Artificial example:

Label: Fish in Green Lake
Index terms: fish, lakes, lake fish, Green Lake

Example from USGS web:

http://toxics.usgs.gov/topics/attenuation.html
Labels:
  Toxics Program Projects on Natural Attenuation
    USGS science programs
      and
    Anthropogenic contamination
      and
    Biodegradation
      and
    Contaminant transport
      and
    Geochemical processes
  Headlines
    USGS news
  Natural Attenuation Remediation Related Activities
    Anthropogenic contamination
      and
    Remediation
  Fact Sheets
    Documents
  Bibliographies
    Bibliographies