Architecture of the UML

1. Metametamodel
   defines a language that specifies classes, use cases, components, and all other UML elements
   
2. Metamodel
   defines the language for specifying a model, less specific layer (Ex. node, class)
   
3. Model
   it is a layer in which you work with an expert or a client to get a handle on a domain, and a potential system users to understand the use cases that will go into making they system
   
4. User Objects
   most specific layer, where 'user' refers to a user of the UML (Ex. Component diagram of my home computer system)