0 Introduction.- 0.1 Key topics of open distributed systems design.- 0.2 The role of standards.- 0.3 The need for formal descriptions.- 0.4 Distributed systems from the point of view of DAI.- 1 Formal methods in the system design process.- 1.1 A model for the system design process.- 1.2 Requirements for formal description techniques.- 1.3 Synthesis and analysis activities.- 2 Requirement specification of open distributed systems.- 2.1 Basic architectural concepts.- 2.2 System architectures.- 2.3 Refinement and abstraction.- 2.4 The Basic Reference Model of Open Systems Interconnection.- 2.5 Basic concepts of formal description techniques.- 2.6 Some remarks.- 3 The design of a temporal logic for open distributed systems.- 3.1 Some requirements on expressiveness.- 3.2 A survey of temporal logics.- 3.3 A modular temporal logic for open distributed systems.- 4 The interaction point concept.- 4.1 The role of interaction points.- 4.2 A list of possible interaction point properties.- 4.3 Formal specification of interaction point properties.- 4.4 Formal reasoning about interaction points.- 4.5 Interaction point representations in operational FDTs.- 4.6 Conformance between abstraction levels via the interaction point concept.- 5 Communication services.- 5.1 The service concept.- 5.2 Design methodology.- 5.3 Example "modified InRes service".- 5.4 Conclusion.- 6 An epistemic logic for open distributed systems.- 6.1 The role of knowledge.- 6.2 Notions of knowledge.- 6.3 A modular epistemic logic for open distributed systems.- 7 Applying temporal epistemic logics to open distributed systems.- 7.1 Example "mutual exclusion".- 7.2 Example "drink server".- 8 Conclusion.- References.- A.1 Theorems and valid formulas.- A.2 Ordering properties for the service provider.- A.3Abbreviations.- A.4 Notation.