 
Subject                       topic

Topic identity (id)           
  Referenced by
    Subject locator           URI to network or local resource
    Subject identifier        URI addresses indirectly via subject descriptor
                              to a location to network or local resource
Assertions
  characteristics
    names                     Labels
    occurrences               Particular form of what's it about
    associations              General relationships between subjects

Associations
  Also a topic. Permit nature of each relationship explicit using association
  types. E.g. 'composed by', 'born in'.

  1,2,...Inf                  Any number of subjects
  no direction                created by === has created
  association role type       Also a topic. E.g. 'creator', 'work'
  type-instance
  supertype-subtype

Occurrences 
  Also a topic. E.g. small like date and included in the topic map and is
  called 'internal occurrence'. When larger or for other reason, it can be
  stored externally and referenced via a locator, a URL.

  occurrence type
    E.g. In domain of opera with topics of type composer. 'biography' or 'date
    of birth'. For a topics of type like opera 'synopsis' and 'premier date'
    and for a topics of type city, 'map' would be a choice.

Name
  Also a topic. Can also be typed. Restricted to string.

  variant                     Sort keys, alternative orthographies, misspellings

Scope
Reification
  Reification (literally “thingification”) in the Topic Maps sense of the
  term is defined as 'making a topic represent the subject of another topic
  map construct' in other words, turning a name, occurrence, association role
  (or even the topic map itself) into a topic in order to make assertions
  about the thing it represents.
