Data Objects
A data object is a part of the repository whose content can be addressed and interpreted by the program. All data objects must be declared in the ABAP program and are not persistent, meaning that they only exist while the program is being executed. Before you can process persistent data (such as data from a database table or from a sequential file), you must read it into data objects first. Conversely, if you want to retain the contents of a data object beyond the end of the program, you must save it in a persistent form.
Declaring Data Objects
Apart from the interface parameters of procedures, you declare all of the data objects in an ABAP program or procedure in its declaration part. These declarative statements establish the data type of the object, along with any missing technical attributes. This takes place before the program is actually executed. The technical attributes can then be queried while the program is running .
The interface parameters of procedures are generated as local data objects, but only when the procedure is actually called. You can define the technical attributes of the interface parameters in the procedure itself. If you do not, they adopt the attributes of the parameters from which they receive their values.
ABAP contains the following kinds of data objects:
Literals are not created by declarative statements. Instead, they exist in the program source code. Like all data objects, they have fixed technical attributes (field length, number of decimal places, data type), but no name. They are therefore referred to as unnamed data objects.
Data objects that have a name that you can use to address the ABAP program are known as named objects. These can be objects of various types, including text symbols, variables and constants.
Text symbols are pointers to texts in the text pool of the ABAP program. When the program starts, the corresponding data objects are generated from the texts stored in the text pool. They can be addressed using the name of the text symbol.
Variables are data objects whose contents can be changed using ABAP statements. You declare variables using the DATA, CLASS-DATA, STATICS, PARAMETERS, SELECT-OPTIONS, and RANGESstatements.
Constants are data objects whose contents cannot be changed. You declare constants using the CONSTANTSstatement.
Data objects that cannot be addressed using a name are known as anonymous data objects. They are created using the CREATE DATA statement and can be addressed using reference variables.
System-defined data objects do not have to be declared explicitly - they are always available at runtime.
Interface work areas are special variables that serve as interfaces between programs, screens, and logical databases. You declare interface work areas using the TABLES and NODESstatements.