In order to access an HDS object it is first necessary to "associate" a locator with it (like opening a file). This locator can then be used to address the object. When the program no longer needs to access the object the locator should be "annulled" (like closing the file again). A locator is roughly analogous to a Fortran logical unit number (but is actually a character variable, not an integer). The group attribute is used to form an association between objects so that all their locators can be annulled together. A group is written as a character string whose rules of formation are the same as for name.
HDS Hierarchical Data System