eptably by most common-value languages. Structure cannot, however, since it requires the identification of efficient architectural principles of the actual domain. As network systems are concerned, a few principles are common knowledge, e.g., separating access network problems from core network problems. Some new principles (e.g. the "layer" concept) were defined by the OSI model. Over the last two decades a number of new principles have emerged (e.g., the concepts of "horizontal net- works" and "logical networks"), which cannot be defined in terms of common knowledge and the OSI model. In AMLn, all essential architectural principles (old, useful ones and new ones) are built-in. The general principle applied for managing complex system is "sepa- ration of concerns." AMLn is based on two main concerns: Separating functionality from connectivity. These subjects are covered in Chaps. 2 and 3 respectively. Separate the system that offers services to system users (the ' managed or traffic system") from the system that manages that system (the "management system"). How these systems are related is described in Chap. 5, that also discusses exist- ing management systems (TMN, SNMP, CORBA and OMAP) through AMLn models. Preface Whenever you separate concerns, you must also define how to integrate the parts, since a system consists of related parts. Chapter 4 discusses this subject as regards the separation of functionality from connectivity. The chapter also consid- ers that the specification of a network system is always created by breaking down its structure step by step. The structure of an AMLn model that results from this is characterized as its network-level structure. Chapter 6 presents some case studies where AMLn has been applied as an anal- ysis tool on well known network systems. An overview of AMLn is given in Chap. 1. A brief introduction to modeling in general is also included, as well as the definition of the logical dimensions in which an AMLn model may be viewed. Logical dimensions are conceptual tools for