The UDI Specifications are organized into multiple books, as described in detail in the "Document Organization" chapter of the UDI Core Specification. The UDI Core Specification contains the definitions for UDI services and facilities required in all UDI environment implementations. The other specification books represent independent, optional services which may be common but are not required in all implementations.
Bound copies of the Version 1.01 UDI Specifications are available from CerTek Software Designs, Inc. See http://www.certek-software.com/udi.html for details on ordering bound copies.
The UDI Specifications contain the only "normative" documentation (that is, the official definition of the interfaces). All the other documents are "informative": they provide useful information and background to help in understanding how to use and implement UDI environments and drivers. See here for informative documents from Project UDI.