I finished reading UIMA Ruta official documentation which is very helpful. I was wondering whether there is more material on UIMA Ruta to continue my reading (and learning). Could you suggest any other documentation/book/paper/website that you believe is relevant to this scripting language and maybe NLP from that particular view? Until now, I've found and read a paper titled UIMA Ruta: Rapid development of rule-based information extraction applications.
The official documentation is the main and most up-to-date source of information about UIMA Ruta.
The paper UIMA Ruta: Rapid development of rule-based information extraction applications provides an overview of the system with some additional information about teleated work and use cases. However, the paper refers to version 2.2.0 as far as I remember. The current version of UIMA Ruta is 2.6.0 meaning the paper is rather outdated concerning the features of the language and integration, e.g., maven. Besides that, it's a good start to read. There are some other papers, which are however subsumed by this one.
There are slides of the tutorial at GSCL 2013 which refer to UIMA Ruta 2.1.0.
DISCLAIMER: I am a developer of UIMA Ruta and wrote all the mentioned material.