  The Advanced Photon Source is now in its fifth year of routine beam
production. The EPICS-based [1] control system has entered the phase in its
life cycle where new control algorithms must be implemented under increasingly
stringent operational and reliability requirements. The sheer volume of the
control system (~270,000 records, ~145 VME-based input-output controllers
(IOCs), and ~7,000,000 lines of EPICS ASCII configuration code), presents a
daunting challenge for code maintenance.
  The present work describes a relational database that provides an integrated
view of the interacting components of the entire APS control system, including
the IOC low-level logic, the physical wiring documentation, and high-level
client applications. The database is extracted (booted) from the same
operational CVS repository as that used to load the active IOCs. It provides
site-wide decision support facilities to inspect and trace control flow and to
identify client (e.g., user interface) programs involved at any selected point
in the front-end logic. The relational database forms a basis for generalized
documentation of global control logic and its connection with both the physical
I/O and with external high-level applications.
