A <schemeref> element references another subject
scheme map. Typically, the referenced subject scheme defines a base set of controlled
the referencing map then extends the base set of controlled values. The values specified
subject scheme maps are merged; the result is equivalent to specifying all of the
values in a
The <hasInstance> element specifies that the contained subjects
have an INSTANCE-OF relationship with the container subject. In an INSTANCE-OF hierarchy,
child subject is a specific entity or object and the parent subject is a type, kind,
or class of
entity or object.
For subjects within the <hasNarrower> element, the container
subject is more general than each of the contained subjects. That is, this element
default hierarchical relationship explicit, although the way in which a relationship
is not specified.
The <elementdef> element identifies an element to
which an attribute is bound. If the <enumerationdef> element does not
contain an <elementdef> element, the enumeration is bound to the
attribute in all elements.
The <attributedef> element specifies the attribute that is bound
to a set of controlled values. This binding restricts the permissible values for the
attribute to those that are contained in the set of controlled
The <defaultSubject> element is used within an attribute
enumeration to set the default value for the attribute in cases where no value is
the attribute. The default subject must be one of the controlled values that are bound
The <subjectHead> element provides a heading for a group of
subjects, for use if the scheme is displayed. For instance, a schememight be displayed to let a user select subjects as part of faceted browsing. The
<subjectHead> element itself does not reference a file and cannot be
referenced as a key, so it does not define any controlled values.
The <subjectdef> element defines a subject (also known as a
controlled value) within a subject scheme. The @keys attribute specified on
the <subjectdef> element assigns a key to the subject. A subject with
a key can be addressed using a @keyref attribute.
The <relatedSubjects> element establishes associative
relationships between each child subject and every other child subject (unless the
restricted by the @linking attribute of the subjects).
The <subjectRelTable> element is a specialized relationship table
which establishes relationships between the subjects in different columns of the same
element provides an efficient way to author non-hierarchical relationships between
Tools (such as search tools) that use subject relationships to find related content
might use these associative relationships in a similar way to the
The <subjectRel> element contains a set of subjects that are
related in some manner. Each group of subjects is contained in a
<subjectRole> element; the associations between different columns in the same
row are evaluated in the same way as those in a <relrow> (from which
<subjectRel> is specialized) but define relationships between
the subjects instead of links between topic documents.
The <subjectRole> element, when used within a
<subjectRel> element, contains a set of subjects that are related to other
subjects in the same row of the current <subjectRelTable>. By default, no
relationship is defined between multiple subjects in the same <subjectRole>
element. When used within the <subjectRelHeader>, the
<subjectRole> element defines the category of subject or relationship
provided by that column.