They are more than just keywords, allowing richer labeling. Most of the Dublin Core Meta Data Fields are self-explanatory. For Identifier, use the URL for now.
Relation tells what the file is derived from.
Coverage is spatial or temporal, for example, a geographic area such as Ohio. Some people say there is too much involved with metadata and they don't know what to do. Dublin Core is the most widely used, so we can start with that. The metadata systems map from one to another, so Dublin Core can be mapped to other systems later. Dublin Core was developed about five years ago, in Dublin Ohio.