Personalization keys allow the mobile user to define (personalize) certain input field values within the mobile application, by associating a name (key) with a  simple or complex datatype value.
 Mobile development supports two types of personalization keys:
-  User-defined  – you can define these when developing a mobile business object.  Before using these keys in a device application, each user sets their  own values. For example; name, address, zip code, currency, location, customer list, and so on.
 
- System defined (username/password) – refers to the user's  login credentials  used to  access enterprise information system (EIS) data. Unlike preference attributes, username/password is read-only and reset each time the user logs in or changes their password. The values are  typically used as personalization attributes or other data source runtime credentials.  The username/password system personalization keys do not support NULL values.