3.1.5.1 Subject scheme maps

A subject scheme map is used to define sets of controlled values for use in classifying content. Sets of controlled values can be bound to DITA attributes. This allows DITA users to share the controlled values for an information set without having to modify a DTD or XML schema. The list of available values can be modified quickly to adapt to new situations, without the need to manage updates to a document type. In addition, DITA users can define relationships between controlled values and extend a set of controlled values maintained by another team or organization. The list of defined values are not validated by basic XML parsers. Instead, the defined values should be validated by DITA processors.

The same core elements in a subject scheme map may be used both to define controlled values and to define hierarchical taxonomies:

schemeref
subjectdef

The following elements are used to bind taxonomies or controlled values to an attribute:

enumerationdef
elementdef
attributedef
defaultSubject

The remaining elements in the subject scheme map are used to make more precise statements about how values in a taxonomy relate to one another.

3.1.5.1.1 subjectScheme
A subjectScheme is a specialized DITA map that defines a collection of controlled values rather than a collection of topics.
3.1.5.1.2 schemeref
A <schemeref> element provides a reference to another scheme. Typically, the referenced scheme defines a base set of controlled values extended by the current scheme. The values in the referenced scheme are merged with the current scheme; the result is equivalent to specifying all of the values in a single map.
3.1.5.1.3 hasInstance
The <hasInstance> element specifies that the contained subjects have an INSTANCE-OF relationship with the container subject. In an INSTANCE-OF hierarchy, the child subject is a specific entity or object and the parent subject is a type, kind, or class of entity or object.
3.1.5.1.4 hasKind
The <hasKind> element specifies that the contained hierarchy expresses KIND-OF relationships between subjects.
3.1.5.1.5 hasNarrower
For subjects within the <hasNarrower> element, the container subject is more general than each of the contained subjects. That is, this element makes the default hierarchical relationship explicit, although the way in which a relationship is narrower is not specified.
3.1.5.1.6 hasPart
The <hasPart> element specifies that the contained hierarchy expresses PART-OF relationships between subjects.
3.1.5.1.7 hasRelated
The <hasRelated> element identifies an associative relationship between the container subject and each of the contained subjects.
3.1.5.1.8 enumerationdef
The <enumerationdef> element identifies one attribute and one or more categories that contain the controlled values for the enumeration. The type attribute has a default value of keys.
3.1.5.1.9 elementdef
The <elementdef> element identifies an element on which an attribute is enumerated. When the <elementdef> is left out of an <enumerationdef> element, the enumeration is bound to the attribute in all elements.
3.1.5.1.10 attributedef
The <attributedef> element specifies the attribute to which a set of controlled values from a subject scheme map are to be applied.
3.1.5.1.11 defaultSubject
The <defaultSubject> element is used within an attribute enumeration to set the default value for that attribute in cases where no value is specified on the attribute. The default subject must be one of the controlled values within the categories specified for the attribute.
3.1.5.1.12 subjectHead
The <subjectHead> element provides a heading for a group of subjects, for use if the scheme is displayed. For instance, a scheme may 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.
3.1.5.1.13 subjectHeadMeta
The <subjectHeadMeta> element allows a navigation title and short description to be associated with a subject heading.
3.1.5.1.14 subjectdef
The <subjectdef> element defines a subject (also known as a controlled value) within a scheme. To make the subject easy to identify, a <subjectdef> may use a keys attribute to assign a key to the subject. A subject with a key can be identified elsewhere with a keyref. The <subjectdef> may use a navtitle element or attribute to supply a label for the subject. The <subjectdef> may also refer to a topic that captures the consensus definition for the subject.
3.1.5.1.15 relatedSubjects
The <relatedSubjects> element establishes associative relationships between each child subject and every other child subject (unless the association is restricted by the linking attribute of the subjects).
3.1.5.1.16 subjectRelTable
The <subjectRelTable> element is a specialized relationship table which establishes relationships between the subjects in different columns of the same row. This element provides an efficient way to author non-hierarchical relationships between subjects. Tools (such as search tools) that use subject relationships to find related content may use these associative relationships in a similar way to the hierarchical relationships.
3.1.5.1.17 subjectRelHeader
The <subjectRelHeader> element specifies the roles played by subjects in associations.
3.1.5.1.18 subjectRel
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.
3.1.5.1.19 subjectRole
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.

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