how to define time dimension in flexfields

 Hi

I have a scenario where I want to define 4 desc flex field segments to replicate the time data entries in a contract. The 4 segments are:

1) Start Date

2) End Date

3) Duration

4) Period

I want the start date and end date to automatically calculate the duration and period. So for eg., if anybody enters start date as 19-Apr-2011 and End Date as 18-Apr-2012, the duration should automatically become 1 and the period "Year". Similarly, if somebody enters the start date as 19-Apr-2011, duration as 1 and period as "Year", the end date should automatically become 18-Apr-2012. Is this possible to implement in a flex field