RESUMEN
A team of health care stakeholders and researchers collaboratively developed a qualitative model and graphic representation of the continuum of HIV care in Vancouver to inform delivery of antiretroviral therapy and other HIV health services. The model describes the patient journey through the HIV care continuum, including states of infection, health services, and care decisions. We used a Unified Modelling Language (UML) activity diagram to capture patient and provider activities and to guide the construction of a UML state machine diagram. The state machine diagram captures model agent states in a formalism that facilitates the development of system dynamics or agent-based models. These quantitative models can be applied to optimizing the allocation of resources, and to evaluate potential strategies for improved patient care and system performance. The novel approach of combining UML diagrams we present provides a general method for modelling capacity ---management strategies within complex health systems.