Bahmni EMR server consists of the OpenMRS core and all the omods packaged as part of the Bahmni distribution. We have few core omods(necessary to run OpenMRS) and others are mostly per feature. To understand the code structure of omod refer Creating OMODS. 

There are two ways of writing Web API :

• CRUD API: CRUD means the basic operations to be done to a domain object (Create, Read, Update, Delete). You directly handle records or objects; apart from these operations, the records are passive entities. 
  • Example: ConceptResource
• REST API: REST, on the other hand, operates on resource representations, each one identified by an URL. These are typically complex objects abstractions/operations.
  • Example: BahmniEncounterController. 

Based on the requirement/module convention we adopt one of the two above mentioned ways.

See Adding a CRUD API(*Resource.java) and Adding REST API(*Controller.java).