CMDB & CSDM
INTERVIEW.

How to answer

• The CMDB is the physical data store — tables under cmdb_ci that hold every Configuration Item and their relationships.
• CSDM (Common Service Data Model) is the prescriptive blueprint for HOW to use those tables — which classes to populate, which relationships to draw, and how services map to applications and infrastructure.
• CSDM 4.0 organizes CIs into four domains: Foundation, Design, Build, and Manage — each stage adds richer service context (from raw hardware to consumable business services).
• You don't 'install' CSDM; you conform to it by populating the right classes (cmdb_ci_service_technical, cmdb_ci_service_offering, cmdb_ci_business_app) with the right relationships.

Reference script

// Sample CSDM-aligned service hierarchy
BusinessApp:   'Payroll'                (cmdb_ci_business_app)
  |-- Depends on -->
Technical Svc: 'Payroll API'            (cmdb_ci_service_technical)
  |-- Depends on -->
Application:   'payroll-api v3.2'       (cmdb_ci_appl)
  |-- Runs on  -->
Server:        'prd-pay-api-01'         (cmdb_ci_linux_server)

// Consumers see the Service Offering, not the tech underneath:
ServiceOffering: 'Payroll — Gold SLA'   (service_offering)
  |-- Offers   --> BusinessApp 'Payroll'

How to answer

• IRE is the single write path into the CMDB — every insert/update from Discovery, Service Graph Connectors, or IntegrationHub goes through it.
• Each CI class has an Identification Rule listing ordered identifier entries (e.g. serial_number, then name+ip_address) — the first match wins.
• Reconciliation Rules decide WHICH data source can update WHICH attribute — so SCCM can own OS version while Discovery owns CPU count without stomping each other.
• Bypassing IRE (direct GlideRecord inserts) is the #1 cause of duplicate CIs — always call the Identification API instead.

Reference script

// Correct — payload goes through IRE
var payload = {
  items: [{
    className: 'cmdb_ci_computer',
    values: {
      serial_number: 'SN-77A31',
      name: 'LT-77A31',
      os: 'Windows 11'
    },
    lookup: []
  }]
};
var ire = new sn_cmdb.IdentificationEngine();
var result = ire.createOrUpdateCI('SCCM', JSON.stringify(payload));
gs.info(result); // { items:[{sysId,operation:'UPDATE'}] }

// WRONG — bypasses IRE, guarantees duplicates over time
// var ci = new GlideRecord('cmdb_ci_computer');
// ci.initialize(); ci.name='LT-77A31'; ci.insert();

How to answer

• Foundation: core reference data (company, location, user, group) — you must have this clean before anything else.
• Design: how services are shaped — Business Application, Information Object, Application Service (logical, non-instantiated).
• Build: pipeline artifacts — Product Model, Software Model, Hardware Model — what you're deploying, not what's running.
• Manage: operational reality — the running instances, Technical Services, Service Offerings, and their supporting infrastructure CIs.

Reference script

// A quick CSDM domain audit — count records per anchor class
var anchors = {
  Foundation: 'core_company',
  Design:     'cmdb_ci_business_app',
  Build:      'cmdb_hardware_product_model',
  Manage:     'cmdb_ci_service_technical'
};
for (var d in anchors) {
  var gr = new GlideAggregate(anchors[d]);
  gr.addAggregate('COUNT');
  gr.query(); gr.next();
  gs.info(d + ': ' + gr.getAggregate('COUNT') + ' records');
}

How to answer

• Completeness: are required attributes populated? Drive this with mandatory fields on Identification Rules and Discovery patterns.
• Correctness: does the data still match reality? Stale records get flagged by the Duplicate Remediator and staleness rules (last_discovered > N days).
• Compliance: does the CI conform to CSDM class + relationship rules? Non-conforming CIs are surfaced in the CMDB Data Manager for cleanup.
• Raise the score by fixing Foundation data first, then tuning IRE identifiers to eliminate duplicates, then adding recurring Discovery schedules for stale CIs.

Reference script

// Query the health dashboard's underlying table
var gr = new GlideRecord('cmdb_health_metric');
gr.addQuery('ci_class', 'cmdb_ci_linux_server');
gr.orderByDesc('sys_created_on');
gr.setLimit(1);
gr.query();
if (gr.next()) {
  gs.info('completeness: ' + gr.getValue('completeness_score'));
  gs.info('correctness:  ' + gr.getValue('correctness_score'));
  gs.info('compliance:   ' + gr.getValue('compliance_score'));
}