Where to implement SCD type 2 logic?

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Where to implement SCD type 2 logic?

Post  kajaldas007 on Wed Aug 27, 2014 12:01 am

Hello friends,

Recently I joined a program, where the first thing i noticed is that the SCD type 2 logic has been implemented inside the MDM software (in this case, it is Tibco MDM).
Tibco MDM architecture has support for record versioning, among many other features. However, it does not have out-of-the-box support for type 2 logic as such (which is normal and obvious). So, in the past, the previous system integrator did some tweak; they wrote a custom logic for handling type 2 entities in Java and plugged that into the MDM architecture.

Life was smooth for a while until some day when we realized that the custom logic has flaws and has been giving rise to DQ issues.

If you want to know more - like, what exactly the custom logic does, the type of DQ issues, etc, please let me know. I am not mentioning these yet because I am going to ask a fundamental question:

What is the best practice? Should the type 2 logic be implemented in the MDM tool or during dimension load (i.e. in the ETL) in the EDW?

I am not sure if this topic has been already discussed in this forum or any other forum. If it has been, then please provide me the pointer to the same. Thanks in advance.

- Kajal K. Das
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Re: Where to implement SCD type 2 logic?

Post  nick_white on Wed Aug 27, 2014 2:25 am

I don't think there is a correct answer; it depends on your requirements, the capabilities of your toolset, etc.

As you already have an MDM system then my starting point would be to try to implement your SCD logic there - but only if your MDM system supports what you are trying to do. I wouldn't try and force your SCD logic into your MDM system just because you have an MDM system.
If your ETL tool is a better place to implement SCD logic, and the downsides of taking it out of your MDM system are minimal, then do it in your ETL system.
Basically, weigh up the pros and cons of each (any) approach and then pick the best solution for your particular needs

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Re: Where to implement SCD type 2 logic?

Post  kajaldas007 on Wed Aug 27, 2014 2:45 am

Thanks for your reply.
I agree with you.
As I already said, Tibco MDM does not have inbuilt support for type 2 handling. Significant custom coding had to be done to address the problem. even after that all scenarios were not properly covered, e.g. late arriving records, correction records, inferred rows, etc. And these give rise to various DQ issues.
In ETL, definitely, we would have more flexibility.

BTW, is there any MDM tool that can handle type 2 entities?
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Re: Where to implement SCD type 2 logic?

Post  ngalemmo on Wed Aug 27, 2014 5:16 pm

A MDM system is not a suitable mechanism to maintain type 2 dimensions in a data warehouse.

1. A MDM system is not a data warehousing system
2. A MDM system does a lot of stuff that data warehouses do not do and are complex enough as it is.
3. A MDM system has no reason to know what a type 2 dimension is, let alone be able to maintain one.

There are very simple and basic code patterns to read a source and maintain a type 2 dimension. Why complicate things? It's like asking an auto mechanic to do a heart transplant. He could probably do it eventually, but why not save a lot of time and use a heart surgeon?
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Re: Where to implement SCD type 2 logic?

Post  nick_white on Thu Aug 28, 2014 2:09 am

I agree. Having read through these post again I would like to backtrack on my earlier response. The MDM system should provide all the information you require for the source of your SCD dataload (what changed and when) but all SCD logic for loading data should reside in your ETL system

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Re: Where to implement SCD type 2 logic?

Post  kajaldas007 on Thu Aug 28, 2014 11:06 am

Thanks ngalemmo.
I couldn't agree more with you. This is the kind of perspective I was looking for.
Thanks once again.

Thanks nick_white for your concurrence.
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