---+ The package metadata file

The package metadata file is a Turtle file at a fixed location in the
package: =|<pack>/rdf/cpack/<pack>.ttl|=.  A template metadata file
can be created using cpack_create/3. See also [[creating][Creating.txt]]
a CPACK.  This file documents the most important properties.

The schema for CPACKS is described in =|rdf/cpack/cpack.ttl|=

The metadata file provides a single resource denotes as =|<>|= (i.e.,
the file itself).  Here are the most important properties

  $ rdf:type <Class> :
  The class is a subclass of cpack:Package. Currently defined subclasses
  are:

    - a *|cpack:Application|* provides human-readable web-pages
    - a *|cpack:Component|* provides a library for building human-readable web-pages
    - a *|cpack:Skin|* specialises layout and presentatio of resources
    - a *|cpack:API|* provides HTTP services (with JSON/XML output)
    - a *|cpack:Library|* provides general computation libraries
    - a *|cpack:Ontology|* provides RDF/OWL schemas

  Many packages provide a mixture. We propose to use the principal role.
  Notably an _application_ may require all the other categories. If some
  of these facilities are considered a candidate for reuse in other
  packages it is better to put these in their own package.

  $ cpack:packageName :
  A literal that gives the package name.  This must match the base-name
  of the GIT repository (without =|.git|= extension).

  $ dcterms:title :
  Short (20-40 character) description of the package that appears in
  the overview table.  Also used for the =description= file of the
  git mirror.

  $ cpack:description :
  Longer text that appears on the package page.

  $ cpack:author :
  Either a URL of a FOAF profile that may be fetched as linked data
  or a blank-node providing at least the author name and foaf:mbox.
  Note that the ClioPatria package server also provides URLs that
  describe users with an account.  The address thereof is the
  address of the server, followed by =|user/<nick>|=.

  $ cpack:primaryRepository :
  Blank node of type cpack:GitRepository, providing the URL
  of the primary GIT repository as cpack:gitURL.

  $ cpack:requires :
  Explicit requirements.  Currently this is a blank node holding a
  cpack:name with the name of the required _token_.  This must be
  matched by another package that _provides_ this token.  Note that
  requirements that can be deduced because one package loads a file
  provided by another package are computed automatically.  Currently
  this is limited to Prolog source-files.

  $ cpack:provides :
  Sub-property of cpack:packageName that provide the name of a
  required _token_.

Below is an example from the package =foaf_user=, which requires =foaf=.

==
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .
@prefix foaf:    <http://xmlns.com/foaf/0.1/> .
@prefix cpack:   <http://cliopatria.swi-prolog.org/schema/cpack#> .
@prefix dcterms: <http://purl.org/dc/terms/> .

<> a cpack:Application ;
        cpack:packageName "foaf_user" ;
        dcterms:title "FOAF profiles for accounts" ;
        cpack:author [ foaf:name "Jan Wielemaker" ;
                       foaf:mbox <mailto:j.wielemaker@cs.vu.nl> ;
                     ] ;
        cpack:primaryRepository
            [ a cpack:GitRepository ;
              cpack:gitURL <git://eculture.cs.vu.nl/home/janw/git/ClioPatria/foaf_user.git>
            ] ;
        cpack:requires [ cpack:name "foaf" ] ;
        cpack:description

"""Manage and view local accounts as FOAF profiles
""" .
==

@see Creating.txt, Submitting.txt, index.txt