A non-delta member can be read simultaneously by several users; it can, however, be written to by one user only. When a non-delta member has been opened for writing, no other access - including read access - to this member can be performed, but access to other non-delta members of the library is possible.
A delta member can be read simultaneously by more than one user.
If a delta member is open for writing, then no members in the data tree concerned which are of the same type and have the same name can be read or written to by other users.
As a result of the multiple access options to a library a member may still exist while the directory is being listed, but be no longer in existence when it is subsequently accessed: another user has deleted it in the meantime.
A listing of the library’s directory (see the LMS statement SHOW-ELEMENT-ATTRIBUTES) will therefore only show the current state of the input library.
The user is responsible for the logical coordination of accesses to the library members.