In complex systems, it is difficult to identify which system element is involved in which requirement.

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Arranging the distribution of data, objects or components is a critical task that can ultimately affect the performance, integrity and reliability of distributed system. This paper suggests to write down what must (not) be available where in order to reveal conflicting distribution requirements and to detect problems early on. Distribution requirements are expressed via a new notion of constraints: a context-based constraint (CoCon) can indirectly select its constrained elements according to their context. The context of an element characterizes the situation in which this element resides and is annotated via metadata. CoCons facilitate checking the compliance of a system or a model with distribution requirements during (re-)design, during (re-)configuration or at runtime. This paper focuses on validating UML models for compliance with distribution CoCons in order to take distribution requirements into account right from start of the development process.

Software evolution is a major challenge to software development. When adapting a system model to new, altered or deleted requirements, existing requirements should not unintentionally be violated. One requirement can affect several possibly unassociated elements of a system. A new constraint technique is introduced in this paper: One context-based constraint (CoCon) specifies a requirement for those system (model) elements that belong to the related context. The constrained elements are indirectly selected via their meta-information. Thus, verifying compliance with requirements can be supported automatically when a system's model is modified, during (re-)configuration and at runtime. 1 Introduction: Continuous Engineering 1.1 Continuous Engineering Requires 'Design for Change' The context for which a software system was designed changes continuously throughout its lifetime. Continuous software engineering (CSE) is a paradigm discussed in [18] for keeping track of the ongoing changes and to adapt legacy systems to altered requirements as addressed in the KONTENG 1 project. The system must be prepared for adding, removing or changing requirements. The examples in this paper concentrate on component-based software systems because this rearrangeable software architecture is best suited for CSE. New methods and techniques are required to ensure consistent modification steps in order to safely transform the system from one state of evolution to the next without unintentional violating existing dependencies or invariants. This paper focuses on recording requirements via constraints in order to protect them from unwanted modifications. However, an enhanced notion of 'constraint', introduced in section 3, is needed for this approach. 1.2 Focus: Requirements Specification in System Models This paper proposes to express important requirements via a new specification technique that facilitates their consideration in different levels of the software

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