Loren Mark Walker
The purpose of this paper is to discuss key and highly focused topics that must be accurately developed during the initial stages of a system development via Model Based Systems Engineering. The four key overall topics addressed are: Customer Needs, System Use Cases & Scenarios, Architecture/Modeling and Requirements. The initial stages refers to the upper left of the SE Vee diagram where it is essential to develop and understand Customer Needs and translate these into well-defined Use Cases, the initial Model Based Systems Engineering (MBSE) architecture Models/Views and the development of consistent and mapped requirements. Note that the first stage of the Vee diagram may occur prior to a development contract, typically developed by Systems Engineering Technical Assistants (SETAs). In most cases, the customer employs the support of SETAs to provide systems engineering and architecture/modeling expertise during this period. The objective is to develop a well-documented set of concept architecture views/models that represent the customer’s needs, which should include Use Cases, Scenarios and the supporting context architecture views (i.e. sequence diagrams, activity diagrams, initial block diagrams, parametric diagrams, etc.)
The primary emphasis of this paper is the critical importance of “System” (sometimes referred to as “Enterprise”) level Use Cases, their associated Scenarios, the models/architecture views and they essential interrelationships. In addition, capturing the Customer Needs, the Use Case and other architecture views in a comprehensive Operational Concept Document (e.g. Concept of Operations) written primarily by the customer with the systems engineer’s and architect’s support. The integration of the triad of Use Cases/Scenarios, architecture/models and requirements will be discussed in detail to address the interrelationships between these overall topics.
A fundamental premise of this paper is that capturing the customer needs and the initial development of the Systems Engineering and Models, with the top level of requirements, in a well written Concept Document is absolutely critical for the entire life cycle of the system development and its operation. With this information written substantially in the customer’s operational terminology and supported by various architecture views, provides the basis for all future stages of a development.
The intent is to minimize the risk of developing a system that misses the intended customers’ needs for specific operational capabilities. All of the system development stakeholders (i.e. system engineers, acquisition/program management, supporting personnel, operational personnel, technical engineers, software engineers/coders, etc.) need to have this operational understanding of the intended customer use, goals and objectives for the system. Without this fundamental Concept Document, developers will be lost in attempting to meet written requirements (i.e. interfaces, functionality, etc.) without the fundamental written operational needs and Model Based Systems Engineering architecture views/modes that drive consistent and mapped requirements.