Impact Analysis Request: Adding a Custom Reference Field on resource_allocation

[Arnaud5]

Hello ServiceNow Community,

I would like to gather feedback and best practices regarding a design decision in a Strategic Portfolio Management (SPM) / Resource Management implementation.

Context:

We currently have a reporting process based on the resource_allocation_daily table. The objective is to enrich allocation data with organizational hierarchy information (Service, Department, Division, etc.) and generate a consolidated reporting dataset.

- After analyzing the data model, we found that:

- resource_allocation_daily references resource_allocation through the allocation field.
- resource_allocation.group_resource references sys_user_group.
There is no native reference path between sys_user_group and cmn_department.
The current organizational mapping relies on a naming convention and an external mapping file, which we want to eliminate.

To address this, the proposed solution is to create a custom reference field:

1. Table: resource_allocation
2. Field: u_department
3. Type: Reference
4. Reference Table: cmn_department

This field would be automatically populated (Business Rule + Scheduled Job) based on existing business logic and then reused through dot-walking from resource_allocation_daily and downstream reporting processes.

Why we chose this approach

We intentionally decided not to extend sys_user_group, because it is a core platform table used by many applications (ITSM, HRSD, CSM, Approvals, etc.), and we consider that to be a higher-risk customization.

The alternative was therefore to add the custom field on resource_allocation, which is more specific to the PPM/SPM ecosystem.

Concern:

Although the technical solution seems straightforward, we are aware that resource_allocation is still a ServiceNow-delivered table shared by several applications such as:

Resource Management
Strategic Portfolio Management (SPM)
Agile Development
Project Portfolio Management (PPM)

Before moving forward, we would like to understand whether there are any architectural, upgrade, performance, or maintainability risks associated with extending resource_allocation with a custom reference field.

Questions:
1. Is adding a custom field on resource_allocation considered a supported and common practice in SPM implementations?
2. Have you experienced any issues during upgrades after extending this table?
3. Could there be any impact on Resource Management engine performance, Resource Plans, Capacity Planning, or Agile integrations?
4. Are there better alternatives that would avoid modifying resource_allocation while still providing a maintainable relationship between allocation data and cmn_department?
5. If you had to implement this requirement today, would you:
extend resource_allocation,
create a dedicated mapping table,
use a database view,
use a separate denormalized reporting table,
or choose another approach?

Any feedback from architects or customers who have customized resource_allocation in production SPM environments would be greatly appreciated.

Thank you in advance for your insights.

Arnaud