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TDWI Blog: Data 360

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Big Data Analytics: Preparing Analytic Data Differs from ETL for Data Warehousing

Blog by Philip Russom
Research Director for Data Management, TDWI

While researching a new TDWI report on big data analytics, I’ve run across a few BI professionals who are concerned about the seeming lack of data preparation that’s common with some forms of advanced analytics. Allow me a moment to sort this out.

On the one hand, all of us in BI and data warehousing are indoctrinated to believe that the data of an enterprise data warehouse (EDW) (and hence the data that feeds into reports) must be absolutely pristine, integrated and aggregated properly, well-documented, and modeled for optimization. To achieve these data requirements, BI teams work hard on extract, transform, and load (ETL), data quality (DQ), meta and master data management (MDM), and data modeling. These data preparation best practices make perfect sense for the vast majority of the reports, dashboards, and OLAP-based analyses that are refreshed from data warehouse data. For those products of BI, we want to use only well-understood data that’s brought as close to perfection as possible. And many of these become public documents, where problems with data could be dire for a business.

On the other hand, preparing data for advanced analytics requires very different best practices – especially when big data is involved. The product of advanced analytics is insight, typically an insight about bottom-line costs or customer churn or fraud or risk. These kinds of insights are never made public, and the analytic data they’re typically based on doesn’t have the reuse and publication requirements that data warehouse data has. Therefore, big data for advanced analytics rarely needs the full brace of ETL, data quality, metadata, and modeling we associate with data from an EDW.

In fact, if you bring to bear the full arsenal of data prep practices on analytic datasets, you run the risk of reducing its analytic value. This is ironic, because we usually think of ETL, DQ, and data modeling as adding value to data, not subtracting it. So, how can they harm analytic data?

To answer that question, let’s first take a look at so-called “advanced analytics.” This collection of analytic techniques would be better called “discovery analytics,” because that’s what users do with it. A business analyst or similar user applies techniques like data mining, statistical analysis, complex SQL, MapReduce, and natural language processing to discovery facts about the business that no one knew before. For example, you might discover the root cause of the latest form of customer churn. Or you might find a cluster of transactions that indicate a new kind of fraud. Or you could stumble onto an untapped customer segment.

In general, you can’t discover those entities and facts from the overly studied, calculated, modeled, and aggregated data of an EDW. Instead, you need big data, with lots of granular detail, typically in the schema of the source systems it came from. Some forms of analytics actually thrive on questionable data in poor condition. For example, analytic applications for fraud detection may depend on outliers and non-standard data as indications of fraud. And the insights of discovery analytics often focus in narrow slices of the business, like an obscure customer segment, or time frame or group of shipments or transaction types or risky neighborhood. These thin slices can easily disappear in an aggregation pass. Hence, if you apply ETL and DQ processes to big data, as you do for a data warehouse, you run the risk of stripping out the very nuggets that make big data a treasure trove for discovery oriented advanced analytics. This is why the preparation of data for discovery analytics seems minimal (even slipshod) – often just extracts and table joins – compared to the full range of data prep applied to EDW data.

Does this mean that we can throw out the sacrosanct best practices for ETL, DQ, metadata, MDM, and data modeling? No, of course not. Some organization will simply need to suspend these for discovery analytics with big data—but only temporarily. Here’s a typical scenario.

After business analysts and other users have discovered what they’re looking for in big data, they need to take the discovery to the BI and DW team, so the results can be “institutionalized” in the EDW. For example, when discovery analytics reveals valuable items – like new forms of churn, customer segments, cost centers, etc. – these need to be represented by data structures in the EDW and reports, so that business people can track them regularly. At that point, the best practices of data preparation come back into play.

So, what do you think, folks? Let me know. Thanks!

Posted by Philip Russom, Ph.D. on July 12, 2011


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