I collect a lot of configuration values from my database servers and most of these values are stored by date.
So often I end up with values such as:
config_date config_value
2010-09-01 value_1
2010-09-02 value_1
2010-09-03 value_2
2010-09-04 value_3
2010-09-05 value_3
2010-09-06 value_3
2010-09-07 value_3
2010-09-08 value_4
2010-09-09 value_4
2010-09-10 value_1
2010-09-11 value_5
2010-09-12 value_5
2010-09-13 value_5
config_from config_to config_value
2010-09-01 2010-09-02 value_1
2010-09-03 2010-09-03 value_2
2010-09-04 2010-09-07 …