The "event" entities are the ordered pair in "time sequence" (in historical order) with the time-stamp of "DATE".

　So, the identifier is, as a rule, replicated from the preceding event into the event in back bench--according to the sequence in which the events occurred, as in;
　　order: (order-NO, order-date,...)
　　　　　　　｜
　　　　　　　｜１：Ｎ
　　　　　　　｜
　　bill: (bill-NO, order-NO(R), bill-date, bill-amount,...)

　RULE:
　The identifier (of the preceding event) shall be replicated into the event occurring later in time-sequence.

　There is an exception to the rule.
　The example showed above has the relationship of "one-to-many" between "order" and "bill."
　Take another relationship with the same entities:
　　order: (order-NO, order-date,...)
　　　　　　　｜
　　　　　　　｜Ｎ：１
　　　　　　　｜
　　bill: (bill-NO, order-NO(R), bill-date, bill-amount,...)

　The example shows that a "bill" has a relationship to many "orders" as in a payment in a lump sum.　If the identifier of "order" is replicated into the "bill", the "bill" consists of many records, of the same numbers of "order" records--but a bill is one transaction, not a "header" data for many "detail" transactions, a bill requires no itemization of amounts, it has one and only one amount.
　It's called, mathematic-swise, "many-valued" function.

　In response to "many-valued" function, the rule mentioned above shall be subdivided into two headings:

　(1) in the relationship of "one-to-one" and "one-to-many",
　　The identifier (of the preceding event) shall be replicated into the event occurring later in time-sequence.

　(2) In the relationship of "many-to-one" and "many-to-many",
　　a "mapping-list" shall be prepared as in,

　　order: (order-NO, order-date,...)
　　　　　　　｜
　　　　　　　｜Ｎ：１------- the mapping-list｛order-NO(R), bill-NO(R)｝
　　　　　　　｜
　　bill: (bill-NO, bill-date, bill-amount,...)

　A "mapping-list" is called "taiou-hyo", that sounds like "tie-oh-he-yo".

　Take an example:
　　The order-NO has many values as like 0001, 0002, 0003, 0004, 0005,...and so on.
　　If a bill (with the bill-NO, 001) is for the order-NO, 001, 002 and 004,
　　then the correspondence between the two is posted in the mapping-list;
　　 (001, 0001) (002, 0001) (004, 0001)