Temporal Queries

GProM also support snapshot-reducible semantics, a class of temporal queries which interprets a non-temporal query over a temporal database by showing how the result of the query evolves over time. For example, consider a query that counts the number of items in a warehouse:

SELECT count(*) FROM warehouse;

Interpreted under snapshot semantics over a temporal database the records the content of the warehouse at each point, this query returns how many items are in the warehouse at each point in time.

To evaluate a query under snapshot semantics, you have to wrap it in a SEQUENCED TEMPORAL statement like so:

SEQUENCED TEMPORAL (
    SELECT ...
);

GProM expects the input relation of a snapshot semantics query to associate a time interval with each row that is stored as two attributes (the start and end of the interval). You have specify for every table accessed by the snapshot semantics query the names of these two attributes. For example, if you store time for the warehouse table in attributes time_begin and time_end, then our example query from above would be written as:

SEQUENCED TEMPORAL (
    SELECT count(*)
    FROM warehouse WITH TIME (time_begin, time_end)
);

For example, consider the following GProM session. During time interval [1,2) there are 3 items in the warehouse (cake,fruit, and bacon`).

Oracle SQL - Postgres:[email protected]:gpromtest$SELECT * FROM warehouse ORDER BY time_begin, time_end;
 item  | time_begin | time_end |
--------------------------------
 cake  | 1          | 2        |
 fruit | 1          | 3        |
 bacon | 1          | 10       |
 eggs  | 8          | 18       |
 bacon | 15         | 20       |
Oracle SQL - Postgres:[email protected]:gpromtest$SEQUENCED TEMPORAL (SELECT count(*) AS x FROM warehouse WITH TIME (time_begin, time_end));
| x | t_b         | t_e        |
--------------------------------
| 0 | -2000000000 |          1 |
| 3 |           1 |          2 |
| 2 |           2 |          3 |
| 1 |           3 |          8 |
| 2 |           8 |         10 |
| 1 |          10 |         15 |
| 2 |          15 |         18 |
| 1 |          18 |         20 |
| 0 |          20 | 2000000000 |