Question
What is the difference between periodic harvesting and federated harvesting?
Answer
Megan:
Normally services that harvest metadata do so with a number of assumptions. One is that metadata harvested only once and never refreshed loses its usefulness over time. So, if possible, services will reharvest metadata on a periodic basis (depending on how often the information is added to or maintained in some way). This is done by either harvesting the whole set of records again, or by harvesting only updated records, or a combination. The decisions are normally based on whether the site persists deleted records in their sets or not. If they don't, the service provider will need to reharvest the whole set regularly to eliminate deleted records from their service.
Federated harvesting implies a set of agreements to expose and harvest information within a closed group of repositories and services. Repositories don't always register their servers for use by all and sundry, sometimes they create services for more limited use and prefer not to open their information to users they don't know.
Hope this helps.
Regards,
Diane Hillmann
NSDL
http://vrd.askvrd.org/services/answerschema.xml
