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Shared understanding is essential for efficient communication in software development and evolution projects when the risk of unsatisfactory outcome and rework of project results shall be low. Today, however, shared understanding is used mostly in an unreflected, intuitive way. This is particularly true for implicit shared understanding. In this paper, we investigate the role, value and usage of shared understanding in Software Engineering. We contribute a reflected analysis of the problem, in particular of how to rely on implicit shared understanding. We discuss enablers and obstacles, compile existing practices for dealing with shared understanding, and present a roadmap for improving knowledge and practice in this area.

Survivability is receiving increasing attention as a key property of critical systems. Survivability is the capability of a system to fulfill its mission, in a timely manner, in the presence of attacks, failures, or accidents. We present a method for analyzing survivability of distributed network systems and an example of its application. Survivability requires system capabilities for intrusion resistance, recognition, and recovery. The Survivable Network Analysis (SNA) method permits assessment of survivability at the architecture level. Steps in the method include system mission and architecture definition, essential capability definition, compromisable capability definition, and survivability analysis of architectural softspots that are both essential and compromisable. Intrusion scenarios play a key role in the analysis. SNA results are summarized in a Survivability Map that links recommended survivability strategies to the system architecture. The case study summarizes application of the SNA method to a subsystem of a large-scale, distributed healthcare system.

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Pervasivesocietal dependency on large-scale, unbounded network systems, the substantial risks of such dependency, and the growing sophistication of system intruders, have focused increased attention on how to ensure network system survivability. Survivability is the capacity of a system to provide essential services even after successful intrusion and compromise, and to recover full services in a timely manner. Requirements for survivable systems must include definitions of essential and non-essential services, plus definitions of new survivability services for intrusion resistance, recognition, and recovery. Survivable system requirements must also specify both legitimate and intruder usage scenarios, and survivability practices for system development, operation, and evolution. This paper defines a framework for survivable systems requirements definition and discusses requirements for several emerging survivability strategies. Survivability must be designed into network systems, beginning with effective survivability requirements analysis and definition.

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