Slides of talk given on 10.09.2014 introducing temporal databases.

1. Text
Tracking your Data Across the Fourth Dimension
Wellington Waterloo Web Makers Meetup

2. “In physics, spacetime is any mathematical model
that combines space and time into a single
interwoven continuum.”
–Wikipedia

3. Databases are Good at
‘Now’
CRUD
Create data
Read data
Update data
Delete data

4. Bread and Butter Queries
How many people work
in department X?
What’s the total amount
paid in commissions by
department?
What was the top selling
product in the last year?

5. The Fourth Dimension…
Compare reporting
relationships one month ago,
today and in one months time
Show me all changes made
to this data over time
As of one month ago, what
did I believe to be the truth
about this data yesterday and
what did I actually believe
was the truth yesterday?

6. “A temporal database is a database with built-in
support for handling data involving time…”
–Wikipedia
”

7. A Little History…
Need for temporal support identified as early as 1992
Initial attempts to get support for this into the SQL
standard were rejected
Finally made it into the SQL:2011 standard

8. Some Sample Data
Owner Property
Jeremy ‘Some place’

9. What forms of temporal data
are usually stored?

10. Temporal Aspects
Decision Time
Valid Time
Transaction Time
A table that implements one of these is temporal, two
is bi-temporal, more is multi-temporal

11. Decision Time
Records when a decision was taken
Stored as a timestamp
You may be doing this already…

12. Decision Time Example
Owner Property Decision Time
Jeremy ‘Some place’ 2012-09-28
Adam ‘Some place’ 2014-02-21

13. Valid Time
The time during which a fact is true with respect to the
real world
Modelled as a range between two timestamps
Closed at lower bound, can be open at upper bound

14. Valid Time Example
Owner Property StartVT EndVT
Jeremy ‘Some place’ 2012-09-28 2014-02-20
Adam ‘Some place’ 2014-02-21 ∞

15. Valid Time Example
Owner Property StartVT EndVT
Jeremy ‘Some place’ 2012-09-28 2014-03-20
Adam ‘Some place’ 2014-03-21 ∞

16. Transaction Time
The time period during which a fact stored in the
database is considered to be true
Modelled as a range between two timestamps
Closed at lower bound, can be open at upper bound

17. Transaction Time Example
Owner Property StartVT EndVT StartTT EndTT
Jeremy ‘Some
place’
2012-09-2
8
2014-02-2
0
2012-09-2
8
2014-09-0
9
Adam ‘Some
place’
2014-02-2
1 ∞ 2014-02-2
1
2014-09-0
9
Jeremy ‘Some
place’
2012-09-2
8
2014-03-2
0
2014-09-0
9 ∞
Adam ‘Some
place’
2014-03-2
1 ∞ 2014-09-0
9 ∞

18. Valid Time and Transaction
Time are Orthogonal
Valid Time
Transaction Time

19. Enough theory! How do I add
this stuff to my db schema?

20. SQL:2011 Temporal
Additions
!
PERIOD type for date ranges in table definitions
Can query for data in a period using new predicates
CONTAINS, OVERLAPS, EQUALS, PRECEDES and
IMMEDIATELY SUCCEEDS
Can also update or delete data matching a portion of a
period using FOR PORTION OF {period_name} FROM
{date} TO {date}

21. Implementing Valid Time
Done by adding columns for start and end with a
period constraint on the columns
Period must also be included as part of the primary key

22. Table Definition using Valid
Time
CREATE TABLE Emp(
ENo INTEGER,
StartVT DATE,
EndVT DATE,
EDept INTEGER,
PERIOD FOR EValidTime (StartVT, EndVT),
PRIMARY KEY (ENo, EValidTime WITHOUT OVERLAPS),
)

23. Foreign Key Problems…
It’s possible that rows in child tables may reference
rows in parent tables that are not currently valid and
vice versa
Therefore foreign key constraints have to be updated
where needed to include period data

24. Valid time foreign key
definition
ALTER TABLE Emp
ADD FOREIGN KEY (Edept, PERIOD EValidTime)
REFERENCES Dept (DNo, PERIOD DValidTime)

25. Querying a Table using Valid
Time
SELECT Ename, Edept
FROM Emp
WHERE ENo = 22217 AND
EValidTime CONTAINS DATE ‘2011-01-02’;
!
SELECT Ename, Edept
FROM Emp
WHERE ENo = 22217 AND
EValidTime OVERLAPS
PERIOD (DATE ‘2010-01-01', DATE ‘2011-01-01');

26. Implementing Transaction
Time
RDBMS automatically creates a snapshot when data is
updated or deleted
Done by adding columns for start, end and a period for
them
Must also add WITH SYSTEM VERSIONING to create
table statement

27. Table Definition using
Transaction Time
CREATE TABLE Emp
ENo INTEGER,
Sys_start TIMESTAMP(12) GENERATED
ALWAYS AS ROW START,
Sys_end TIMESTAMP(12) GENERATED
ALWAYS AS ROW END,
EName VARCHAR(30),
PERIOD FOR SYSTEM_TIME (Sys_start, Sys_end)
) WITH SYSTEM VERSIONING

28. Querying a Table using
Transaction Time
SELECT ENo,EName,Sys_Start,Sys_End
FROM Emp FOR SYSTEM_TIME AS OF
TIMESTAMP '2011-01-02 00:00:00’;
!
SELECT ENo,EName,Sys_Start,Sys_End
FROM Emp FOR SYSTEM_TIME FROM
TIMESTAMP '2011-01-02 00:00:00’TO
TIMESTAMP '2011-12-31 00:00:00’;

29. Bi-Temporal table definition
CREATE TABLE Emp(
ENo INTEGER,
StartVT DATE,
EndVT DATE,
EDept INTEGER,
PERIOD FOR EValidTime (StartVT, EndVT),
Sys_start TIMESTAMP(12) GENERATED ALWAYS AS ROW START,
Sys_end TIMESTAMP(12) GENERATED ALWAYS AS ROW END,
EName VARCHAR(30),
PERIOD FOR SYSTEM_TIME (Sys_start, Sys_end),
PRIMARY KEY (ENo, EValidTime WITHOUT OVERLAPS),
FOREIGN KEY (Edept, PERIOD EValidTime)
REFERENCES Dept (DNo, PERIOD DValidTime)
) WITH SYSTEM VERSIONING

30. Who supports SQL:2011
Temporal?
IBM DB2. Called “Time Travel Queries”, although
different syntax for FOR SYSTEM_TIME AS OF
Oracle 12c, in compliance with SQL:2011
Others?

31. Further Reading
‘Developing Time Oriented Applications in SQL’ by
Richard Snodgrass
‘Temporal Features in SQL:2011’
‘Time and Relational Theory: Temporal Databases in
the Relational Model and SQL'

32. Thanks for listening
Any questions?
Contact me:
@JCook21
jeremycook0@gmail.com
I’d love some feedback!