Towards a Systems Engineering Pattern Language: Applying i* to Model Requirements-Architecture Patterns

This paper reports the results of exploratory research to develop a pilot pattern language for systems engineers at BAE SYSTEMS. The pattern language was designed to encapsulate knowledge about possible trade-offs made by systems engineers about architecture designs that satisfied different system requirements for submarine manoeuvring systems. Our intention is that this knowledge can be reused in future systems engineering processes using our ART-SCENE environment. Knowledge about requirements, design alternatives and the complex trade-off space was elicited from systems engineers. To model this knowledge we applied the i* formalism to represent the design space and design trade-offs, and to communicate the resulting patterns back to the engineers for validation and improvement. The research was a success, in that we produced a pattern language of 4 key patterns and their interactions for a submarine manoeuvring system, all using the i* formalism. The paper ends with a review of this research and how we plan to exploit the language to inform scenario-driven trade-offs between requirements satisfaction and architecture choice using the ART-SCENE environment. There is increasing recognition of the need for systems engineers to link system requirements and architecture designs. Considerable research is being undertaken into a range of topics – from tracing architectural decisions to requirements to relating architectural patterns to requirements patterns (Jackson 1995) and formal foundations of the requirements-architecture relationship (Hall et al. 2002). However this research tends not to investigate the systems engineering processes that its results are intended to support. Rather we argue that requirements-architecture research must be based on sound process models of concurrent requirements-architecture engineering. Using one such process model, this paper presents a novel pattern-based approach for exploring requirements-architecture trade-offs, and introduces an innovative pattern language that underpins such trade-offs. Our ART-SCENE (A nalysing R equirements T rade-offs – Scen ario E valuations) approach advocates a process in which systems engineers and stakeholders concurrently: 1. Generate and walk through system-level scenarios using our established CREWS-SAVRE process and software tools (Sutcliffe et al. 1998); 2. Acquire stakeholder requirements using the ACRE framework (Maiden & Rugg 1996) and model them using the i* formalism (Chung et al. 2000) with our REDEPEND tool (Maiden et al. 2002); 3. Model candidate system architectures using object-oriented modelling techniques supported by the AUTOFOCUS software tool (Huber et al. 1998); 4. Trade-off the satisfaction of different requirements by different architecture designs using scenarios to link requirements and architectures, then to simulate …