Using Topic For Publish / Subscribe

I am using a Producer Tool which creates a Topic of Name "abcd" and i am
creating a message over this topic. When the Consumer gets connected and
subscribed to the topic "abcd" he will get the messages asynchronously. But
my requirement is when i re-run the Producer tool the previous topic is
overriddedn with the same topic name with the new message. I do not want
this to happen. Please suggest me any solution.