Columbia subject headings:
Bibliographical services--Europe--Directories.
EUSIDIC database guide--Periodicals.
Information services--Europe--Directories.
Information storage and retrieval systems--Directories.
Harvard subject headings:
Princeton subject headings:
Information services--Europe--Directories.
Information storage and retrieval systems--Directories.
Machine-readable bibliographic data--Directories.
Online bibliographic searching--Directories.