Similarity and Granulation.- Mereology and Rough Mereology. Rough Mereological Granulation.- Learning data Classification. Classifiers in General and in Decision Systems.- Methodologies for Granular Reflections.- Covering Strategies.- Layered Granulation.- Naive Bayes Classifier on Granular Reflections.- The Case of Concept-Dependent Granulation.- Granular Computing in the Problem of Missing Values.- Granular Classifiers Based on Weak Rough Inclusions.- Effects of Granulation on Entropy and Noise in Data. - Conclusions.- Appendix. Data Characteristics Bearing on Classification.