AppML, as an application modeling language, comprises various fundamental components or elements that collectively describe the structure, behavior, and data of an application. The specific elements may vary depending on the implementation or version of AppML, but here are some common fundamental components:

Entities : Entities represent the fundamental building blocks of the application. They can denote real-world objects, concepts, or data structures within the application domain.

Attributes : Attributes describe the properties or characteristics of entities. These can include properties such as name, type, size, and any other relevant details specific to an entity.

Relationships : Relationships define connections or associations between entities. They describe how different entities are related to each other within the application model.

Actions/Behaviors : Actions or behaviors refer to the functionalities or operations that entities can perform. They describe what an entity can do or how it can be manipulated within the application.

Events : Events represent occurrences or triggers that initiate specific actions or behaviors within the application. They define when and how certain actions or processes are activated.
Constraints and Rules : Constraints and rules establish conditions, limitations, or guidelines within the application model. These constraints may define validation rules, business logic, or other restrictions that entities must adhere to.

Views/UI Elements : Views or user interface elements describe how entities and their attributes are presented to users. They encompass the visual representation and interaction elements of the application.

Hierarchy and Structure : AppML often includes elements to represent hierarchies or structural relationships between entities. This could involve grouping entities or defining parent-child relationships.

Metadata and Annotations : Metadata and annotations provide additional information or context about elements within the AppML model. These can include descriptions, tags, or other metadata to enhance understanding or provide documentation.

Modules/Components : AppML may support the modularization or componentization of the application, allowing the model to be divided into smaller, reusable parts.