Every database covers a particular time period . Most databases are indexes . Some databases provide data or the full text of articles. A database is composed of records . Records are composed of fields .
Every database covers particular topics .
Take the time to find out which topics a particular database covers. Choose a database that is appropriate for the research you are doing. Searching a database which does not cover the topic you are interested in is a waste of your time. Every database covers a particular time period . Each database covers material from a particular period of time.