src/Pure/General/rdf.scala

clarified exception;

/*  Title:      Pure/General/rdf.scala
    Author:     Makarius

Support for RDF/XML representation, see also:
  - https://www.w3.org/RDF
  - https://www.w3.org/TR/rdf-primer
*/

package isabelle


object RDF
{
  /* document */

  val rdf: XML.Namespace = XML.Namespace("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
  val dcterms: XML.Namespace = XML.Namespace("dcterms", "http://purl.org/dc/terms/")

  val default_namespaces: List[XML.Namespace] = List(rdf, dcterms)

  def document(body: XML.Body,
    namespaces: List[XML.Namespace] = default_namespaces,
    attributes: XML.Attributes = Nil): XML.Elem =
  {
    XML.Elem(Markup(rdf("RDF"), namespaces.map(_.attribute) ::: attributes), body)
  }


  /* multiple triples vs. compact description */

  sealed case class Triple(
    subject: String, predicate: String, `object`: XML.Body = Nil, resource: String = "")
  {
    require(`object`.isEmpty || resource.isEmpty)

    def property: XML.Elem =
      if (resource.nonEmpty) XML.elem(Markup(predicate, List("rdf:resource" -> resource)))
      else XML.elem(predicate, `object`)
  }

  def triples(args: List[Triple]): XML.Body =
    XML.newline ::
      args.zipWithIndex.groupBy({ case (t, _) => t.subject }).iterator.map(_._2).
        toList.sortBy(ps => ps.head._2).flatMap(ps =>
          List(
            description(ps.head._1.subject,
              XML.newline :: ps.flatMap({ case (t, _) => List(t.property, XML.newline) })),
            XML.newline))

  def description(subject: String, body: XML.Body, attributes: XML.Attributes = Nil): XML.Elem =
    XML.Elem(Markup(rdf("Description"), (rdf("about"), subject) :: attributes), body)


  /* collections */

  def collection(kind: String, items: List[XML.Body]): XML.Elem =
    XML.elem(kind, items.map(item => XML.elem(rdf("li"), item)))

  def bag(items: List[XML.Body]): XML.Elem = collection(rdf("Bag"), items)
  def seq(items: List[XML.Body]): XML.Elem = collection(rdf("Seq"), items)
  def alt(items: List[XML.Body]): XML.Elem = collection(rdf("Alt"), items)


  /* datatypes */

  // see https://www.w3.org/TR/rdf11-concepts/#section-Datatypes
  // see https://www.w3.org/TR/xmlschema-2/#built-in-datatypes

  def string(x: String): XML.Body = if (x.isEmpty) Nil else List(XML.Text(x))
  def bool(x: Boolean): XML.Body = string(x.toString)
  def int(x: Int): XML.Body = string(Value.Int(x))
  def long(x: Long): XML.Body = string(Value.Long(x))
  def double(x: Double): XML.Body = string(Value.Double(x))
  def seconds(x: Time): XML.Body = double(x.seconds)

  val date_format: Date.Format = Date.Format("uuuu-MM-dd'T'HH:mm:ss.SSSxxx")
  def date_time_stamp(x: Date): XML.Body = string(date_format(x))


  /* predicates */

  object Property  // binary relation with plain value
  {
    def title: String = dcterms("title")
    def creator: String = dcterms("creator")
    def contributor: String = dcterms("contributor")
    def date: String = dcterms("date")
    def license: String = dcterms("license")
    def description: String = dcterms("description")
  }

  private lazy val meta_data_table =
    Map(
      Markup.META_TITLE -> Property.title,
      Markup.META_CREATOR -> Property.creator,
      Markup.META_CONTRIBUTOR -> Property.contributor,
      Markup.META_DATE -> Property.date,
      Markup.META_LICENSE -> Property.license,
      Markup.META_DESCRIPTION -> Property.description)

  def meta_data(props: Properties.T): Properties.T =
    props.flatMap({ case (a, b) => meta_data_table.get(a).map((_, b)) })
}