 The domain or subject matter of patent law is the invention and discovery of new and useful processes, machines, articles of manufacture, or compositions of matter. There are three types of patents recognized by US patent law: utility patents, design patents, and plant patents. Utility patents protect any new, useful, and nonobvious process, machine, article of manufacture, or composition of matter, as well as any new and useful improvement thereof. Design patents protect any new, original, and ornamental design for an article of manufacture. Finally, the subject matter of a plant patent is any new variety of plant that is asexually propagated (e.g. rose bushes grown by cutting pieces of the stem). Patent protection is the strongest form of intellectual property protection, in that a twenty-year exclusive monopoly is granted to the owner over any expression or implementation of the protected work (35 U.S.C. §101 (1988) and 35 U.S.C. §154(a)(2)).