Let's say I have a database to track my customers.
On any given day, a customer is active or non-active, and I can discover this in real-time by querying the database. So, right now, I can easily find out that I have X active customers.
What I can't do is discover how many customers I had on July 5, 2014, for example. There is no way to reconstruct a particular point in time, to find out this data point for any given moment in the past. (Not uncommon -- it would be fairly rare, actually, for a database package to do this. Databases generally know about their state at the current moment only.)
To solve this, I create a job that queries the database every night at midnight, captures this data point, then writes to a file with a date. So, I end up with a series of timestamped numbers which represent this particular point of data at a regular interval over a period of time:
2014-07-05: 82 2014-07-06: 84 2014-07-07: 81 2014-07-08: 76 [etc.]
These numbers represent this data point, trending over time. This is a historical, indisputable record of a single data point at a single, specified moment in time.
Is there a name for this particular aspect/paradigm on this number? What would I call this data set, collectively?