Segments in BDoc Types 
All the BDoc types contain a hierarchical structure that serves as a container of business data. These containers are different for messaging and synchronization BDoc types as explained below:
· mBDoc type contains:
¡ A hierarchical segment structure
The segment structure is not mapped to database tables. Therefore, mBDoc types do not contain any parameter information. The hierarchical segment structure may contain a selection of fields of the extension for receiver determination, which allows the filter criteria to be specified for these fields in replication modeling.
¡ An extension
The extension is the container of the actual business data. It is modeled in the ABAP Dictionary as a complex data structure.
· sBDoc type contains:
A segment structure that serves as the container of business data. All the segments of a sBDoc type can be mapped to more than one databasetable. Segments can be hierarchically dependent to handle parent and child records together.
See also: