A transaction in SAP terminology is the execution of a program. The normal way of executing ABAP code in the SAP system is by entering a transaction code (for instance, SE51 is the code for the ABAP workbench). Transactions can be accessed via system-defined or user-specific, role-based menus. They can also be started by entering their transaction code (a mnemonic name of up to 20 characters) in the special command field, which is present in every SAP screen. Transactions can also be invoked programmatically by means of the ABAP statements CALL TRANSACTION and LEAVE TO TRANSACTION. Transaction codes can also be linked to screen elements or menu entries. Selecting such an element will start the transaction. The term "transaction" must not be misunderstood here: in the context just described, a transaction simply means calling and executing an ABAP program. In application programming, "transaction" often refers to an indivisible operation on data, which is either committed as a whole or undone (rolled back) as a whole. This concept exists in SAP but is there called a LUW (Logical Unit of Work). In the course of one transaction (program execution), there can be different LUWs.
Let’s have a look at the different kind of transactions:
1) Dialog transaction
These are the most common kind of transactions. The transaction code of a dialog transaction is linked to a Dynpro of an ABAP program. When the transaction is called, the respective program is loaded and the Dynpro is called. Therefore, a dialog transaction calls a Dynpro sequence rather than a program. Only during the execution of the Dynpro flow logic are the dialog modules of the ABAP program itself are called. The program flow can differ from execution to execution. You can even assign different dialog transaction codes to one program.
2) Parameter transaction
In the definition of a parameter transaction code, a dialog transaction is linked with parameters. When you call a parameter transaction, the input fields of the initial Dynpro screen of the dialog transaction are filled with parameters. The display of the initial screen can be inhibited by specifying all mandatory input fields as parameters of the transaction.
3) Variant transaction
In the definition of a variant transaction code, a dialog transaction is linked with a transaction variant. When a variant transaction is accessed, the dialog transaction is called and executed with the transaction variant. In transaction variants, you can assign default values to the input fields on several Dynpro screens in a transaction, change the attributes of screen elements, and hide entire screens. Transaction variants are maintained in transaction SHD0.
4) Report transaction
A report transaction is the transaction code wrapping for starting the reporting process. The transaction code of a report transaction must be linked with the selection screen of an executable program. When you execute a report transaction, the runtime environment internally executes the ABAP statement SUBMIT—more to come on that.
5) OO transaction
A new kind of transaction as of release 6.10. The transaction code of an OO transaction is linked with a method of a local or global class. When the transaction is called, the corresponding program is loaded, for instance methods an object of the class is generated and the method is executed.