Some complex equipment such as circa 1990 office copiers have keys called operator keys kept by certain office personnel who have extra knowledge of the copier. There may also be service keys held be even fewer people for use on even rarer events. The copier, as an object, presents multiple facets, one to the general user and to others via different keys.
The service key to the copier is a nearly perfect analog to the capability style service key. The use of the service key to an object is generally in support of the object's normal use via its main key. The main key and service key are two facets to the object.
Another metaphor for the service key is the difference between the authority to get back-stage in a theater and the authority to attend a performance. The purpose for back-stage access is to improve the illusions for the audience with the authority to attend the performance. Neither of these implies the other but in the capability examples of this pattern that we know of, the service key will generally produce the use key.
In these cases the complexity revealed in the semantics of the service key need be coped with only by specialized programs where the general usage of the object is kept simple and uniform. The object is simple to most but complex to a few. It is generally necessary to limit the distribution of the service key in order insure the proper behavior of the usage key. Users of the usage key rely on the correctness of programs that use the service key.
As with the office copier, different brands of copiers will require different specialized knowledge where the general usage of the copier does not require special knowledge. The same is true of capability service keys.
Again with the office copier different offices may set diffeerent policies on copier use via service keys. The pattern too extends to capability service keys.
The write key to a page might be viewed as a service key to that page where the use key is the read key. We avoid this usage since Keykos segments have deeper sorts of service than writing.