This Book presents a framework to enhance the retrieval, ranking, and categorization of text documents in medical domain. The contributions of this study are the introduction of a similarity model to retrieve and rank medical text-documents and the introduction of rule-based categorization method based on lexical syntactic patterns features. The first part introduces a method to formulate a similarity model by combining three features to model the relationship among document and construct a document network. While the second one introduces ROLEX-SP; a framework for automatically inducing rules to build text classifiers based on lexical syntactic patterns as a set of features to categorize text-documents. This Book is useful for people who are intended to build computer programs that extract new information from existing ones. The Book also provides algorithms for constructing and inducing knowledge among medical concepts and text.