This document discusses different levels and types of decision support systems (DSS). It begins by explaining that DSS are designed to support semi-structured and unstructured decision making by providing analytical models and access to databases. It then describes different levels of DSS including unstructured DSS which provide support for decision making in ill-structured situations. The document also covers capabilities and components of DSS, as well as how they can be developed and classified. It discusses group decision support systems and executive information systems.