A business object type is the representation of a business entity, like an employee or a sales order, in an SAP System. It encompasses both the functions (in the form of methods) and the data (in the form of attributes) of this entity. In the process, the implementation details of the business object type are hidden from the end user, and the business object type itself is accessed through defined functions (methods/BAPIs). This is referred to as encapsulation.

Business object types are used to break a SAP system down into smaller, disjunctive units. As a result, the system’s structure is improved while its complexity is reduced.

Business object types form the point of entry to the data and the functions of an SAP System. At business object type level, non-SAP systems can communicate with an SAP System, and the various SAP business components can communicate with each other.

To encapsulate the SAP data and business processes, SAP business objects are defined as entities with multiple layers, as illustrated in the following graphic:

• The innermost layer of the SAP business object is the kernel, and represents the object’s inherent data. It contains attributes like the name, age, or address of an employee.

• The second layer, the integrity layer, contains the business logic of the object. It comprises the business rules for consistent embedding in the environment and the constraints regarding the values and domains that apply to the business object types.
  

• The third layer, the interface layer, supplies the valid options for accessing the business object type, defining the object’s interface to the outside world. The methods/BAPIs for accessing the objects are housed here.
  

• The fourth and outermost layer of a business object is the access layer. It defines the technologies that allow external access to the object data.

As above diagram shows, the interface layer separates a business object type’s data from the applications and technologies that are used to access it. To the outside, business object types reveal only their interface, which consists of a set of clearly defined methods. Applications can only access the business object type data through the methods of that type.

An application program wanting to access an SAP business object type and its data only needs the information required to execute the methods. Therefore, application programmers can work with SAP business object types and call their methods without having to know anything about SAP-specific implementation details of the object.

The set of methods associated with a business object type represents the object’s behavior. When a method is executed on a business object type, the method can change the object’s internal state, that is, the object’s data.

For example, one method that you can use on business object Employee is to "check for the employee’s existence".

The term "business object type" corresponds to the term "class" in object-oriented programming languages. It defines a template for concrete objects that all have the same structure and the same behavior. For example, the individual employees working in an organization are all part of the Employee object type.

The object types are descriptions of actual SAP business objects that can exist in R/3; that is, each individual SAP business object is a representation, or instance, of its object type. For example, the employee with the name Charlie Jones and the employee number 1234 is an instance of the Employee object type.

When writing object-oriented application programs, developers identify the object types that are to be used in their programs. At runtime, the application program accesses the specific instances of the defined object types.