Activation
When tables, types (data elements, structures, table types) and views are activated, they are placed at the disposal of the runtime environment in the form of runtime objects. These runtime objects contain information about the object in a form that is optimal for access by ABAP programs and screens. The runtime objects are buffered so that ABAP programs and screens can access the information relevant to them quickly.
The information about a table is divided amongst domains, data elements, field definitions, and the table definitions in the ABAP Dictionary. The runtime object of the table contains this information in an optimized form. You can see the function of the runtime object in the following figure.
ABAP programs and screens get the required information about ABAP Dictionary objects from the runtime objects.
Changes to ABAP Dictionary objects are determined by comparing the time stamps (for more information, see Runtime Objects ).Changes to ABAP Dictionary objects become effective in all system components when the objects are activated.
When an object is activated, all the objects dependent on it are also reactivated.
You change the data type or the length of a domain. After such a change, you must reactivate all tables in which a field refers to this domain. This ensures that all these tables are adjusted to the changed technical field information. The following figure presents a domain that is used in five different tables. All these tables must be reactivated.
Activating an object can affect numerous dependent objects. Before you activate a modified object, you have to find out the effect of this action. To display all the objects that are dependent on an object, choose 
with the quick info text Where-Used List on the maintenance screen of the object.
You can activate a large number of objects simultaneously using the mass activation program .
If a long runtime is expected in an activation because of a large number of dependent objects, you must choose Activating Objects in the Background for the object. Such a long runtime is expected, for example, when a domain that is used in many tables is to be activated.