A purpose is a property of a resource.  For example, a resouce that
has a change long has the RDF model

(a resource) -> (the change log purpose proprty) -> (a specific change
log file)

  http://niem.gov/niem/resources/purposes#business-requirements
    itemized  descriptions; may also contain business rules
  
  http://niem.gov/niem/resources/purposes#business-rules
    May be: (1) plain or structured English, (2) written into master
    documentation, (3) Schematron or other formal business rule language,
    (4) generated by a development tool

  http://niem.gov/niem/resources/purposes#catalog
    List of artifacts in the IEPD; machine readable; open, portable
    format; browser displayable

  http://niem.gov/niem/resources/purposes#change-log
    A change log.

  http://niem.gov/niem/resources/purposes#constraint-schema
    Constraints  for separate constraint validation path; a compressed
    directory of schemas (to distinguish from other schema sets)

  http://niem.gov/niem/resources/purposes#domain-model
    Domain model in standard open format (xmi, vsd, zargo) and standard
    open graphic (jpg, pdf, etc.); likely a Unified Modeling Language
    (UML) model

  http://niem.gov/niem/resources/purposes#endorsement-letters
    documentation from professional or governmental organizations that
    confirm support; refer to Endorsement in metadata

  http://niem.gov/niem/resources/purposes#exchange-schema
    Base document schema that defines the xml root element, generally
    named after the IEPD itself; AKA document schema, reference schema,
    root schema

  http://niem.gov/niem/resources/purposes#extended-components
    Components created because they were not in NIEM; may be part of
    mapping spreadsheet; include structure and definitions of new components;
    prefer Component Mapping Tool (CMT)

  http://niem.gov/niem/resources/purposes#extension-schema
    Specification for extended components; separate local namespace;
    components not contained in NIEM

  http://niem.gov/niem/resources/purposes#mapping
    Mapping of domain components to NIEM components; tagged with constraints
    (i.e. cardinality, etc.); prefer Component Mapping Tool

  http://niem.gov/niem/resources/purposes#master-documentation
    May  include purpose, business requirements, what, when, why, how
    to, etc.; need guidelines for Master Documentation content; the
    following indented items are possible documents that can be contained
    with the Master Documentation or broken out as individual files.

  http://niem.gov/niem/resources/purposes#metadata
    All metadata registered with the IEPD

  http://niem.gov/niem/resources/purposes#methodology-and-tools
    Used  to build IEPD; may contain URLs or references to tools, methodology,
    documentation

  http://niem.gov/niem/resources/purposes#memorandum-of-understanding
    Memorandums  of Understanding among participating agencies

  http://niem.gov/niem/resources/purposes#reference-schema
    A reference schema, as opposed to some other type of schema used
    for validation.
      + A specialization of http://www.rddl.org/purposes#schema-validation

  http://niem.gov/niem/resources/purposes#sample-instance
    Example  instance; may be multiple; may reference optional style
    sheet

  http://niem.gov/niem/resources/purposes#sample-xslt
    Example style sheet for display of instances; may be multiple

  http://niem.gov/niem/resources/purposes#subset-schema
    A reference schema, as opposed to some other type of schema used
    for validation.

  http://niem.gov/niem/resources/purposes#testing-and-conformance
    Description  and results of validation and conformance testing
    performed; may include testing output or products

  http://niem.gov/niem/resources/purposes#want-list
    A NIEM SSGT want list.
      + A specialization of http://www.rddl.org/purposes#schema-validation

  http://www.rddl.org/purposes#non-normative-reference
    A non normative reference is a document whose definitions are not
    normative to the referencing document.

  http://www.rddl.org/purposes#schema-validation
    A schema to be used for validation

  http://niem.gov/niem/resources/purposes#use-case-model
    Use case diagram in standard open format and standard graphic; likely UML

  http://niem.gov/niem/resources/purposes#endorsement-letters
    Documentation from professional or governmental organizations that confirm support;
    refer to Endorsement in metadata

  http://niem.gov/niem/resources/purposes#constraint-schema
    Constraints for separate constraint validation path; a compressed directory of schemas
    (to distinguish from other schema sets)

  http://niem.gov/niem/resources/purposes#extended-components
    Components created because they were not in NIEM; may be part of mapping spreadsheet; 
    includes structure and definitions of new components; prefer Component Mapping Tool (CMT)

  http://niem.gov/niem/resources/purposes#wsdl
    WSDL description of a web services interface for the IEPD.