## 2 Engineering Design Meta-Model for Interface Design
### Engineering Design Domains  
To systemize the engineering design knowledge for the inclusive design of a multimodal user interface, the concept of domains is used. A domain in engineering design interface refers to a specific aspect or area of the design problem. It encompasses different kinds of design activities and represents a distinct subset of knowledge. The world of design modeling of a multimodal user interface as a living product can be defined in four domains: (i) _user domain_, (ii) _function domain_, (iii) _physical domain_, and (iv) _process or task domain_. **User domain. ** In interface mobile phone design, user domain refers to the full range of user characteristics and needs that designers must consider when creating interfaces. This includes but is not limited to users' physical and cognitive abilities, cultural and linguistic backgrounds, technical skills, and goals and motivations related to using an interface on a mobile device. Overall, the user domain is a complex and multifaceted concept that requires designers to consider a wide range of user characteristics, needs, preferences, and desires in order to create interfaces that are inclusive, accessible, and engaging for all users. The user domain is characterized by attributes a user desires. With this viewpoint, an interface is seen for what it gives to the user, without or with knowledge about the interface of a mobile phone or how the interface, as a \"living product\", works. The user domain includes attributes related to convenience, accessibility, multilingual support, and accuracy. The user domain also includes factors such as user preferences, expectations, and context of use. For example, some users may prefer a minimalist interface, while others may want a more visually rich and stimulating interface. The context of use may also vary, which can affect the design of the interface to ensure usability and accessibility. In essence, the user domain represents the human-centered approach to design, which prioritizes the needs and desires of the user to create interfaces that are intuitive, efficient, and satisfying to use. **Function domain**. The function domain is broad and encompasses a wide range of technical and functional specifications that the interface must fulfill to ensure accessibility, usability, and effectiveness for all users. Essentially, functions represent abstractions of the interface's behavior. In the context of mobile phone interface design, the functional domain comprises the set of functional requirements from a design and engineering point of view that the interface must satisfy to provide a complete and satisfactory user experience to all users, including those with diverse needs and abilities. The functional domain is concerned with specifying the desired performances of the interface as a living product. It encompasses the various actions and interactions that the interface engages in with its users over its lifetime. These interactions are complex, dynamic, and multifaceted, and they define the functions of the interface. **Physical domain**. Designers and engineers need to imagine and define solutions in the physical domain to meet the functional requirements in the functional domain. The physical domain encompasses the physical components and structure of the interface as a living product, which are strategic elements in mobile development. It includes hardware components like the mobile device and software components such as the interface layout, typography, color, and visual design elements. The physical domain refers to the product's physical, tangible characteristics. The design of a product is studied in this domain. Interaction between the user and the interface is an important consideration in the physical domain, such as the configuration of the interface. Moreover, accessibility is also an essential aspect of the physical domain, including considerations like the size and color contrast of text and visual elements and support for assistive technologies.