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These routines use the terminology ``item'' to
refer to either a structured noticeboard object (ie, one with no values
but possibly having lower-level objects) or to a primitive noticeboard
object (ie, one with a shape and with values). The terms
``item identifier'', ``identifier'' or ``ID'' refer to ``handles'' (cf HDS
locators) which allow access to all information pertaining to an item. As
far as callers are concerned these are just integers. As far as the
noticeboard system is concerned they are pointers to data structures
called ``item_descriptor''s. In the routine specifications they are
regarded as integers. A zero ID is always an invalid ID and all routines
will detect an attempt to use a zero ID. Similarly all routines that
return ID's will return zero ID's on failure. Note that there is a danger
of an access violation if true garbage ID's are passed. This is unlikely
to happen, because of the use of the modified status convention.
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NBS The Noticeboard System
Starlink User Note 77
D.J. Allan
11 September 1995
E-mail:ussc@star.rl.ac.uk