The Functional Viewpoint provides an analysis of abstract functional elements and their logical interactions. This is in direct contrast to the physical and communications viewpoints that focus on engineering concerns of how functions are implemented, where they are allocated, how they transfer information, which protocols are used, and what method is used to implement them. In other words, the Functional talks about "the what" while the Physical and Communications are more concerned with "the how."
Stakeholders that take a project development role in an ITS deployment may be informed by the functional viewpoint, in particular the requirements, which are allocated to functional objects in the Physical View. Mostly, this would be stakeholders filling the role of Service Provider, Application Developer or Device Developer. The functional view can help these stakeholders answer questions such as:
- What kinds of data are required to implement a given service?
- What functionality is required to implement a given service?
The ARC-IT Functional Model is developed using a Structured Analysis methodology, based on the work of Hatley/Pirbhai. Previous versions of the National ITS Architecture depicted the logical architecture using Yourdon-Demarco Data Flow Diagrams; while the Functional Model does not include those graphics, it does use some of the same structural artifacts:
- Process: A function or activity that is required to support service package needs. A Process performs actions to achieve an objective or to support actions of another process. This may involve data collection, data transformation, data generation, data generation or processing in performing those actions. The most detailed processes (sometimes called primitives) are defined in Process Specifications (P-Specs).
- Process Specification (p-spec): The textual definition of the most detailed processes. The process specification includes an overview, a set of functional requirements, and a complete set of inputs and outputs.
- Data Flows: Representations of data flowing between processes or between a process and an external physical object (or terminator) in the functional view. Data flows are aggregated together to form high-level information flows in the physical view.
- Terminator: An external physical object that represents a system beyond the architecture boundary. A terminator may be a source and/or a sink for information. ARC-IT does not define any of the internal functionality of a terminator.
The Functional View defines Processes to control and manage system behavior, such as monitoring, and other active control elements that are part of describing the functional behavior of the system. The functional view presents processes in a top-down fashion beginning with general processes (e.g., "Manage Traffic") that are then decomposed into more detailed processes (e.g., "Provide Traffic Surveillance", "Monitor HOV Lane Use").