Style-Based Reconfigurations of Software Architectures with QoS Constraints

We present Architectural Design Rewriting (ADR), a graphbased approach to deal with the design of reconfigurable software architectures. The key features we promote are: (i) hierarchical design; (ii) soft constraints for modeling QoS attributes; (iii) style-preserving reconfigurations; (iv) rule-based approach; and (v) algebraic presentation. Roughly, actual architectures are modeled by graphs with port and attribute nodes through which component edges are connected. Uniformly, QoS constraints on attributes are also modeled as edges. Architectures are designed hierarchically by a set of edge replacement rules that fix the architectural style. Depending on their reading, productions allow: (i) top-down design by refinement, (ii) bottom-up typing, and (iii) algebraic composition of typed architectures, with terms corresponding to style proofs. Moreover, productions exploit constraint primitives that can be used in the refinement phase, e.g., to reserve a certain amount of resources or to postpone architectural decisions. Similarly, reconfigurations are modeled as graph transformations triggered by constraints primitives to guarantee that certain levels of QoS are mantained. The main contribution is showing that we can take advantage by exploiting styles when specifying reconfigurations: (i) by giving hierarchical specifications that exploit the classes introduced by the style, (ii) by guaranteeing that all reconfigurations are style-preserving, (iii) by expressing reconfigurations as ordinary term rewrite rules on the algebra of style proofs. Overall, this results in a simple and formal mechanism for designing architectures according to a style, for checking that an architecture is an instance of a style and for ensuring style preservation during reconfigurations.