A needle is either "a slender, solid, usually sharp-pointed instrument used for puncturing tissues, suturing, or passing a ligature around or through a vessel" - Farlex Partner Medical Dictionary, or "a fine hollow tube, with a cutting tip, used to access subdermal tissues; used in conjunction with a syringe to administer fluid agents (e.g. local anesthetic), collect blood or aspirate fluids." - Illustrated Dictionary of Podiatry and Foot Science. This class represents a needle which may be specified in a protocol, a procedure order, or in the documentation of a procedure performed. While we are primarily thinking of hollow needles, this class can be used for both solid and hollow needles as the properties of gauge and length apply to both. It is noted that needles are technically a kind (i.e., a subtype) of Device, but we have modeled Needle as a type of Product, since needles are fungible commodities and because there is no need to assign or track serial numbers to individual needles.