# ============================================================================
#
# XML Topic Maps 2.1
#
# Proposal for a XML Topic Maps syntax that is backwards compatible to XTM 2.0
#
# Issues:
# * Two reification mechanisms, either as attribute 'reifier' which points 
#   to a topic by an item identifier or as element 'reifier' which can point
#   to a topic by an item identifier, a subject identifier or a subject 
#   locator (the correct, TMDM-compatible way).
#
#   Possible solutions: 
#   * Remove the 'reifier' element and accept that the reifying topic is 
#     only referencable by an item identifier
#   * Remove the reifier attribute -> break compatibility to XTM 2.0 (bad)
#   * Accept both reification mechanisms (preferable)
#
# ============================================================================

# --- Common declarations

default namespace = "http://www.topicmaps.org/xtm/"
namespace xtm = "http://www.topicmaps.org/xtm/"

datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"

start = topicMap

reifiable = (attribute reifier { xsd:anyURI } | reifier)?, itemIdentity*

reifier = element reifier { topic-reference }

href = attribute href { xsd:anyURI }

any-markup = (text | element * - xtm:* { attribute * { text }*, any-markup* })*


# --- The schema

topicMap = element topicMap { reifiable, version, mergeMap*,
                              (topic | association)* }

version = attribute version { ("2.0" | "2.1") }

topic = element topic { ((id, (itemIdentity | subjectIdentifier | subjectLocator)*)
                         |(id?, (itemIdentity | subjectIdentifier | subjectLocator)+)), 
                        instanceOf?, (name | occurrence)* }
id = attribute id { xsd:ID }

name = element name { reifiable, type?, scope?, value, variant* }

value = element value { text }

variant = element variant { reifiable, scope, (resourceRef | resourceData) }

scope = element scope { topic-reference+ }

instanceOf = element instanceOf { topic-reference+ }

type = element type { topic-reference }

occurrence = element occurrence { reifiable,
  type, scope?, ( resourceRef | resourceData ) }

datatype = attribute datatype { xsd:anyURI }

resourceData = element resourceData { datatype?, any-markup }

association = element association { reifiable, type, scope?, role+ }

role = element role { reifiable, type, topic-reference }

topic-reference = (topicRef | subjectIdentifierRef | subjectLocatorRef)

topicRef = element topicRef { href }
subjectIdentifierRef = element subjectIdentifierRef { href }
subjectLocatorRef = element subjectLocatorRef { href }

resourceRef = element resourceRef { href }
subjectLocator = element subjectLocator { href }
subjectIdentifier = element subjectIdentifier { href }
itemIdentity = element itemIdentity { href }

mergeMap = element mergeMap { href }

# --- End of schema