固有表現タイプ（MUC）
Message Understanding Conference- 6: A Brief History
https://en.wikipedia.org/wiki/Message_Understanding_Conference
At the sixth conference (MUC-6) the task of recognition of named entities and coreference was added.
For named entity all phrases in the text were supposed to be marked as person, location, organization, time or quantity.
https://cs.nyu.edu/~grishman/NEtask20.book_3.html#HEADING4
ref: https://cs.nyu.edu/~grishman/muc6.html （Wikipediaから）
Named Entities （3タイプ）
ORGANIZATION
named corporate, governmental, or other organizational entity
PERSON
LOCATION
Temporal Expressions（2タイプ）
DATE
TIME
Number Expressions（2タイプ）
MONEY
PERCENT