## 4 Application Features
### Mapping Real World Food Plans  
Before designing the interface, it was essential to understand what the system is to its users instead of how the designers present it. This was carried out by creating conceptual models, namely by the definition of a system metaphor [55]. The principles beneath this approach relate to the definition of analogies with the real world; the definition and relation between concepts correctly mapped to the task domain supported by the system. Therefore, in the context of the work presented in this paper, it was crucial to understand what meal planning is for users.  
Conceptually, meal planning includes types and amounts of food, incorporating dietary fiber, understanding proper serving sizes, management of eating out and special occasions, as well as incorporating favorite recipes. In real terms, meal planning relates to different food types in a dish. Meals are different throughout the day; the major understood types are breakfast, lunch, snack, and dinner. With this in mind, and considering knowledge acquired by users throughout their lives, a metaphor for the system is the Plate Model [56], as presented in Figure 2. It is a visual method of food representation through pictures, graphs, charts, and food replicas. The centerpiece is the dinner plate, which serves as a pie chart representing the proportions of food. The model also includes side dishes, beverages, and other meal courses. One of the critical elements in nutrition is learning appropriate food quantities. To this end, portion size is an essential aspect of the plate model. Each food must be visually represented in the correct size concerning the overall food distribution  
Figure 1: System architecture.  
on the plate. Using the plate model allows users to understand the concept and carry out tasks in an interface as in real life.  
The metaphor used in this context imposes two significant constraints: the creation of sections in the dish--where food is placed--and the visual representation of food so that users will understand the meal. For the first, as presented in Figure 3, the general idea is to create sections in the dish that contain food (considering the food plan prescribed by a nutritionist). The algorithm used to create the circular areas is presented in Section 4.2.1.  
For the visual representation of food products, a list of 1307 products was considered. Given the effort required to create each item, they were separated into 77 categories representing several food products or groups. Similar categories were grouped into contexts (presented in Table A1 of Appendix B): drinks, common carbohydrates, milk derivatives, deserts and sweet food, proteins, fruits, vegetables, and other categories that do not fit in the previous. All the elements were created in the scope of this paper for an accurate representation of the food products.  
Another important aspect is the percentage of food ingested from the dish. The real-time monitoring of a food plan depends on the feedback on the adequate ingestion of nutrients. It avoids misleading feedback on meal consumption. Therefore, it is critical to represent the percentage of consumed food, which is concordant with the common knowledge of users and the plate model, instead of looking at grams of consumption, which are much more challenging to measure. This way, visual markers were created, representing 200%, 150%, 100%, 75%, 50%, and 25% of each food in the prescribed meal, as shown in Table A2 of Appendix B.