The Data Warrior

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Drill to Detail Podcast: Data Modeling, Data Vault, and Snowflake!

My good friend Mark Rittman has embarked on a new adventure as an independent analyst and consultant. As part of his new venture Mark started a new podcast series on iTunes that he calls Drill to Detail where he will feature interviews discussing a range of topics related to data warehousing, business intelligence, analytics, and big data.

I was honored to be asked to take part in this new venture and got to spend a hour with Mark a few weeks back recording what is now Episode 5 of the series. In this interview we talk about:

The podcast is about 60 minutes with each topic being about 20 minutes (so feel free to skip ahead if you are short on time). Please have a listen and let us know what you think in the comments below.

Cheers!

Kent

The Data Warrior

P.S. I will be speaking on these and related topics at a bunch of events over the next few weeks. Check out my speaking schedule and join me in person if you can!

Maintaining disabled FK’s, wisdom or farce?

A while back, I wrote a post about having FKs (foreign keys) in your data warehouse.

Well, a similar question came up recently on an Oracle forum with the above title. It is a fair question and it does surface fairly regularly in a variety of contexts (not just data warehousing).

Of course, as The Data Warrior, I felt is was my duty to respond.

The Question

Is there any reason to maintain a permanently disabled FK in the data model?  I’m not envisioning a reason to do it.  If it is not going to be enabled, then from my perspective, it would not make any sense to have it defined.  If anything, provide the definition of the relationship in the comment of the child column.

My Answer

Yes, by all means keep the FK please!

I see three good reasons for doing so:

  1. It is valuable metadata (& documentation). If somebody reverse engineers the database (say with ERWin or Oracle Data Modeler), the FK shows up in the diagram (way better than having to read a column comment to find out)
    Data Vault 2.0 Example

    A picture is worth a thousand words!

    .

  2. BI Metadata – If you want to use any sort of reporting or BI tool against the database, most tools will import the FK definition with the tables and build the proper join conditions. Way better than having someone guess what the join will be and then manually adding it to the metadata layer in the reporting tool. Examples that can read the Oracle data dictionary include OBIEE, Business Objects, COGNOS, Looker, and many others.(Note here that since the FK is not enforced on the remote databases, you might want to make sure these are treated as outer joins, lest you lose some transaction in the reports).
  3. The Oracle optimizer will use disabled constraints to improve query performance of joins. Again, this is metadata in the data dictionary which the optimizer can read. This is documented in the Oracle Data Warehouse guide and I have validated it on multiple occasions with Oracle product management.

While #3 applies specifically to Oracle, for other databases like MS SQL Server and Snowflake, #1 and #2 still apply.

Even if only one of the above is true for a given database, that, in my opinion, still justifies keeping the disabled constraint around.

Final Answer = Wisdom

What do you think? Feel free to comment below.

And please share on your favorite social media platform!

Model on!

Kent

The Data Warrior

 

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