Hello Ken,
Thanks for the model.
I am afraid I didn't use the correct terminology in my response to Terry. I used the term duration, where I should have used the term period.
Let me give an example of the usage of those two periods.
Suppose we want to record the employment of persons, and we don't want to lose any information we ever entered in the database.
To do so we create a quaternary relation with: person, organization, validity period, transaction period.
Let's say we recorded that person 1, has worked for organization A since 1-1-2004, and we stored this fact on 28-3-2006, when the new application to store this information went into production.
{person: 1, organization: A, validity: [1-1-2004, ...], transaction: [28-3-2006, ...]}
Now on 29-3-2006 we discovered a clerical error. Person 1 started working for organization A on 1-2-2004.
We close the transaction period of the original fact.
{person: 1, organization: A, validity: [1-1-2004, ...], transaction: [28-3-2006, 29-3-2006]}
and we create a new fact reflecting the correct validity
{person: 1, organization: A, validity: [1-2-2004, ...], transaction: [29-3-2006, ...]}
Now on 1-1-2014 Person 1 leave company A to start working for company B, and we register that the following day.
We close the transaction period of the current employment fact.
{person: 1, organization: A, validity: [1-2-2004, ...], transaction: [29-3-2006, 1-2-2014]}
we create a new fact that reflects the ending of the validity period.
{person: 1, organization: A, validity: [1-2-2004, 1-1-2014], transaction: [1-2-2014, ...]}
and add a new fact related to the employment with organization B
{person: 1, organization: B, validity: [1-1-2014, ...], transaction: [1-2-2014, ...]}
In short:
The transaction period tells us during which time frame a fact is stored in the logical database (it remains present in the physical database, we never delete or update facts).
The validity period tells us for which time frame a fact holds to be true.
I hope this better explains what I said in too few words in my response to Terry.
Niels