Generating a Table of Contents in DITA
In DITA, the order and hierarchy of the table of contents of a document is based directly on
        the DITA map that defines the
        document. In most cases, the processor generates a table of contents (TOC) based on
      the hierarchy of the topics in a DITA map. By default, each <topicref> element
      in a map represents a node in the TOC.
It is also possible to instruct DITA where the table of contents should occur (or other
      content lists, such as a list of figures or tables). If you want to instruct the processor to
      generate a table of contents at a particular location within your DITA map structure, you can
      use the <toc> element in a bookmap (as in the
      example below). For more information about the <toc> element, see https://docs.oasis-open.org/dita/v1.2/os/spec/langref/toc.html.
<bookmap>
.....
  <frontmatter>
    <booklists>
      <toc href="chapter1.dita"/>
    </booklists>
  </frontmatter>
.....