There has been some confusion about the roles of PDC and BPO in Modularity as the roles might seem overlapping. This document will briefly explain the roles of both services and highlight the main differences.
Long story short:
From my understanding, this design has been already valid on the Modularity Infra wiki page: https://fedoraproject.org/wiki/Modularity/Architecture/Infra?rd=Modularity/Infra
PDC – Product Definition Centre
PDC is the primary database for module metadata such as:
It provides a REST API to access and manipulate this data.
A part of PDC is also a web UI that will not be used in Modularity.
BPO – Build Pipeline Overview
BPO is a single web UI that will watch over the whole pipeline. Its primary function is to show the build state of each module.
Users will be also able to browse module metadata such as:
BPO uses its own database as a cache only to make the UI faster. The database: