Assessing architectural patterns trade-offs using moment-based pattern taxonomies

Large software systems are designed to satisfy or accommodate many requirements; architectural patterns are a well-known technique to reuse design knowledge. However, requested quality attributes (QA) may be inconsistent at times; e.g., high security typically hampers performance and scalability. Thus, a key concern of systems architects is understanding trade-offs among alternative solutions; e.g., a pattern may favor performance at the expense of scalability or security, another may privilege scalability, and yet another may push security. This article argues that the usual organization of individual patterns in topic-related pattern languages is not too helpful to identify trade-offs, and proposes to borrow a taxonomic principle of architectural tactics, organizing the patterns for each QA into 'moments'. This enables architects to use simple tradeoff highlighting techniques to understand trade-offs in complex systems. The approach was used in the systematic design of a SCADA-to-ERP secure bridge, where moment-oriented pattern taxonomies for availability, confidentiality, and performance were used. This approach offers the promise of enabling the trade-offenabled, pattern-driven design of large systems by supporting the systematic exploration of trade-offs among patterns for specific QA's.