1. Author: Miran Miklič miran.miklic@gov.si
Comparison and advantages of the Bitemporal and Temporal databases over Tuple-versioning (point-in-time) database systems like SDMX Registry
Author: Miran Miklič

2. Versioning/Temporal/Bitemporal model
Current SDMX Registry
Versioning/Temporal/Bitemporal model
May 2011

3. Current SDMX Code Lists
Versioning/Temporal/Bitemporal model
May 2011

4. Current SDMX – Valid From/To is usually empty
Versioning/Temporal/Bitemporal model
May 2011

5. Versioning/Temporal/Bitemporal model
Versioning problem
Versions enables the people to distinguish the data in time, but there is no metadata needed about time
With different version we can only specify, that the data has been changed, but not when exactly and why
It is very hard to maintain such a system with hundreds or thousands of elements, each with many versions
Versioning/Temporal/Bitemporal model
May 2011

6. Versioning/Temporal/Bitemporal model
Temporal model is the model where Valid time start and end is added
Valid time start should be known, while it is possible not to limit the validity end, can be valid forever or more probable until first change of the data
By changing the data we have to use versioning again to enable tracing, however we have to have the versioning of the whole database and not only the single database table
Versioning/Temporal/Bitemporal model
May 2011

7. Versioning/Temporal/Bitemporal model
Events in time can be used as a basis of changing the data
Bitemporal is the model with Valid time and Transaction time
Transaction time is part of the Timeline
Individual data can be changed each with different timeline
Model enable greatest flexibility which is common in daily life
Bitemporal model can be user also for the life of data columns but slightly different than usual, instead of deleting the column we can simply stop changing the column and we can create new one
Versioning/Temporal/Bitemporal model
May 2011

8. Versioning/Temporal/Bitemporal model
Valid Time
Valid time is the time when the data has specified value
Because of that Valid Time has to have start and end
If the end is not specified it is considered to be valid from start, is valid Now and until first change of the data
Versioning/Temporal/Bitemporal model
May 2011

9. Versioning/Temporal/Bitemporal model
Transaction Time
Transaction time start is the time of entering the new data
Transaction time end is until first change of the data value, for new data is not specified because it is not known yet
Transaction time is a unique part of the timeline, however timeline can be partitioned as to the desired time slice as necessary (daily, monthly etc.)
During queries we can limit the Transaction time start to the desired value and effectively limit the time period for the included changes of the data
Versioning/Temporal/Bitemporal model
May 2011

10. Versioning/Temporal/Bitemporal model
About Codebooks
Instead of text we use some key code which is shorter than the text and we store the key code and key text combinations in the separate file
Codebooks are usually treated just as simple table
By creating Codebooks we have separated the coded data from the key text
Codebooks tend to have the independent life of its own
It is not common to have central managing of the codebooks, tracking of the changes and have always somebody responsible for the individual codebook
Versioning/Temporal/Bitemporal model
May 2011

11. Versioning/Temporal/Bitemporal model
Bitemporal Codebook
SORS have very positive experience with the codebook organized according to the Temporal model
Bitemporal model offers also additional tracking of the data changes
We can have one or more codebooks organized according to Bitemporal model and we eliminate the problem of the separation the coded data from the coded test with using the time to join the code and text
Versioning/Temporal/Bitemporal model
May 2011

12. Some rules: errors and changes
Always mark the nature of the data changes in the database, whether is the change of the data based on the facts or it is just the correction of the errors. It can be essential for some researches like migrations
Database should have the ability to eliminate errors during queries
Versioning/Temporal/Bitemporal model
May 2011

13. Some rules: golden rules for tables
Primary key is unique and is never changed; sequence number is the best candidate
Primary key should have no relation with the data, do not use Social security number, Tax number, centroid etc. as primary key, such data are data which can be changed!
No data record is ever deleted, they are only mark as deleted or in case of the Bitemporal model Transaction-time End is set.
Do not assign the primary key of the deleted data to different piece of the data, not applicable to Bitemporal model (hopefully)
Versioning/Temporal/Bitemporal model
May 2011

14. Bitemporal model – Time split and Time join
New functionality specific to the Bitemporal model is Time split and Time join
Time split on the given date to produce two databases which consist only of the data up to the given date and from the given date. Appropriate end and start data values should be interpolated.
Time join of the two databases; end and start data values should be eliminated.
Versioning/Temporal/Bitemporal model
May 2011

15. Bitemporal Database with Timeline
Simplified model of the new SDMX Registry is shown as an example of the Bitemporal Database with the Single Timeline
Primary Key is the join element and is basically the Event sequence number
Validation and Transaction dates are only in the single Timeline table
Codebooks are also in the single table with the common Primary Key column
All other tables can be created as usually with adding only common Primary Key column
Versioning/Temporal/Bitemporal model
May 2011

16. Bitemporal Database with Timeline - shematics
Versioning/Temporal/Bitemporal model
May 2011

17. Proposed Login to SDMX Registry
Versioning/Temporal/Bitemporal model
May 2011

18. Versioning/Temporal/Bitemporal model
SQL/Temporal
SQL/Temporal has been proposed to be ISO SQL 2003 standard
Project has been canceled due to the lack of progress
In late 2010 commercial firms started to support the Bitemporal model building on the guidance from SQL/Temporal initiative
It is expected that during this year some kind of SQL/Temporal will be standardized as ISO standard
Versioning/Temporal/Bitemporal model
May 2011

19. Versioning/Temporal/Bitemporal model
Thank you Questions?
Versioning/Temporal/Bitemporal model
May 2011