 Services may also include other services as sub-functions; the main functions of the device are so-called "primary" services, and the auxiliary functions they refer to are "secondary" services.Services, characteristics, and descriptors are collectively referred to as "attributes", and identified by UUIDs.Any implementer may pick a random or pseudorandom UUID for proprietary uses, but the Bluetooth SIG have reserved a range of UUIDs (of the form "" ) for standard attributes.