DITA provides a number of facilities for establishing relationships among DITA elements and between DITA elements and non-DITA resources. All DITA relationships use the same addressing facilities irrespective of the semantics of the relationship established. DITA addresses are either direct, URI-based addresses, or indirect key-based addresses. Within DITA documents, individual elements are addressed by unique IDs specified on the common @id attribute. DITA defines two fragment identifier syntaxes for addressing DITA elements, one for topics and elements within maps and one for non-topic elements within topics.