MARv-POS is a part-of-speech tagger tool (probabilistic POS annotation module). MARv4's architecture comprehends two submodules: a set of linguistically-oriented disambiguation rules module and a probabilistic disambiguation module. The linguistic-oriented is no longer used in the STRING chain because that function is now implemented by the RuDriCo module. MARv4 is based in Hidden Markovian Models using the Viterbi algorithm. The language model is based on second-order (trigram) models, which codify contextual information concerning entities, and unigrams, which codify lexical information.