Place ribs in a large stock pot, and cover with water. Bring to a boil, and cook for 15 minutes. In a mixing bowl, mix together ketchup, onion, garlic, brown sugar, Worcestershire sauce, and soy sauce. Remove ribs from water, and transfer to a slow cooker. Pour sauce over ribs. Cover, and cook on low for 6-8 hours, or until ribs are tender. If sauce is too thin when cooking time is done, drain sauce from ribs, and pour into a sauce pan. Combine 1 teaspoon cornstarch with a small amount of cold water, stir into sauce, and bring sauce to boil. Cook until sauce has reached desired thickness.