Systems engineering focuses on developing a high-quality overall product. Usability engineering, on the other hand, aims to enable users to complete their tasks efficiently and effectively. Despite and because of their different focuses, both principles should find their place in the development process of a new product. This article will examine both disciplines in more detail and explain the most important steps in each development process. This will ultimately help us better understand how these processes can interrelate, and when they should occur.
With Systems engineering to the finished product
Objectives of Systems Engineering
Systems engineering pursues the goal of developing a high-quality product that is tailored to the user and customer needs with the greatest possible efficiency and effectiveness. To this end, requirements (e.g., economic and technical) covering the entire product life cycle are defined and documented as early as possible in the development process. These requirements culminate in a system design with subsystems. The process concludes with system validation. IEC 60601-1 proposes the V-model for this approach.
The development of a (medical) product proceeds in several consecutive phases. Annex H of IEC 60601-1 proposes a model for the PEMS development cycle for the development process. The special feature of this model is that the relevant tests are already specified during the planning and design phases. The descending branch of the V-model is processed first (from top to bottom). It deals with the gradual decomposition of requirements and risk analysis. It includes the capture of PEMS requirements, from which the PEMS architecture is derived. This is followed by the development of subsystems, the development of components, and finally the integration. The ascending branch of the V-model is processed from bottom to top. It includes PEMS integration, verification, and risk control.
Looking more closely, the first step is to define the Stakeholder requirementsHere, requirement engineers define and list requirements that must be implemented to satisfy various stakeholders. These stakeholders include, among others, legislators, purchasing decision-makers, operators, and users of the device. A complete list of stakeholder requirements includes requirements from the sub-areas of usage, market, technical, organizational, legal, and investor requirements.
In the next step, usability engineers will use the stakeholder requirements to PEMS specification with a definition of the interfaces between the subsystems.
The actual developers then take over this system specification in order to System requirements to define in order to develop a satisfactory product.
The subsystems are then defined and specified. Requirements for individual components are established.
Implementation and execution form the pinnacle of the V. In the integration phase, the individual components and systems are tested and validated one after the other, and risk management is verified.
Usability Engineering
Objectives of usability engineering:
By applying usability principles, the product should fulfill tasks with effectiveness, efficiency, satisfaction, and safety. The focus here is on the execution of tasks and subtasks and the user's interaction with the user interface. Key interaction principles according to ISO 9241-110 are task appropriateness, self-descriptiveness, conformity to expectations, learnability, controllability, robustness against user errors, and user retention.
According to IEC 62366-1, the creation of a usability file includes the implementation or creation of a Usage specification, one use-related risk analysis, one User Interface Specification and their verification, one formative evaluation and a final summative evaluation to.
The Usage specification Contains basic information on usage and the context of use. This includes the medical indication (intended purpose), the intended patient group, the user profiles (user groups and their typical work tasks), the usage environment, and the functional principle.
The use-related risk analysis analyzes user tasks in the context of the device and identifies usage errors (use scenarios). These errors cause hazards, hazardous situations, and risks. Potential damage and its severity are determined, and hazard-related usage scenarios are selected for the subsequent summative evaluation.
This is followed by the User Interface Specification. It essentially contains verifiable technical requirements of the user interface, design rules, as well as requirements regarding the parts of the UI that were identified in the use-related risk analysis. In the associated verification The usability engineer checks whether the specified requirements have been implemented.
The formative evaluation represents an evaluation accompanying the development process. For example, in the form of a “cognitive walk-through,” usage problems and errors are identified, and deficiencies and strengths of the user interface are identified.
The summative evaluation This is the final evaluation of usability and serves as proof that the user interface can be used safely. It is conducted with representative users in a representative usage environment.
So how does this fit together?
Now let's move on to the integration of the two disciplines. As previously described, the V-model lists the requirements and specifications on the left, and the corresponding tests and validations on the right. Before defining the PEMS system requirements, the requirement engineers work on the stakeholder requirements, and the usability engineers work on a system specification from a black-box perspective.
In the phase of developing the Stakeholder requirements (at systems engineering level) should simultaneously Surveys with potential users are conducted to derive user requirements. The questions relate to the users' tasks, their work results (including their quality), potential sources of error in task processing, and the individual sub-steps of the tasks. The goal in this stage is to derive user requirements and identify the product's core tasks in order to capture them in the stakeholder requirements. Each sub-task is captured in a user requirement. This allows the product to be precisely tailored to the end user.
During the PEMS specification should be within the framework of use-related risk analysis Core tasks are described and usage scenarios are designed. This includes analyzing tasks that are to be performed with the device to identify usage errors. By knowing the usage scenarios, a sequence of user actions on the device can be specified (abstraction level "enter", "select") and the subsequent reaction of the user interface (e.g., "display", "signal"). This often leads to new usage and system requirements that were not previously considered. In the next step, usage requirements described by "recognition" or "overview" can be converted into usage objects, and those containing "selection" or "setting" can be converted into tools. From this, the operating function and the user interface can then be fully specified. (User Interface Specification & Verification) are in the selection of control elements, a navigation structure, positioning of controls and design of (error) messages. A first prototype is now being designed for an interim evaluation (first formative evaluation) takes place in order to ensure that the device is also tailored to fulfil the important tasks in the further development process.
As part of the implementation the user interface is also being developed.
During the Component tests and during the PESS system test, the user interface and its components can be repeatedly subjected to formative evaluation to further improve the interface. Representative users may also be used for this purpose. With the PEMS system tests The usability should then be finally verified and the formative evaluation should thus be completed.
In the phase of PEMS validation the usability is determined in the form of summative evaluation be finally validated.
As you can see, systems engineering and usability engineering go hand in hand. And ultimately, good usability is an essential component for product success.
Best regards,
Katharina Rostan