A nature is a thing, which is connected to its resource with the property
http://www.w3.org/2005/12/assoc#nature:

(a resource) -> (the nature property) -> (a specific nature)

Natures include the following:

  http://niem.gov/niem/resources/natures#zargo
    The nature of a Zargo (ArgoUML) binary file.
    There is no official MIME type available for this.  Another option
    may be http://www.iana.org/assignments/media-types/application/x-zargo.

  http://niem.gov/niem/wantlist/1
    The nature of a NIEM Wantlist, version 1.

  http://schema.omg.org/spec/XMI/2.1
    An XMI file, version 2.1
    Make the obvious substitution if you are using a different version
    of XMI

  http://www.ascc.net/xml/schematron
    Schematron schema

  http://www.iana.org/assignments/media-types/application/msword
    Microsoft  Word document

  http://www.iana.org/assignments/media-types/application/octet-stream
    Other  binary file

  http://www.iana.org/assignments/media-types/application/pdf
    PDF file

  http://www.iana.org/assignments/media-types/application/vnd.visio
    Visio  drawing (VSD)

  http://www.iana.org/assignments/media-types/image/jpeg
    JPEG image

  http://www.iana.org/assignments/media-types/text/plain
    Text file

  http://www.iana.org/assignments/media-types/text/xml
    An XML file

  http://www.w3.org/2000/10/XMLSchema
    The nature of a W3C XML Schema.

  http://www.w3.org/1999/XSL/Transform
    The nature of an XSLT file.
      + Found at http://www.rddl.org/purposes/software[2]

  http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict
     The nature of XHTML 1.0 Strict

  http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional
    The nature of XHTML 1.0 Transitional.

  http://schemas.xmlsoap.org/wsdl/
    A WSDL file, in XML.

  http://www.iana.org/assignments/media-types/application/zip
    Zip file