Table of contents

Appendices

2.3 Resources in Relation to the Physical Location of a Linking Element

A local resource is an XML element that participates in a link by virtue of having as its parent, or being itself, a linking element. Any resource or resource portion that participates in a link by virtue of being addressed with a URI reference is considered a remote resource, even if it is in the same XML document as the link, or even inside the same linking element. Put another way, a local resource is specified "by value," and a remote resource is specified "by reference."

An arc that has a local starting resource and a remote ending resource goes outbound, that is, away from the linking element. (Examples of links with such an arc are the HTML A element, HyTime "clinks," and Text Encoding Initiative XREF elements.) If an arc's ending resource is local but its starting resource is remote, then the arc goes inbound. If neither the starting resource nor the ending resource is local, then the arc is a third-party arc. Though it is not required, any one link typically specifies only one kind of arc throughout, and thus might be referred to as an inbound, outbound, or third-party link.

To create a link that emanates from a resource to which you do not have (or choose not to exercise) write access, or from a resource that offers no way to embed linking constructs, it is necessary to use an inbound or third-party arc. When such arcs are used, the requirements for discovery of the link are greater than for outbound arcs. Documents containing collections of inbound and third-party links are called link databases, or linkbases.