This paper is really the first instance of this idea:
D. McKelvie, C. Brew, and H. Thompson. Using SGML as a Basis for Data-Intensive NLP. In Proceedings of the fifth Conference on Applied Natural Language Processing (ANLP-97) 1997
Here's that article: anlp97.pdf
The pipes are "fat" because they pass XML between components.
Definition: A pipeline is a chaining of XML-in-XML-out components.
Note: The chaining doesn't have to be a simple "line" components strung output-to-input.