This image is of a wet sandy beach where someone has written the following
words in the sand:  "WRITING IN THE SAND".  The reason I am using images 
such as this for a webpage about metadata, is that creating metadata is much
like writing in the sand.  The ocean is constantly sending waves to shift 
the sands, and hence requires you to write again and again,
what you wrote before.  
  The world of metadata is much like that right now, in digital libraries.  
The standards keep changing, upgrading, altering, versioning, and the types 
and versions of metadata supported by software and the current whims of the
pack, keep shifting.  
  Whatever you write into one metadata scheme, you will no doubt have to 
write again and again and again, as the waves of change wash over your efforts.