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Category: Data Modeling

Power Pivot And Power BI Data Modeling

Avi Singh has a post on data modeling in Power Pivot and Power BI:

It was Greg, who suggested that we form a book reading club. Our first book was one I had heard about, but never read – The Data Warehouse Toolkit: The Definitive Guide to Dimensional Modeling By Ralph Kimball. As a business analyst, I had leaned heavily on Excel, along with a mishmash of other technologies. Data warehouse and data modeling didn’t seem like topics that would be relevant to me; more for an IT/BI team perhaps. But I figured, it couldn’t hurt to learn something new.

Our book club meetings looked more as if, class was in session. We brought in our questions, and Greg patiently answered them, helping us realize the importance of the topics, and trade-offs involved in various choices. As things go, our reading club was disbanded before we were even halfway through the book. But the knowledge that I had gained, helped me grow by leaps and bounds in my Power Pivot and Power BI journey.

Kimball-style fact-dimensional modeling remains a brilliant solution.

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Logical Data Models

Kevin Kline discusses logical data modeling:

In a recent blog post entitled Is Logical Data Modeling Dead?, Karen Lopez (b | t) comments on the trends in the data modeling discipline and shares her own processes and preferences for logical data modeling (LDM). Her key point is that LDMs are on the decline primarily because they (and their creators) have failed to adapt to changing development processes and trends.

I love all things data modeling. I found data models to be a soothing and reassuring roadmap that underpinned the requirements analysis and spec writing of the Dev team, as well as a supremely informative artifact of the Dev process which I would constantly refer to when writing new T-SQL code and performing maintenance. However, as time has passed, I have been surprised by how far it has fallen out of favor.

This is an interesting discussion.  I’m not sure I’ve ever created a true logical data model.  I’ve worked with systems which could potentially take advantage of them, but they never hit the top of the priority list.

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Anchor Modeling

Steph Locke has a presentation on Anchor Modeling as 6th Normal Form:

Anchor Modelling moves you beyond third normal form and into sixth normal form. What does this mean? Essentially it means that an attribute is stored independently against the key, not in a big table with other attributes. This means you can easily store metadata about that attribute and do full change tracking with ease. The historical problem with this methodology is that it makes writing queries a real pain. Anchor Modelling overcomes this by providing views that combine all the attribute data together.

Anchor Modeling is a rather different approach, so if it sounds interesting, check out the tutorial.

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Stop Using Datetime(?)

Kenneth Fisher says to stop using datetime and start using date, time, and datetime2(x):

Why is everyone still using the DateTime datatype exclusively?

Back in SQL 2008 we gained a whole new range of date/time datatypes. Isn’t it about time we started to use them?

In my experience, most of the issue is supporting legacy app code which chokes on these types.  You’d think people would have updated that .NET 2.0 code, but not always.

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T-SQL Tuesday #72

Mickey Stuewe hosted T-SQL Tuesday this month.  Her topic:  data modeling gone wrong.  A few choice posts on the topic follow.

Mickey herself looks at a case in which surrogate keys didn’t quite do the trick:

One of the problems I’ve seen with careless use of surrogate keys are the duplication of natural keys. Quite often it’s overlooked that the natural key still needs to have a unique constraint. Without it, the reporting team ends up having to use MAX or DISTINCT to get the latest instance of the natural key, or SSIS packages are needed to clean up the duplicates. This can be compounded with many-to-many tables.

Surrogate keys are not replacements for natural keys; they are physical implementation mechanisms to make your life easier.

Rob Farley wants you to think about design and whether your warehouse is built in a way that helps the business:

Many data professionals look at a data warehouse as a platform for reporting, built according to the available data sources. I disagree with this.

The models within a data warehouse should describe the business. If it doesn’t, it’s a data model gone wrong.

What is the central thing that your business does? What is the main interest point? What do you need to look after? For me, this forms the core of the warehouse.

Thomas Rushton says name your stuff right.  Picking the right name can be difficult.  “Field1” probably isn’t the right name, though.

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