3.1.2. Application Modules
A module is the smallest structural part of a CUBA application. It is a single module of an application project and the corresponding JAR file with executable code.
Standard modules:
-  global – includes entity classes, service interfaces, and other classes common for all tiers. It is used in all application blocks. 
-  core – implements services and all other components of the middle tier. 
-  gui – contains components of the generic user interface. It is used in the Web Client block. 
-  web – the implementation of the generic user interface based on Vaadin. 
-  portal – an optional module – implementation of Web Portal based on Spring MVC. 
-  front – an optional module – implementation of Frontend User Interface in JavaScript. 
    Figure 7. Application Modules