input: Write a python function to get author names from a database based on a list of IDs.
  assert get_author_names([1, 2, 3]) == ['Author1', 'Author2', 'Author3']
  assert get_author_names([4, 5, 6]) == ['Author4', 'Author5', 'Author6']
  assert get_author_names([]) == []
output: def get_author_names(ids):
      # Mock database of author names
      author_db = {
          1: 'Author1',
          2: 'Author2',
          3: 'Author3',
          4: 'Author4',
          5: 'Author5',
          6: 'Author6'
      }
      
      # Retrieve author names based on list of IDs
      return [author_db[id] for id in ids if id in author_db]