# Shared Database Platform in CSDM

> A shared PostgreSQL platform in CSDM 5: one Technology Management Service Offering, two Application Services on one cluster, one of them outside the offering.

Canonical: https://mikereams.com/diagrams/shared-database-platform-csdm-model

Category: Technical Architecture  
Notation: CSDM 5 (Blueprint Modeler)  
Updated: 2026-10-04  
Author: Mike Reams (https://mikereams.com/about)

![CSDM model of a shared database platform, drawn in Blueprint Modeler. The Technology Management Service Database hosting has the offering PostgreSQL — production, which contains the Application Service Inventory — production. The Business Capability Data management is provided by the Business Applications Inventory and Reporting, which use the Application Services Inventory — production and Reporting — production. Both services depend on the application PostgreSQL cluster, which runs on hosts pg-node-01 and pg-node-02; Inventory — production also depends on the Data-center network.](https://mikereams.com/figures/shared-database-platform-csdm-model.png)

This is the Modeler's own “Shared Database Platform” example, laid out for the page and exported from the same code that draws the canvas in [Blueprint Modeler](https://model.mikereams.com), so every element and relationship is one the CSDM 5 metamodel allows. It is the platform-team view: a database team offers PostgreSQL to the rest of the company, and two application teams build on it, one of them officially.

## Reading it top to bottom

**Business and design layers.** The capability “Data management” is provided by two Business Applications, “Inventory” and “Reporting.” Each uses one Application Service, “Inventory — production” and “Reporting — production.” Nothing unusual so far; the interesting part is what the two services share.

**Service layer, platform side.** The database team is a Technology Management Service, “Database hosting,” with the offering “PostgreSQL — production.” That offering contains Inventory — production. It does not contain Reporting — production, and the Modeler raises a hint for a service with no offering above it. That gap is the example's lesson: Reporting consumes the platform without being in the platform's contract, so the database team's maintenance calendar has no reason to mention it.

**Functional and infrastructure layers.** Both services depend on one Application CI, the “PostgreSQL cluster,” which runs on pg-node-01 and pg-node-02. Inventory — production also depends on the “Data-center network,” a Network CI, which is the kind of dependency teams forget until the switch firmware changes.

## What the shape buys you

- Shared risk made visible. If pg-node-01 fails, the walk reaches the cluster, then both production services, then the offering and both applications, then the capability and the technology service: eight of eight elements in four hops. The model says so because “Runs on” says so. If the cluster is meant to survive a node, model the cluster that way; a blast radius is only as honest as its relationships.
- A contract you can point at. The offering is where the database team's promises live: hours, backup, change windows. Every service inside it inherits them, and every service outside it, like Reporting, is a conversation waiting to happen.
- Cost with somewhere to land. A shared platform's cost is allocated through its offering to the services it contains. A consumer that is not in the offering is also not in the bill, which finance notices before architecture does.

## Try it yourself

Open [Blueprint Modeler](https://model.mikereams.com), choose Examples › Application architecture › Shared Database Platform, and right-click any element for Show blast radius. The model file behind this figure is [available to download](https://mikereams.com/figures/shared-database-platform-csdm.blueprint.json) and imports with Import… in the toolbar. Nothing here is a real system; the names are the example's.

## Sources

- [Blueprint Modeler class guide (classes, relationships and hints, each with its ServiceNow source)](https://model.mikereams.com/guide)
- [CSDM 5 white paper (ServiceNow Community)](https://www.servicenow.com/community/s/cgfwn76974/attachments/cgfwn76974/common-service-data-model-kb/744/3/CSDM%205%20w%20links.pdf)

## Related

- Writing: [Why You Can't Answer "What Does This App Cost?"](https://mikereams.com/writing/why-you-cant-answer-what-does-this-app-cost)
- Writing: [The Missing Middle: Why Business Apps Shouldn't Point at Servers](https://mikereams.com/writing/the-missing-middle-why-business-apps-shouldnt-point-at-servers)
- Work: [Blueprint Modeler: A Free CSDM Architecture Canvas](https://mikereams.com/work/blueprint-modeler)