PACT: A Reference Viewpoint Taxonomy for Software-Intensive Systems

Architecture viewpoints play a central role as an abstraction mechanism for structuring, communicating, and reviewing software architectures by separating concerns and addressing diverse stakeholder needs [1] [8] [9] [11]. However, in both industrial practice and academic research, viewpoint definitions are often fragmented, inconsistently expressed, or narrowly scoped, which limits comparability, reuse, and long-term architectural evolution [10] [14] [15]. Existing architecture frameworks and standards, including TOGAF, C4, and ISO/IEC/IEEE 42010, either emphasize processes and notations or deliberately avoid prescribing concrete viewpoint sets [1] [4] [33]. While this flexibility supports broad applicability, it also leaves practitioners without a reusable reference taxonomy that systematically consolidates architectural concerns encountered in modern software-intensive systems [8] [10] [11]. This paper introduces PACT (Practical Architecture Viewpoint Taxonomy), a reference-level taxonomy of architecture viewpoints that consolidates recurring architectural concerns observed across standards, established viewpoint models, and industrial practice. PACT defines 52 viewpoints spanning business, application, integration, data, security, infrastructure, governance, and operations concerns. Each viewpoint is specified using a unified definition template that captures its primary concern, key questions, stakeholders, abstraction focus, and scope, enabling systematic comparison, selection, and reuse [1] [11]. PACT is explicitly aligned with the conceptual model of ISO/IEC/IEEE 42010, while remaining method-, notation-, and tool-independent, enabling reuse across heterogeneous architectural practices without imposing process or documentation lock-in [1]. It is intended as a reference taxonomy rather than a prescriptive framework, supporting enterprise architecture governance and system design practices [6] [7], as well as academic analysis of architectural knowledge and viewpoints [15] [18]. A case-based evaluation and industrial illustrations illustrate how PACT supports more systematic concern coverage, improved clarity, and structured architecture reviews across heterogeneous systems. The taxonomy is designed to be extensible, providing a stable reference for future research and evolving architectural practices [10] [32].