How can RDF documents be linked together to allow crawlers and user agents to navigate between them?
Linked Data is typically discoverable by de-referencing URIs. Starting with a single URI a user agent can find more data by discovering other URIs returned by progressively retrieving descriptions of resources referred to in a dataset. However in some cases it is useful to provide additional links to other resources or documents. These links are not semantic relations per se, just hypertext links to other sources of RDF.
The Linked Data published by the BBC Wildlife Finder application includes data about ecozones. The data about an individual ecozone, e.g. the Nearctic Ecozone refers to the habitats it contains and the species that live in that ecozone. A semantic web agent can therefore begin traversing the graph to find more related data. The RDF document returned from that URI also includes a seeAlso relationship to another document that lists all ecozones.
The rdfs:seeAlso relationship is intended to support some hypertext links between RDF documents on the web. There are no explicit semantics for the property other than that a user agent might expect to find additional, relevant RDF data about a resource at the indicated location. Using this relationship allows documents to be linked together without requiring semantic relations to be specified between resources where none exists.
By ensuring that data from a Linked Data site is robustly linked together, it helps semantic web crawlers and user agents to traverse the site to find all relevant material. The rdfs:seeAlso relation is therefore well-suited for publishing simple directories of links for a crawler to follow.
The relation can also be used to refer to other documents on the web, e.g. published by third-parties, that may contain additional useful Annotation data.