DITA supports many different linking elements, but they all use the same set of attributes to describe relationships between content.
URI-based links are described by the following attributes.
@href
@href
attribute specifies the URI of the resource that is being
addressed.@format
@format
attribute identifies the format of the resource being
addressed. For example, references to DITA topics are identified with
format="dita"
, whereas references to DITA maps use
format="ditamap"
. References to other types of content should use
other values for this attribute. By default, references to non-XML content use the
extension of the URI in the @href
attribute as the effective
format.@scope
@scope
attribute describes the closeness of the relationship
between the current document and the target resource. Resources in the same information
unit are considered "local"
; resources in the same system as the
referencing content but not part of the same information unit are considered
"peer"
; and resources outside the system, such as Web pages, are
considered "external"
.@type
@type
attribute is used on cross-references to describe the target
of the reference. Most commonly, the @type
attribute names the element
type being referenced when format="dita"
.These four attributes act as a unit, describing whatever link is established by the element that carries them.
The @format
and @scope
attributes are assigned default
values based on the URI that is specified in the @href
attribute. Thus they
rarely need to be explicitly specified in most cases. However, they can be useful in many
non-traditional linking scenarios or environments.
DITA also supports indirect links and cross-references in which a DITA map assigns unique
names, or keys, to the resources being referenced by the publication. This is done using
<topicref>
elements that specify the @keys
attribute. Using the @keyref
attribute, individual links, cross-references,
and images then reference resources by their keys instead of their URIs . Links defined
using @keyref
thus allow context-specific linking behavior. That is, the
links in a topic or map might resolve to one set of resources in one context, and a
completely different set of resources in another, without the need for any modifications to
the link markup.
When links are defined using @keyref
, values for the four linking
attributes described above are typically all specified (or given default values) on the key
defining element.