Anatomy of a transaction
The application transactions are accessed from the outside through servers. A server receives a request to perform a transaction. Since the request comes from another system, its data are specifically formatted. The server therefore uses formats to unformat the request data.
The server then invokes an operation. Operation is a sequence of operation steps. Each step may access and manipulate the data, request services or call other operations. When the operation requests a service, it formats the request data using a format and passes them to the service, performs the service and finally unformats received response data again.
After the operation completes, the server formats response data and replies them to the transaction originator.