I know that what we purchase on U.W. store shelves is only one version of ketchup, or catsup. In the Philippines, it's made from bananas, though I never had the chance to taste it.
It's like mole' sauce. We think of it as a sauce of Mexican, or South American origin that has chilis and unsweetened chocolate. And yet we eat guacamole. Mole' means sauce. Guaca is the avocado part. Guacmole is avocado sauce. Do a quick Google search and you will no doubt find a host of ketchup recipes. Good luck. I hope you find one you truly love. Or, take a look at several to get an idea of what ketchup is, then create your own recipe. That's what I'd do.
The following link gives a surprising history of ketchup, where it originated and interesting facts, as well as recipes: http://homecooking.about.com/od/food...huphistory.htm
Seeeeeeya; Goodweed of the North