I want to develop a bar chart with the following requirements:

An activity is represented as a box / rectangle with different colors. The colours change according to the activity. The width of the box determines the duration of the activity and is linked to start date and end date in a database record. The order of the activities will be changed by dragging the boxes (in the same row) and the record should be updated automatically. There are many people who are assigned these activities, which are represented in different rows. I should also be able to drag the boxes from one row to another with an immediate update of database.

Could anyone help in telling me the best approach for this task? I am just an intermediate programmer. I hope that my requirement is understandable. Please help me... :(