UOHF Definition 2.1: Unified Ontology of Human Function

This publication presents UOHF Definition 2.1, the current authoritative conceptual definition and ontology architecture of the Unified Ontology of Human Function. Definition 2.1 retains the task-centered operational achievements of Definition 2.0 while correcting and expanding the scope of human function beyond real-world tasks alone. The human body is continuously engaged not only by external behavior, environment, and life tasks, but also by internal requirements for physiological maintenance, regulation, development, defense, adaptation, repair, and recovery. The formal definition is: Human function is the body's capacity to be appropriately engaged to meet internal and external demands. The corresponding Chinese philosophical definition is: 人体功能=身体被正常调用的能力。 In this definition, Demand includes ongoing internal requirements for physiological maintenance, regulation, development, defense, adaptation, repair, and recovery, as well as external behavioral, environmental, and real-world task demands. Definition 2.1 therefore establishes Demand, rather than Task alone, as the broader condition under which human function must be understood. A Task remains an important type of external activity or context, but a task is not identical to the demand it generates. The same task may produce different demands depending on load, duration, speed, environment, complexity, consequence, role, individual condition, and time. Internal physiological demands may also arise without any visible external task, including during sleep, rest, infection, injury, growth, adaptation, repair, or recovery. Definition 2.1 distinguishes: Demand, the internal or external requirement condition; Demand Specification, the versioned informational description of that demand; Task, a goal-directed activity or activity context; Task Demand, the external requirements generated by a task under specified conditions; Task Demand Specification, the versioned representation of those requirements; Engagement Requirement, what must be organized to meet the demand; Required Engagement Process Type, the expected process type capable of satisfying that requirement; Actual Engagement Process, the organization that actually occurs in the person; Actual Engagement Inference, the evidence-bounded conclusion about that process; Actual Engagement Representation, the versioned record of the inference. These entities are related but are not identical. Definition 2.1 generalizes Functional Engagement from a task-centered concept to a demand-centered concept. Functional engagement is the organization through which the body responds to an internal or external demand. Depending on scale and context, it may include molecular and cellular processes, tissue and organ processes, interactions among organ systems, structural support, functional capacities, sensory feedback, motor control, energy supply, metabolic regulation, protection, defense, adaptation, repair, recovery, cognition, behavior, and interaction with environmental conditions. Functional engagement does not mean conscious command, voluntary participation, patient engagement, service engagement, isolated neural activation, or one muscle contraction. It refers to the organized operation of the relevant human functions under a specified demand. The formal human-function definition includes the phrase appropriately engaged because the required functions must not merely operate. They must operate in a manner appropriate to the current demand, the person’s conditions, the available evidence, and the relevant safety and sustainability boundaries. At a general level, appropriate engagement requires that: the demand is sufficiently met; the organization remains sufficiently stable and adaptable; the associated cost and regulatory burden remain within sustainable boundaries appropriate to the context, time, and demand. Safety boundaries remain an independent constraint layer. Definition 2.1 also distinguishes the reality of human function from the evidence and representations used to describe it. Human function is not identical to human-function state.Demand is not identical to Demand Specification.Actual Engagement Process is not identical to Actual Engagement Inference.Actual response is not identical to manifestation or measurement result.Immediate cost is not identical to accumulated burden.Boundary is not identical to reserve.State is not identical to StateActual Inference or State Representation.Actual change is not identical to feedback information. This reality–evidence–inference–representation separation is essential for auditable reasoning, uncertainty management, provenance, version governance, and safe artificial intelligence. Definition 2.1 organizes UOHF into four connected components: UOHF — the governed ontology and semantic-rule foundation; the Human Function Engine — the bounded inference, state-convergence, action-control, and write-back layer; the Individual Human Function Model — the person-specific longitudinal representation of human-function state; the Human Function World Model — the temporal, multiscale, and action-conditioned modeling of human-function change. The development direction can be summarized as: Governed ontology topology → Human Function Engine → Individual longitudinal model → Human Function World Model The final scope of the Human Function World Model includes molecules, cells, tissues, bodily structures, organs, organ systems, physiological processes, cross-organ interactions, clinical mechanisms, disease, functional capacities, functional engagement, behavior, tasks, life contexts, and environment. These must be connected through state, cost, boundary, time, feedback, events, and change. Definition 2.1 does not treat local biological function as synonymous with whole-person human function. Molecular, cellular, tissue, organ, and system functions form the mechanisms, foundations, or limiting conditions through which whole-person human function is realized. UOHF must connect these scales without collapsing them into one ontological level. The framework also provides a unified interpretation of medicine, rehabilitation, and exercise: functional capacity → restoration of appropriate engagement → maintenance and enhancement of human function and expansion of engagement boundaries Medicine primarily addresses functional capacities, their biological foundations, disease mechanisms, and safety boundaries. Rehabilitation primarily addresses the return of functional capacities to real-world tasks and the restoration of appropriate engagement. Exercise maintains and enhances human function and expands engagement boundaries through sustained, appropriately dosed, and progressive engagement. Psychology and nutrition enter according to the current primary limiting factor, evidence, and professional scope. These are principal objectives rather than absolute professional boundaries. The current operational implementation remains strongest in task-centered assessment, state convergence, governed action, execution feedback, reassessment, and longitudinal service workflows. Definition 2.1 does not claim that internal-demand operationalization, complete multiscale mappings, a universal physiological-state classification, full OWL axiomatization, external expert consensus, clinical outcome validation, or a molecular-to-person simulator have already been completed. UOHF Definition 2.1 is therefore both a scope correction and an architectural clarification. It preserves the practical task-centered framework of Definition 2.0 while establishing the broader ontological foundation required to represent the body as a continuously regulated whole under internal and external demands.