Activation 
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 the 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.
ABAP programs and screens get the information they require about ABAP Dictionary objects from the runtime objects. Changes to ABAP Dictionary objects are determined by comparing the time stamps (see
Runtime Objects). Changes to ABAP Dictionary objects therefore 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.
After changing a domain, for example changing the data type or the length, all tables in which a field refers to this domain must be reactivated. This ensures that all these tables are adjusted to the changed technical field information.
Activating an object can therefore affect numerous dependent objects. Prior to activating a modified object, you should therefore find out what the effect of this action will be. You can display all the objects that are dependent on an object with the Where-used list 
in the maintenance screen of the object.
You can also 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 (for example, if a domain that is used in many tables is to be activated), you should choose
Activating Objects in the Background for the object.
