1. A data processing system including one or more data storage devices configured to store data accessed by an application program being executed by the data processing system, the data processing system comprising: a data structure organizing items stored in the one or more data storage devices, the data structure organizing information resident in a user database used by said application program, the data structure including: a primary user data structure for each user of the system configured to organize each data item associated with the user into one of four categories including: a Who data set configured to organize data items associated with who the user communicates with including contacts the user, a What data set configured to organize data items associated with what the user does including daily activities the user engages in, a Where data set configured to organize data items associated with locations including places of interest to the user, and a When data set configured to organize data items associated with when the user is doing something including calendar information for events of the user, wherein each data set identifies data items stored in a corresponding Who database, What database, Where database, and When database for system users; and one or more data processing devices configured to execute the application program and access the data structure to generate an interactive graphical user interface for presentation by a user device, the graphical user interface configured to present data items of the user organized thematically according to the four categories in a manner that is intuitive to the user.