }

Validate relationship type appropriateness:

Some relationship types are only valid for certain CI classes. Check the relationship type's parent_ci_class and child_ci_class fields if populated.

Step 5: Analyze Dependency Chains

Understanding full dependency chains is critical for impact analysis.

Get complete dependency tree (recursive):

Tool: SN-Execute-Background-Script
Parameters:
  description: Build dependency tree for CI
  script: |
    var ciSysId = 'YOUR_CI_SYS_ID';
    var maxDepth = 5;
    var visited = {};
    var tree = [];

    function getDependencies(parentId, depth, direction) {
      if (depth > maxDepth || visited[parentId]) return;
      visited[parentId] = true;

      var gr = new GlideRecord('cmdb_rel_ci');
      if (direction === 'down') {
        gr.addQuery('child', parentId);
        gr.addQuery('type.parent_descriptor', 'CONTAINS', 'Depends');
      } else {
        gr.addQuery('parent', parentId);
        gr.addQuery('type.parent_descriptor', 'CONTAINS', 'Depends');
      }
      gr.query();

      while (gr.next()) {
        var targetId = direction === 'down' ? gr.parent.toString() : gr.child.toString();
        var targetName = direction === 'down' ? gr.parent.name.toString() : gr.child.name.toString();
        tree.push({
          depth: depth,
          direction: direction,
          ci_name: targetName,
          ci_sys_id: targetId
        });
        getDependencies(targetId, depth + 1, direction);
      }
    }

    getDependencies(ciSysId, 1, 'down');
    gs.info('Upstream dependencies (what depends on this CI):');
    tree.forEach(function(item) {
      gs.info('  '.repeat(item.depth) + item.ci_name);
    });

Identify critical path:

Services with single points of failure have critical paths:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_ci
  query: parent.sys_class_name=cmdb_ci_service^type.parent_descriptorLIKEDepends
  fields: parent.name,child.name,child.sys_class_name

Step 6: Detect Orphan CIs

Orphan CIs (those without relationships) reduce CMDB value and complicate impact analysis.

Find CIs with no relationships:

Tool: SN-Execute-Background-Script
Parameters:
  description: Find orphan CIs with no relationships
  script: |
    var orphans = [];
    var ciClasses = ['cmdb_ci_server', 'cmdb_ci_appl', 'cmdb_ci_database_instance'];

    ciClasses.forEach(function(ciClass) {
      var gr = new GlideRecord(ciClass);
      gr.addQuery('operational_status', '1');
      gr.query();

      while (gr.next()) {
        var relGr = new GlideRecord('cmdb_rel_ci');
        relGr.addQuery('parent', gr.sys_id);
        relGr.addOrCondition('child', gr.sys_id);
        relGr.setLimit(1);
        relGr.query();

        if (!relGr.hasNext()) {
          orphans.push({
            sys_id: gr.sys_id.toString(),
            name: gr.name.toString(),
            class: ciClass
          });
        }
      }
    });

    gs.info('Orphan CIs found: ' + orphans.length);
    orphans.forEach(function(o) {
      gs.info('  ' + o.class + ': ' + o.name + ' (' + o.sys_id + ')');
    });

MCP Alternative - Query-based approach:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_ci_server
  query: operational_status=1^sys_idNOT IN(SELECT parent FROM cmdb_rel_ci)^sys_idNOT IN(SELECT child FROM cmdb_rel_ci)
  fields: name,ip_address,sys_class_name
  limit: 50

Note: Complex subqueries may not work via REST API. Use background script for reliability.

Step 7: Maintain Relationship Health

Periodic cleanup script:

Tool: SN-Execute-Background-Script
Parameters:
  description: Clean up invalid relationships
  script: |
    var deleted = 0;

    // Delete relationships where parent CI was deleted
    var gr = new GlideRecord('cmdb_rel_ci');
    gr.addNullQuery('parent');
    gr.query();
    while (gr.next()) {
      gr.deleteRecord();
      deleted++;
    }

    // Delete relationships where child CI was deleted
    gr = new GlideRecord('cmdb_rel_ci');
    gr.addNullQuery('child');
    gr.query();
    while (gr.next()) {
      gr.deleteRecord();
      deleted++;
    }

    gs.info('Deleted ' + deleted + ' invalid relationships');

Update stale relationships: When a CI's operational status changes, relationships may need updates:

Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_ci
  query: parent.operational_status!=1^ORchild.operational_status!=1
  fields: sys_id,parent.name,child.name,parent.operational_status,child.operational_status

Tool Usage Summary

Best Practices

• Bidirectional Awareness: Remember relationships have two perspectives (parent/child)
• Minimum Relationships: Every operational CI should have at least one relationship
• Type Consistency: Use consistent relationship types across similar CI patterns
• Avoid Circular Dependencies: A should not depend on B if B depends on A
• Document Business Context: Use relationship attributes to explain why the relationship exists
• Regular Audits: Run orphan detection monthly; invalid relationship cleanup weekly
• Discovery Integration: Align manual relationships with discovery-created relationships

Troubleshooting

Relationship Not Showing in Dependency View

Symptom: Created relationship doesn't appear in CI dependency views Cause: Relationship type not configured for dependency visualization Solution: Check cmdb_rel_type record - ensure is_used_by and is_dependency flags are set appropriately

Duplicate Relationships After Discovery

Symptom: Same relationship exists multiple times Cause: Manual creation overlapped with discovery Solution: Run duplicate detection script; delete duplicates keeping discovery-created records

Circular Dependency Detected

Symptom: Impact analysis shows infinite loop warning Cause: CI A depends on B, B depends on C, C depends on A Solution: Review and break the circular chain; often indicates incorrect relationship type usage

Relationship Type Not Found

Symptom: Cannot find appropriate relationship type for use case Cause: OOB types may not cover all scenarios Solution: Create custom relationship type via cmdb_rel_type table (requires cmdb_admin)

Examples

Example 1: Map a Three-Tier Application

# 1. Identify the CIs
Business Service: "Customer Portal"
Web Application: "Portal Frontend"
App Server: "prod-app-01"
Database: "Portal DB"
DB Server: "prod-db-01"

# 2. Find relationship type sys_ids
Tool: SN-Query-Table
Parameters:
  table_name: cmdb_rel_type
  query: nameLIKEDepends on^ORnameLIKERuns on
  fields: sys_id,name,parent_descriptor

# 3. Create relationships (batch in one message)
# Service depends on Web App
SN-Create-Record: cmdb_rel_ci
  parent: [service_sys_id], child: [webapp_sys_id], type: [depends_on_type]

# Web App runs on App Server
SN-Create-Record: cmdb_rel_ci
  parent: [webapp_sys_id], child: [appserver_sys_id], type: [runs_on_type]

# Web App depends on Database
SN-Create-Record: cmdb_rel_ci
  parent: [webapp_sys_id], child: [database_sys_id], type: [depends_on_type]

# Database runs on DB Server
SN-Create-Record: cmdb_rel_ci
  parent: [database_sys_id], child: [dbserver_sys_id], type: [runs_on_type]

Example 2: Orphan Detection and Remediation

# 1. Find orphan servers
Tool: SN-Execute-Background-Script
Parameters:
  script: [orphan detection script from Step 6]

# 2. For each orphan, determine what it hosts
Tool: SN-Query-Table
Parameters:
  table_name: cmdb_ci_appl
  query: install_dateLIKE[orphan_ip_address]
  fields: name,sys_id

# 3. Create missing relationships
Tool: SN-Create-Record
Parameters:
  table_name: cmdb_rel_ci
  data:
    parent: [app_sys_id]
    child: [orphan_server_sys_id]
    type: [runs_on_type_sys_id]

Related Skills

• cmdb/ci-discovery - CI creation and classification
• cmdb/impact-analysis - Using relationships for impact analysis
• cmdb/data-quality - CMDB data quality management
• itsm/change-management - Changes and CI relationships

References

• ServiceNow CMDB Relationships
• CMDB Relationship Types
• ITIL Configuration Management
• ServiceNow CMDB Best Practices