A thought in the back of my mind made me go to the bookshelf, and voila:
"Koomen and Pol (1998) provide a model for test process improvement (TPI), which is particularly useful for structuring test processes. The TPI-model is an objective means to gain quick insight in the current situation of a test process. The model helps improvement in the form of key areas, maturity levels and improvement suggestions. It supports the definition of small and controlled improvement steps, baed on priorities." (Martin Pol, Erik van Veenendaal: Structured testing of information systems. An introduction to TMap, 1998, page 134).
To make the origins of this concept definitely clear - here's a footnote I found at www.polteq.nl:
"TMapŪ and TPIŪ are registered trademarks of Sogeti Nederland B.V. in the Netherlands. Martin Pol was the former manager R&D of Sogeti Software Control and responsible for the development of both the TMap approach and the TPI model."