What is RRDG and how does it relate to RPE?
RRDG stands for Rational Reporting for Document Generation. This is the document generation solution used by Rational tools that want to provide document generation capabilities from their own UI. RRDG does not provide a UI, it is the consumer products that provide that.
Current consumers of RRDG are IBM Rational DOORS 9.3, IBM Focal Point 6.4 and 6.5, IBM Rational Requirements Composer 2.x
RPE stands for Rational Publishing Engine. It is a standalone product, a document generation tool capable to consume data from Rational and select 3rd party products. It is built on top of RRDG. In addition to document generation capabilities, RPE includes visual tools to create templates and perform document generation as well as Web Services to support remote document generation. With RPE 1.1.2 a service for monitoring the document generation processes organisation wide has been added.
RRDG has been initially the core of RPE but in order to improve its consumption by Rational products and better manage requirements, both internal and external, it has spawned as a separate component from RPE.