Call Open to set the Active property for the dataset to true. When Active is true, data can be populated with data. It can read data from a database or other source (such as a provider). Depending on the CanModify property, active datasets can post changes. 

Setting Active to true: 

Triggers the BeforeOpen event handler if one is defined for the dataset. 

Sets the dataset state to dsBrowse. 

Establishes a way to fetch data (typically by opening a cursor). 

Triggers the After Open event handler if one is defined for the dataset. 

If an error occurs during the dataset open, dataset state is set to dsInactive, and any cursor is closed. 

DataSource 

State 

AfterOpen 

BeforeOpen 

Close 

CanModify 

Opening and Closing Datasets 

Fetching the Data