Category Archives: Tableau

Bryan Brandow: Triggering Cubes & Extracts using Tableau or MicroStrategy

trigger-720x340

bryan-headshots-004Bryan Brandow (photo, right), a Data Engineering Manager for a large social media company, is one of my favorite bloggers out their in regards to thought leadership and digging deep into the technical aspects of Tableau and MicroStrategy. Bryan just blogged about triggering cubes and extracts on his blog. Here is a brief synopsis.

One of the functions that never seems to be included in BI tools is an easy way to kick off an application cache job once your ETL is finished.  MicroStrategy’s Cubes and Tableau’s Extracts both rely on manual or time based refresh schedules, but this leaves you in a position where your data will land in the database and you’ll either have a large gap before the dashboard is updated or you’ll be refreshing constantly and wasting lots of system resources.  They both come with command line tools for kicking off a refresh, but then it’s up to you to figure out how to link your ETL jobs to call these commands.  What follows is a solution that works in my environment and will probably work for yours as well.  There are of course a lot of ways for your ETL tool to tell your BI tool that it’s time to refresh a cache, but this is my take on it.  You won’t find a download-and-install software package here since everyone’s environment is different, but you will find ample blueprints and examples for how to build your own for your platform and for whatever BI tool you use (from what I’ve observed, this setup is fairly common).  Trigger was first demoed at the Tableau Conference 2014.  You can jump to the Trigger demo here.

I recommend you click on the link above and give his blog post a full read. It is well worth it.

Best regards,

Michael

Tableau Customer Conference 2014 (TCC14): Keynote with Christian Chabot and Chris Stolte on the Art of Analytics

Tableau Keynote 2014

DataViz: Squaring the Pie Chart (Waffle Charts)

Readers:

Robert-Kosara-Tableau-Software-200x200In the past, I would have highly condemned pie charts without giving you much explanation why. However, Dr. Robert Kosara (photo, left), posted a great thought study of pie charts on his wonderful blog, EagerEyes.org, that I want to share with you.

Dr. Kosara is a Visual Analytics Researcher at Tableau Software, with a special interest in the communication of, and storytelling with, data. He has a Ph.D. in Computer Science from Vienna University of Technology.

Also, as part of his blog post, Robert offers an alternative way to create pie charts: using waffle charts or square pie charts.

Dr. Kosara is also one of the great minds behind Tableau’s new storytelling feature. I hope you enjoy his creative thoughts as much as I do.

Best Regards,

Michael

The Pie Chart

Dr. Kosara contends that pie charts are perhaps the most ubiquitous chart type; they can be found in newspapers, business reports, and many other places. But few people actually understand the function of the pie chart and how to use it properly. In addition to issues stemming from using too many categories, the biggest problem is getting the basic premise: that the pie slices sum up to a meaningful whole.

Touchstone Energy Corporation Pie Chart
Robert points out that the circle (the “pie”) represents some kind of whole, which is made up of the slicesWhat this means is that the pie chart first and foremost represents the size relationship between the parts and the entire thing. If a company has five divisions, and the pie chart shows profits per division, the sum of all the slices/divisions is the total profits of the company.

Five Slices

 

If the parts do not sum up to a meaningful whole, they cannot be represented in a pie chart, period. It makes no sense to show five different occupations in a pie chart, because there are obviously many missing. The total of such a subsample is not meaningful, and neither is the comparison of each individual value to the artificial whole.

Slices have to be mutually exclusive; by definition, they cannot overlap. The data therefore must not only sum up to a meaningful whole, but the values need to be categorized in such a way that they are not counted several times. A good indicator of something being wrong is when the percentages do not sum up to 100%, like in the infamous Fox News pie chart.

The Infamous Fox News Pie Chart

Fox News Pie Chart

In the pie chart above, people were asked which potential candidates they viewed favorably, but they could name more than one. The categories are thus not mutually exclusive, and the chart makes no sense. At the very least, they would need to show the amount of overlap between any two (and also all three) candidates. Though given the size of the numbers and the margin of error in this data, the chart is entirely meaningless.

When to Use Pie Charts

Dr. Kosara points out that there are some simple criteria that you can use to determine whether a pie chart is the right choice for your data.

  • Do the parts make up a meaningful whole? If not, use a different chart. Only use a pie chart if you can define the entire set in a way that makes sense to the viewer.
  • Are the parts mutually exclusive? If there is overlap between the parts, use a different chart.
  • Do you want to compare the parts to each other or the parts to the whole? If the main purpose is to compare between the parts, use a different chart. The main purpose of the pie chart is to show part-whole relationships.
  • How many parts do you have? If there are more than five to seven, use a different chart. Pie charts with lots of slices (or slices of very different size) are hard to read.

In all other cases, do not use a pie chart. The pie chart is the wrong chart type to use as a default; the bar chart is a much better choice for that. Using a pie chart requires a lot more thought, care, and awareness of its limitations than most other charts.

Alternative: Squaring the Pie

A little-known alternative to the round pie chart is the square pie or waffle chart. It consists of a square that is divided into 10×10 cells, making it possible to read values precisely down to a single percent. Depending on how the areas are laid out (as square as possible seems to be the best idea), it is very easy to compare parts to the whole. The example below is from a redesign Dr. Kosara did a while ago about women and girls in IT and computing-related fields.

Kosara Square Pie

Links to Examples of Waffle Charts

I did a little Googling and found a few great examples of Waffle Charts. I have provided links to examples in Tableau, jQuery R and Excel.

Squaring The Pie

Sources:

Jock Mackinlay and Tableau’s Research Team is Building Tomorrow’s UX for Data

Readers:

I thought I would present some interesting information visualization research being conducted at Tableau Software by Jock Mackinlay (photo, right) and his research team.Jock Mackinlay. Source: Tableau Software

Mr. Mackinlay is an information visualization expert and Vice President of Visual Analysis at Tableau Software. With Stuart K. Card, George G. Robertson and others he invented a number of Information Visualization techniques. [1] Mr. Mackinlay, joined Tableau in 2004 after 18 years specializing in data visualization at Xerox PARC.

Tableau Software was born of academic research, and as the company continues to grow, it is building an R&D division to help build a pipeline of innovation. Jock, who heads up the research team, explains how it works and what his team is working on.

I cite references (most of this blog post is based on Derrick Harris’ interview with Mr. Mackinlay in Gigaom) after this blog post for those of you who want to delve deeper into what Jock’s team is doing.

Best regards,

Michael

Tableau Software and Their Research Culture

Tableau LogoTableau Software is many things: a fast-growing thorn in the side of legacy analytics vendorsstock-market gold and the poster child for the next generation of user-friendly data analysis, among them. It’s also a company with a deeply rooted and growing research culture that’s responsible for nearly everything users see when they open its popular visualization application. [2]

Tableau itself is the product of a Stanford Ph.D. dissertation by co-founder and Chief Development Officer Chris Stolte, in conjunction with his then-professor and eventual co-founder Pat Hanrahan. Their project, called Polaris, combined a structured query language with a declarative language for describing data visualization. When they commercialized the research by founding Tableau, that combination – which came together into a technology called VizQL – became the defining feature of the drag-and-drop Tableau experience.

However, the true value of what Stolte and Hanrahan created wasn’t just that let it let mainstream users query data visually and generate graphs, said Mackinlay. There had been a lot of research around ideal ways to visualize data — including his own — but they often focused on customized views of a single problem or type of analysis.“The real power [of Tableau] was to go through a bunch of different views to answer one question,” Mackinlay said. “All you have to be an expert at is your data and the questions you want to ask of it.”

The new research division within Tableau (technically, it was really created about a year and a half ago) is trying to imagine and create the next set of technologies that change the way data analysis is done. The five-person team, which Mackinlay heads, consists of four visualization experts (including Mackinlay), a couple of whom are also specialize in statistics and one of whom specializes in high-performance computing. The fifth member specializes in natural-language processing and computer graphics.

Like most research divisions, the team writes academic papers and works on some projects that might not be applicable for years, but Mackinlay made it pretty clear that the researchers expect everything they’re doing could be commercialized. If there was one thing that separated the famous Bell Labs from Xerox PARC or even Microsoft Research, it’s that Bell was really good at doing really good research that made its way into products, he said. Good research labs need to find the middle ground between nearsighted product upgrades and pie-in-the-sky ideas and, he explained, “You have to have absolutely no gap between the research scientists … and the people who are actually doing the work.”

A still image of an interactive Story Points slideshow. Source: Tableau Public user Matt Francis

Research Leads to Tableau Story Points Feature

Robert-Kosara-Tableau-Software-200x200It’s at a much, much smaller scale than Bell Labs, but Mackinlay thinks Tableau is following down that right path. For example, he said, the Story Points feature in the latest release of the company’s software, allows users to create data slideshows, was the result of tight work between the product team and researcher Robert Kosara (photo, right), who had been doing research into this area for years. As data volumes, dataset complexity and user sophistication all increase, Mackinlay said systems-level research into data processing (including how to optimize for increased client-side computing power) has and will continue to help deliver a smooth user experience.He’s understandably less forthcoming about what, specifically, we can expect to see from Tableau in the near term, but Mackinlay did discuss a few areas of interest. One is making it easier to use aesthetically pleasing icons rather than text labels in charts, an area where he and colleague Vidya Setlur (the aforementioned NLP and graphics specialist) recently published a paper. He’s also interested in text analysis and NLP, and generally adding new types of visualizations — some of which those types of analysis will help enable. For example, “node-link diagrams” (aka graphswill happen, he said, although he can’t put an exact data on when.icons

Mackinlay also suggested that Tableau might expand beyond its current product lineup, which is essentially the same software delivered via the desktop (free and paid), server or cloud. “We can make our existing products easy to use,” Mackinlay said. “We can also make new products that are easy to use — perhaps radically easier than our existing products.”

Although the word “easy” is kind of a misnomer, it’s one that’s used to describe Tableau and other user-friendly software quite often. “Easy” connotes shallowness, Mackinlay said, making an analogy to the evolution of the telephone. Phones have evolved a great deal from those where users just rang the operator, to rotary phones, and now to modern smartphones. With every iteration, manufacturers had to strike the right balance maintaining a recognizable experience but also adding more capabilities.

“We use the two words ‘simple’ and ‘useful,’” he said. “… If you don’t make sure you’re useful, people just aren’t going to stick with you.”

—————————————————————————–

References

[1]  Jock D. Mackinlay, Wikipedia.com, http://en.wikipedia.org/wiki/Jock_D._Mackinlay.

[2] Derrick Harris, A tiny research team at tableau is building tomorrow’s UX for data, Gigaom, July 7, 2014, http://gigaom.com/2014/07/07/a-tiny-research-team-at-tableau-is-building-tomorrows-ux-for-data/.

Small Multiples, Tableau and Ben Jones

Readers:

My BI world is changing a bit as I move more towards using Cognos and Tableau at work. In particular, I have a lot of status reports and dashboards to create for my leadership and I have been doing these mostly in Tableau.

I had a situation recently where I wanted to create a small multiples chart versus using a 3D Bar Chart that already existed. I have created small multiples charts fairly easily in Ben JonesMicroStrategy in my previous work, but have never created one before in Tableau. I reached out to Ben Jones (photo, right) at Tableau. I have been a big fan of Ben’s DataRemixed blog for quite some time and have blogged about Ben many times in the past. Ben was gracious enough to create a simple example small multiples chart for me to use to accomplish what I wanted to visualize. I was really impressed that Ben and Tableau did not put me through any red tape for him to help me. He saw I had a need and he helped me.

Much thanks to Ben for his help and I hope this example is useful to you.

Best Regards,

Michael

Small Multiples

Edward TufteA small multiple (sometimes called trellis chart, lattice chart, grid chart, or panel chart) is a series or grid of small similar graphics or charts, allowing them to be easily compared. The term was popularized by data visualization pioneer, Edward Tufte.

According to Tufte (Envisioning Information, p. 67):

At the heart of quantitative reasoning is a single question: Compared to what? Small multiple designs, multivariate and data bountiful, answer directly by visually enforcing comparisons of changes, of the differences among objects, of the scope of alternatives. For a wide range of problems in data presentation, small multiples are the best design solution.

A Small Multiples Example by Andrew Gelman

One of the most well-known examples of the use of small multiples is Andrew Gelman’s analysis of public support for vouchers, broken down by religion/ethnicity, income, and state (see image below).

GelmanMr. Gelman is a professor of statistics and political science and director of the Applied Statistics Center at Columbia University. His books include Bayesian Data Analysis (with John Carlin, Hal Stern, David Dunson, Aki Vehtari, and Don Rubin), Teaching Statistics: A Bag of Tricks (with Deb Nolan), Data Analysis Using Regression and Multilevel/Hierarchical Models (with Jennifer Hill), Red State, Blue State, Rich State, Poor State: Why Americans Vote the Way They Do (with David Park, Boris Shor, and Jeronimo Cortina), and A Quantitative Tour of the Social Sciences (co-edited with Jeronimo Cortina).

Andrew has done research on a wide range of topics, including: why it is rational to vote; why campaign polls are so variable when elections are so predictable; why redistricting is good for democracy; reversals of death sentences; police stops in New York City, the statistical challenges of estimating small effects; the probability that your vote will be decisive; seats and votes in Congress; social network structure; arsenic in Bangladesh; radon in your basement; toxicology; medical imaging; and methods in surveys, experimental design, statistical inference, computation, and graphics.

[Click on Image to Enlarge]

Gelman Voucher Map Using Small Multiples

My Small Multiples Chart

Since I cannot show you what I used the small multiples chart for related to my job, I made an illustrative, simple example related to home sales in different regions for the past six months. Below is an example of my chart, which I created using Tableau.

[Click on Image to Enlarge]

Home Sales Small Multiples

Adding Trend Lines

One of the key features I wanted to use in my chart was to be able to show trend lines for each small multiple.

However, when I clicked on Trend Lines -> Show Trend Lines, I kept getting the following error message:

Trend Lines Error Message Panel

Ben pointed out that in my original chart, the Columns shelf, Month needed to be a Continuous data type (green pill) rather than a Discrete data type (blue pill).  If you click in the Month pill, you should be able to select “Change to Continuous” and then you should be able to add a trend line. This occurs because you can only calculate a trend line when two axes are involved. The way I had it set up, the Columns were just different categories or attributes, rather than continuous measures.

I thought this would be a nice tip to pass along.

I hope to be able to share more Tableau tips as I become more proficient with the tool.

Bryan’s BI Blog: MicroStrategy vs Tableau

Readers:

Bryan BrandowBryan Brandow, has posted his second new post on his new blog, Bryan’s BI Blog and it is a doozy. Bryan does an in-depth comparison of MicroStrategy vs. Tableau.

Here is a link to the MicroStrategy vs. Tableau post.

Best Regards,

Michael

 

An Introduction to Data Blending – Part 6 (Data Blending using MicroStrategy)

Readers:

In Part 5 of this series on data blending, we reviewed Tableau’s Data Blending Architecture. With Part 5, I have wrapped up the Tableau portion of this series.

I am now going to post, over the next week or so, several parts discussing how we do data blending using MicroStrategy. Fortunately, MicroStrategy just publish a nice technical note on their Knowledgebase (TN Key: 46940) [1] discussing this. Most of what I am sharing today is derived from that technical note.

I probably will have 2-4 parts for this topic in my Data Blending series including how the MicroStrategy Analytical Engine deals with multiple datasets.

I want to thank Kristi Morton (et al) for the wonderful research paper she wrote at The University of Washington [2]. It helped me provide some real insight into the topic and mechanics of data blending, particularly with Tableau. You can learn more about Ms. Morton’s research as well as other resources used to create this blog post by referring to the References at the end of the blog post.

So let’s now dig into how MicroStrategy provides us data blending capabilities.

Best Regards,

Michael

Data Blending using MicroStrategy

In Part 6, we will begin examining using data blending in MicroStrategy. We will first look at how to use attributes from multiple datasets in the same Visual Insight dashboard and link them to existing attributes using the Data Blend feature in MicroStrategy Analytics Enterprise Web 9.4.1.

Prior to v9.4.1 of MicroStrategy, data blending was referred to as Cube Joining.

In MicroStrategy Analytics Enterprise Web 9.4.1, the new Report Services Documents Engine automatically links common attributes using the modeled schema whenever possible. The manual linking is not allowed between different modeled attributes. Just in case the requirement needs to link different attributes, this can be done by using MicroStrategy Architect at the schema level. The join behavior by default for linking related attributes is done using a full outer join. In case there is no relationship between the attributes, then a cross join is used.

The manual attribute linking can be done as shown in the images below.

Part 6 - 1

 

2. Browse the file to match the existing data and select Continue.

Part 6 - 2

 

3. Set the attribute forms if needed. MicroStrategy will automatically assign the detected ones.

Part 6 - 3

4. The attributes can be mapped manually by selecting Link to Project Attribute.

Part 6 - 4

5. Select the attribute form that matches the desired join:

Part 6 - 5

6. The attribute should appear similar to the ones existing in the schema as shown below.

Part 6 - 6

 

7. Save the recently created dataset.

Part 6 - 7

8. Now there are two cubes used as datasets in the same Visual Insight dashboard, as shown below.

Part 6 - 7a

Automatic Linking

The attributes icons now have a blue link, as shown below. This indicates that MicroStrategy has automatically linked them to elements in the Information dataset.

Part 6 - 8

Next: How Data Blending Affects the Analytical Engine’s Behavior in MicroStrategy

———————————————————————————-

References:

[1] MicroStrategy Knowledgebase, How to use attributes from multiple datasets in the same Visual Insight dashboard and link them to existing attributes using the Data Blend feature in MicroStrategy Analytics Enterprise Web 9.4.1, TN Key: 46940, 04/24/2014, https://resource.microstrategy.com/support/mainsearch.aspx.

NOTE: You may need to register to view MiroStrategy’s Knowledgebase.

[2] Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau, University of Washington and Tableau Software, Seattle, Washington, March 2012, http://homes.cs.washington.edu/~kmorton/modi221-mortonA.pdf.

An Introduction to Data Blending – Part 5 (Tableau’s Data Blending Architecture)

Readers:

In Part 4 of this series on data blending, we reviewed Tableau’s Data Blending Principles. We also reviewed an example of data blending in Jonathan Drummey’s Patient Falls Dashboard. [3]

Today, in Part 5 of this series, we will peel the onion a bit more and look at Tableau’s Data Blending Architecture.

Again, much of Parts 1 – 5 are based on a research paper written by Kristi Morton from The University of Washington (and others) [1].

You can learn more about Ms. Morton’s research as well as other resources used to create this blog post by referring to the References at the end of the blog post.

Best Regards,

Michael

Integrating Data in Tableau

In Part 5, we discuss in greater detail how data blending works. Then we discuss how a user builds visualizations using data blending using several large datasets involving airline statistics.

Data Blending Architecture

Part 5 - Figure 1

The data blending system, shown in Figure 1 above, takes as input the VizQL query workload generated by the user’s GUI actions and data source schemas, and automatically infers how to query the data sources remotely and combine their results on-the-fly. The system features a two-tier mediator-based architecture in which the VizQL query workload is analyzed and partitioned at runtime based on the corresponding data source fields being used. The primary mediator initiates this process by removing the visual encodings from the VizQL query workload to yield an abstract query. The abstract query is partitioned for further processing by the primary mediator and one or more secondary mediators. The primary mediator creates the mediated schema for the given query workload. It then federates the abstract queries to the primary data source as well as the secondary mediators and their respective data sources. The wrappers compile the abstract queries into concrete SQL or MDX queries and instantiate the semantic mappings between the data sources and the mediated schema for each query. The primary mediator joins all the result sets returned from all data sources to produce the mediated result set used by the rendering system. [1]

Part 5 - Figure 2

Post-aggregate Join

A visualization is organized by its discrete fields into pages, partitions, colors, etc., and like a GROUP BY clause in SQL, these grouping fields comprise the primary key of the visualization. In a blended visualization, the grouping fields from the primary data source become the primary key of the mediated schema. In Figure 2 above, these are shown as the dark-green fields in the primary data source, and the light green fields represent the aggregated data. Each secondary data source must contain at least one field that matches a visualization grouping field in order to blend into the mediated schema. The matching fields in a secondary data source comprise its join key, and fields appear in the GROUP BY clause issued by the secondary mediator wrappers. The aggregated data from the secondary data source, shown in light-purple, is then left-joined along its join key into the mediated result set. Morton (et al) refer to this left-join of aggregated result sets as a post-aggregate join. [1]

Primary Key Cardinality

many mapping between the domain values of the primary key and those of the secondary join key, because the secondary join key is a subset of the primary key and contains only unique values in the aggregated secondary result set. Morton (et al) find that this approach is the most natural for augmenting a visualization with secondary data sources of uncertain value or quality, which is a common scenario for Tableau users.

Data blending supports many-to-one relationships between the primary and each secondary. This can occur when the secondary data source contains coarser-grained data than the mediated result set, as discussed in Part 3 of this series.

Since the join key in a secondary result set may match a subset of the blended result set primary key, portions of the secondary result set may be duplicated across repeated values in the mediated result set. This does not pose risk of double-counting measure values, becaused all aggregation is performed prior to the join. When a blended visualization uses multiple secondary data sources, each secondary join key may match any subset of the primary key. The primary mediator handles duplicating each secondary result set as needed to join with the mediated result set.

Finally, a secondary dimension which is not part of the join key (and thus not a grouping field in the secondary query) can still be used in the visualization. If it is functionally dependent on the join key, a secondary dimension can be used without affecting the result set cardinality. Tableau references this kind of non-grouping dimension using both MIN and MAX aggregations in the query issued to the secondary data source, which allows Tableau to determine if the dimension is functionally dependent on the join key. For each row in the secondary result set, if the two aggregated values are the same then the value is used as-is, reflecting the functional dependence on the grouping fields. If the aggregated values differ, Tableau represents the value using a special form of NULL called ManyValues. This is represented in the visualization as a ‘*’, but retains the behavior of NULL
when used in calculated fields or other computations. The visual feedback allows a user to distinguish this lack of data from the NULLs which occur due to missing or mismatched data.

Inferring Join Keys

Tableau uses very simple rules for automatically detecting candidate join keys:

  1. The secondary data source field name must match a field with the same name in the primary data source.
  2. The data types must match
  3. If they are date/time fields, they must represent the same granularity date bin in the date/time hierarchy, e.g. both are MONTH. A user can intervene to force a match either by providing field captions to rename fields within the Tableau data model, or by explicitly defining a link between fields using a simple user interface.

Part 5 - Figure 3

Another Simple Blending Example

A Tableau data blending scenario is shown in Figure 3 above, which includes multiple views that were composed in minutes by uniquely mashing up four different airline datasets, the largest of which include a 324 million row ticket pricing database and a 140 million row on-time performance database. A user starts by dragging fields from any dataset on to a blank visual canvas, iteratively building a VizQL statement which ultimately produces a visualization. In this example, the user first drags the VizQL fields, YEAR(Flight Date) and AVG(Airfare), from the pricing dataset onto the visual canvas.

Data blending occurs when the user adds fields from a separate dataset to an existing VizQL statement in order to augment their analysis. Tableau assigns the existing dataset to the primary mediator and uses secondary mediators to manage each subsequent dataset added to the VizQL. The mediated schema has a primary key composed of the grouping VizQL fields from the primary dataset (e.g. YEAR(Flight Date)); the remaining fields in the mediated schema are the aggregated VizQL fields from the primary dataset along with the VizQL fields from each secondary dataset.

Continuing our example, the user wishes to drag AVG(Total Cost per Gallon) from the fuel cost dataset to the visualization. The schema matching algorithm examines
the secondary dataset for one or more fields whose name exactly matches a field in the primary key of the mediated schema. While the proposed matches are often sufficient and acceptable, the user can specify an override. Since the fuel cost dataset has a field named Date, the user provides a caption of Flight Date to resolve the schema discrepancy. At this point the mediated schema is created and the VizQL workload is then federated to the wrappers for each dataset. Each wrapper compiles VizQL to SQL or MDX for the given workload, executes the query, and maps the result set into the intermediate form expected by the primary mediator.

The mapping is performed dynamically, since both the VizQL and the data model evolve during a user’s iterative analytical workflow. Finally, the primary mediator
performs a left-join of each secondary result set along the primary key of the mediated schema. In this example, the mediated result set is rendered to produce the visualization shown in Figure 3(a).

Evolved Blending Example

Figure 3(b) above shows further evolution of the analysis of airline datasets, and demonstrates several key points of data blending. First, the user adds a unique ID field named unique carrier from the primary dataset to the VizQL to visualize results for each airline ID over time. The mediated schema adapts by adding this field to its primary key, and the secondary mediator automatically queries the fuel cost dataset at this finer granularity since it too has a field named uniquecarrier. Next, the user decorates the visualization with descriptive airline names for each airline ID by dragging a field named Carrier Name from a lookup table.

This dataset is at a coarser granularity than the existing mediated schema, since it does not represent changes to the carrier name over time. Morton’s (et al) system automatically handles this challenge by allowing the left-join to use a subset of the mediated result set primary key, and replicating the carrier name across the mediated result set. Figure 4 below demonstrates this effect using a tabular view of a portion of the mediated result set, along with portions of the primary and secondary result sets.

The figure also demonstrates how the left-join preserves data for years which have no fuel cost records. Last, the user adds average airline delays from a 140 million row dataset which matches on Flight Date and uniquecarrier. This is a fast operation, since the wrapper performs mapping operations on the relatively small, aggregated result set produced by the remote database. Note that none of these additional analytical tasks required the user to intervene in data integration tasks, allowing their focus to remain on finding insight in the data.

Part 5 - Figure 4

Filtering

Tableau provides several options for filtering data. Data may be filtered based on aggregate conditions, such as excluding including airlines having a low total count of flights. A user can filter aggregate data from the primary and secondary data sources in this fashion, which results in rows being removed from the mediated result set. In contrast, row level filters are only allowed for the primary data source. To improve performance of queries sent to the secondary data sources, Tableau will filter the join keys to exclude values which are not present in the domain of the primary data source result set, since these values would be discarded by the left-join.

Data Cleaning Capabilities

As mentioned in the Inferring Join Keys section above, Tableau supports user intervention in resolving field names when schema matching fails. And once the schemas match and data is blended, the visualization can help provide feedback regarding the validity of the underlying data values and domains. If there are any data inconsistencies, users can provide aliases for a field’s data values which will override the original values in any query results involving that field. The primary mediator performs a left-join using the aliases of the data values, allowing users to blend data despite discrepancies from data entry errors and spelling variations. Tableau provides a simple user interface for editing field aliases. Calculated fields are another aspect of Tableau’s data model which support data cleaning. Calculated fields support arbitrary transformations of original data values into new data values, such as trimming whitespace from a string or constructing a date from an epoch-based integer timestamp.

As with database fields, calculated fields can be used as primary keys or join keys.

Finally, Tableau allows users to organize a field’s related data values into groups. These ad-hoc groups can be used for entity resolution, such as binding multiple variations of business names to a canonical form. Ad-hoc groups also allow constructing coarser-grained structures, such as grouping states into regions. Data blending supports joins between two ad-hoc groups, as well as joins between an ad-hoc group and a string field.

Next: Data Blending Using MicroStrategy

———————————————————————————-

References:

[1] Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau, University of Washington and Tableau Software, Seattle, Washington, March 2012, http://homes.cs.washington.edu/~kmorton/modi221-mortonA.pdf.

[2] Hans Rosling, Wealth & Health of Nations, Gapminder.org, http://www.gapminder.org/world/.

[3] Jonathan Drummey, Tableau Data Blending, Sparse Data, Multiple Levels of Granularity, and Improvements in Version 8, Drawing with Numbers, March 11, 2013, http://drawingwithnumbers.artisart.org/tableau-data-blending-sparse-data-multiple-levels-of-granularity-and-improvements-in-version-8/.

 

An Introduction to Data Blending – Part 4 (Data Blending Design Principles)

Readers:

In Part 3 of this series on data blending, we  examining the benefits of blending data. We also reviewed an example of data blending that illustrated the possible outcomes of an election for the District 2 Supervisor of San Francisco.

Today, in Part 4 of this series, we will discuss data blending design principles and show another illustrative example of data blending using Tableau.

Again, much of Parts 1, 2, 3 and 4 are based on a research paper written by Kristi Morton from The University of Washington (and others) [1].

You can learn more about Ms. Morton’s research as well as other resources used to create this blog post by referring to the References at the end of the blog post.

Best Regards,

Michael

Data Blending Design Principles

In Part 3, we describe the primary design principles upon which Tableau’s data blending feature was based. These principles were influenced by the application needs of Tableau’s end-user. In particular, we designed the blending system to be able to integrate datasets on-the-fly, be responsive to change, and driven by the visualization. Additionally, we assumed that the user may not know exactly what she is looking for initially, and needs a flexible, interactive system that can handle exploratory visual analysis.

Push Computation to Data and Minimize Data Movement

Tableau’s approach to data visualization allows users to leverage the power of a fast database system. Tableau’s VizQL algebra is a declarative language for succinctly describing visual representations of data and analytics operations on the data. Tableau compiles the VizQL declarative formalism representing a visual specification into SQL or MDX and pushes this computation close to the data, where the fast database system handles computationally intensive aggregation and filtering operations. In response, the database provides a relatively small result set for Tableau to render. This is an important factor in Tableau’s choice of post-aggregate data integration across disparate data sources – since the integrated result sets must represent a cognitively manageable amount of information, the data integration process operates on small amounts of aggregated, filtered data from each data source. This approach avoids the costly migration effort to collocate massive data sets in a single warehouse, and continues to leverage fast databases for performing expensive queries close to the data.

Automate as Much as Possible, but Keep User in Loop

Tableau’s primary focus has been on ease of use since most of Tableau’s end-users are not database experts, but range from a variety of domains and disciplines: business analysts, journalists, scientists, students, etc. This lead them to take a simple, pay-as-you-go integration approach in which the user invests minimal upfront effort or time to receive the benefits of the system. For example, the data blending system does not require the user to specify schemas for their data sets, rather the system tries to infer this information as well as how to apply schema matching techniques to blend them for a given visualization. Furthermore, the system provides a simple drag-and-drop interface for the user to specify the fields for a visualization, and if there are fields from multiple data sources in play at the  same time, the blending system infers how to join them to satisfy the needs of the visualization.

In the case that something goes wrong, for example, if the schema matching could not succeed, the blending system provides a simple interface for specifying data source relationships and how blending should proceed. Additionally, the system provides several techniques for managing the impact of dirty data on blending, which we discuss in more in Part 5 of this series.

Another Example: Patient Falls Dashboard [3]

NOTE: The following example is from Jonathan Drummey via the Drawing with Numbers blog site. The example uses Tableau v7, but at the end of the instructions on how he creates this dashboard in Tableau v7, Mr. Drummey includes instructions how the steps became more simplied in Tableau v8. I have included a reference to this blog post on his site in the reference section of my blog entry. The “I”, “me” voice you read in this example is that of Mr. Drummey.

As part of improving patient safety, we track all patient falls in our healthcare system, and the number of patient days – the total of the number of days of inpatient stays at the hospital. Every month report we report to the state our “fall rate,” a metric of the number of falls with injury for certain units in the hospital per 1000 patient days, i.e. days that patients are at the hospital. Our annualized target is to have less than 0.7 falls with injury per 1000 patient days.

A goal for our internal dashboard is to show the last 13 months of fall rates as a line chart, with the most recent fall events as a bar chart, in a combined chart, along with a separate text table showing some details of each fall event. Here’s the desired chart, with mocked-up data:

 

combo bars and lines

On the surface, blending this data seems really straightforward. We generate a falls rate very month for every reporting unit, so use that as the primary, then blend in the falls as they happen. However, this has the following issues:

  • Sparse Data – As I’m writing this, it’s March 7th. We usually don’t get the denominator of the patient days for the prior month (February) for a few more days yet, so there won’t be any February row of measure data to use as the primary to get the February fall events to show on the dashboard. In addition, there still wouldn’t be any March data to get the March fall events. Sometimes when working with blend, the solution is to flip our choices for the primary and secondary datasource. However, that doesn’t work either because a unit might go for months or years without a patient fall, so there wouldn’t be any fall events to blend in the measure data.
  • Falls With and Without Injury – In the bar chart, we don’t just want to show the number of patient falls, we want to break down the falls by whether or not they were falls with injury – the numerator for the fall rate metric – and all other falls. The goal of displaying that data is to help the user keep in mind that as important as it is to reduce the number of falls with injury, we also need to keep the overall number of falls down as well. No fall = no chance of fall with injury.
  • Unit Level of Detail – Because the blend needs to work at the per-unit level of detail as well as across all reporting units, that means (in version 7 at least) that the Unit needs to be in the view for the blend to work. But we want to display a single falls rate no matter how many units are selected.

Sparse Data

To deal with issue of sparse data, there are a few possible solutions:

  • Change the combined line and bar chart into separate charts. This would perhaps be the easiest, though it would require some messing about with filters, hidden reference lines, and continuous date axes to ensure that the two charts had similar axis ranges no matter what. However, that would miss out on the key capability of the combined chart to directly see how a fall contributes to the fall rate. In addition, there would be no reason to write this blog post. :)
  • Perform padding in the data source, either via a query/view or Custom SQL. In an earlier version of this project I’d built this, and maintaining a bunch of queries with Cartesian joins isn’t my favorite cup of tea.
  • Building a scaffold data source with all combinations of the month and unit and using the scaffold as the primary data source. While possible, this introduces maintenance issues when there’s a need for additional fields at a finer level of detail. For example, the falls measure actually has three separate fall rates – monthly, quarterly, and annual. These are generated as separate rows in our measures data and the particular duration is indicated by the Period field. So the scaffold source would have to include the Period field to get the data, but then that could be too much detail for the blended fall event data, and make for more complexity in the calculations to make sure the aggregations worked properly.
  • Do a tiny bit of padding in the query, then do the rest in Tableau via Show Missing Values aka domain padding. As I’d noted in an earlier post on blending, domain padding occurs before data is blended so we can pad out the measure data through the current date and then include all the falls. This is the technique I chose, for the reason that padding one row to the data is trivial and turning on Show Missing Values is a couple of mouse clicks. Here’s how I did that:

In my case, the primary data source is a Microsoft Access query that gets the falls measure results from a table that also holds results for hundreds of other metrics that we track. I created a second query with the same number of columns that returns Null for every field except the Measure Date, which has a value of 1/1/1900. Then a third query UNION’s those two queries together, and that’s what is used as the data source in Tableau.

Then, in Tableau, I added a calculated field called Date with the following formula:

//used for padding out display to today
IF [Measure Date] == #1/1/1900# THEN 
    TODAY() 
ELSE 
    [Measure Date] 
END

The measure results data contains a row per measure, reporting unit, and the period. These are pre-calculated because the data is used in a variety of different outputs. Since in this dashboard we are combining the results across units, we can’t just use the rate, we need to go back to the original numerator and denominator. So, I also created a new field for the Calculated Rate:

SUM([Numerator])/SUM([Denominator])

Now it’s possible to start building the line chart view:

  1. Put the Month(Date) – the full month/year version as a discrete – on Columns, Calculated Rate on Rows, Period on the Color Shelf. This only shows the data that exists in the data source, including the empty value for the current month (March in this case):

 

Screen Shot 2013-03-09 at 1.11.25 PM

 

  1. Turn on Show Missing Values for Month(Date) to start domain padding. Now we can see the additional column(s) for the month(s) – February in this case between January to the current month that Tableau has added in:

 

Screen Shot 2013-03-09 at 1.14.19 PM

 

With a continuous (green pill) date, this particular set-up won’t work in version 8. Tableau’s domain padding is not triggered when the last value of the measure is Null. I’m hoping this is just an issue with the beta, I’ll revise this section with an update once I find out what’s going on.

Even though the measure data only has end of month dates, instead of using Exact Date for the month I used Month(Date) because of two combined factors: One is that the default import of most date fields from MS Jet sources turns them into DateTime fields, the second is that Show Missing Values won’t work on an Exact Date for a DateTime field, you have to assign an aggregation to a DateTime (even Second will work). This is because domain padding at this level can create an immense number of new rows and cause Tableau to run out of memory, so Tableau keeps the option off unless you want it. Also note that you can turn on Show Missing Values for an Exact Date for a Date Field.

  1. Now for some cleanup steps: for the purposes of this dashboard, filter Period to remove Monthly (we do quarterly reporting), but leave in Null because that’s needed for the domain padding.
  2. Right-click Null on the Color Legend and Hide it. Again, we don’t exclude this because this would cause the extra row for the domain padding to fail.
  3. Set up a relative date filter on the Date field for the last 13 months. This filter works just fine with the domain padding.

Filtering on Unit

Here’s a complicating factor: If we add a filter on Unit, there’s a Null listed here:

 

Screen Shot 2013-03-09 at 1.18.31 PM

I’d just want to see the list of units. But if we filter that Null out, then we lose the domain padding, the last date is now January 2013:

 

Screen Shot 2013-03-09 at 1.18.58 PM

 

One solution here would be to alter the padding to add a padding row for every unit, instead of just one unit. Since Tableau doesn’t let us just hide elements in a filter, and we actually have more reporting units in our data than we are displaying on the dashboards, I chose to use a parameter filter because there are more reporting units in our production data than we are displaying on the dashboards, yet the all-unit rate needs to include all of the data. Setting this up included a parameter with All and each of the units, and a calculated field called “Chosen Unit Filter” with the following formula, that is set to Filter on False:

[Choose Unit] == "All" OR [Choose Unit] == [Unit]

Falls With and Without Injury

In a fantasy world, to create the desired stacked bars I’d be able to drag the Number of Records from the secondary datasource, i.e. the number of fall events, drag an Injury indicator onto the Color Shelf, and be done. However, that runs into the issue of having a finer level of detail in the secondary than in the primary, which I’ll walk through solutions for in the next section. In this case, since there are only two different numbers, the easy way is to generate two separate measures, then use Measure Names/Measure Values to create the stacked bars – Measure Values on Rows, and Measure Names on the Color Shelf. Here’s the basic calculation for Falls with Injury:

SUM(IF [Injury] != "None" THEN 1 ELSE 0 END)

We’re using a row-level calculated field to generate the measure, and a slightly different calc for Falls w/out Injury.

Unit Level of Detail

When we want to blend in Tableau at a finer level of detail and aggregate to a higher level, historically there have been three options:

  • Don’t use blending at all, instead use a query to perform the “blend” outside of Tableau. In the case that there are totally different data sources, this can be more difficult but not impossible by using one of the systems or a different system to create a federated data source, for example by adding your Oracle table as an ODBC connection to your Excel data, then making the query on that. In this case, we don’t have to do that.
  • Use Tableau’s Primary Groups feature “push” the detail from the secondary into the primary data source. This is a really helpful feature, the one drawback is that it’s not dynamic so any time there are new groupings in the secondary it would have to be re-run. Personally, I prefer automating as much as possible so I tend not to use this technique.
  • Set up the view with the needed dimensions in the view – on the Level of Detail Shelf, for example – and then use table calculations to do the aggregation. This is how I’ve typically built this kind of view.

Tableau version 8 adds a fourth option:

  • Tell Tableau what fields to blend on, then bring in your measures from the secondary.

I’ll walk through the table calculation technique, which works the same in version 7 and version 8, and then how to take advantage of v8′s new feature.

Using Table Calculations to Aggregate Blended Data

In order to blend the the falls data at the hospital unit level to make sure that we’re only showing falls for the selected unit(s), the Unit has to be in the view (on the Rows, Columns, or Pages Shelves, or on the Marks Card). Since we don’t actually need to display the Unit, the Level of Detail Shelf is where we’ll put that dimension. However, just adding that to the view leads to a bar for each unit, for example for April 2012 one unit had one fall with injury and another had two, and two units each had two falls without injury.

 

Screen Shot 2013-03-09 at 1.30.27 PM

 

To control things like tooltips (along with performance in some cases), it’s a lot easier to have a single bar for each month/measure. To do that, we turn to a table calculation, here’s the Falls w/Injury for v7 Blend calculated field, set up in the secondary data source:

IF FIRST()==0 THEN
	TOTAL([Falls w/Injury])
END

This table calculation has a Compute Using of Unit, so it partitions on the Month of Date. The IF FIRST()==0 part ensures that there is only one mark per partition. I’m using the TOTAL() aggregation here because it’s easier to set up and maintain. The alternative is to use WINDOW_SUM(), but in Tableau prior to version 7 there are some performance issues, so the calc would be:

IF FIRST()==0 THEN
	WINDOW_SUM(SUM(Falls w/Injury]), 0, IIF(FIRST()==0,LAST(),0))
END

The ,0 IIF(FIRST()==0,LAST(),0 part is necessary in version 7 to optimize performance, you can get rid of that in version 8.

You can also do a table calculation in the primary that accesses fields in the secondary, however TOTAL() can’t be used across blended data sources, so you’d have to use the WINDOW_SUM version.

With a second table calculation for the Falls w/out Injury, now the view can be built, starting with the line chart from above:

  1. Add Measure Names (from the Primary) to Filters Shelf, filter it for a couple of random measures.
  2. Put Measure Values on the Rows Shelf.
  3. Click on the Measure Values pill on Rows to set the Mark Type to Bar.
  4. Drag Measure Names onto the Color Shelf (for the Measure Values marks).
  5. Drag Unit onto the Level of Detail Shelf (for the Measure Values marks).
  6. Switch to the Secondary to put the two Falls for v7 Blend calcs onto the Measure Values Shelf.
  7. Set their Compute Usings to Unit.
  8. Remove the 2 measures chosen in step 1.
  9. Clean up the view – turn on dual axes, move the secondary axis marks to the back, change the axis tick marks to integers, set axis titles, etc.

This is pretty cool, we’re using domain padding to fill in for non-existent data and then having a blend happening at one level of detail while aggregating to another, just for the second axis. Here’s the v7 workbook on Tableau Public:

Patient Falls Dashboard - Click on Image to go to Tableau Public

Patient Falls Dashboard – Click on image above to go to Tableau Public

Tableau Version 8 Blending – Faster, Easier, Better

For version 8, Tableau made it possible to blend data without requiring the linking fields in the view. Here’s how I build the above v7 view in v8:

  1. Add Measure Names (from the Primary) to Filters Shelf, filter it for a couple of random measures.
  2. Put Measure Values on the Rows Shelf.
  3. Click on the Measure Values pill on Rows to set the Mark Type to Bar.
  4. Drag Measure Names onto the Color Shelf (for the Measure Values marks).
  5. Switch to the Secondary and click the chain link icon next to Unit to turn on blending on Unit.
  6. Drag the Falls w/Injury and Falls w/out Injury calcs onto the Measure Values Shelf.
  7. Remove the 2 measures chosen in step 1.
  8. Clean up the view – turn on dual axes, move the secondary axis marks to the back, change the axis tick marks to integers, set axis titles, etc.

The results will be the same as v7.

Next: Tableau’s Data Blending Architecture

—————————————————————-

References:

[1] Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau, University of Washington and Tableau Software, Seattle, Washington, March 2012, http://homes.cs.washington.edu/~kmorton/modi221-mortonA.pdf.

[2] Hans Rosling, Wealth & Health of Nations, Gapminder.org, http://www.gapminder.org/world/.

[3] Jonathan Drummey, Tableau Data Blending, Sparse Data, Multiple Levels of Granularity, and Improvements in Version 8, Drawing with Numbers, March 11, 2013, http://drawingwithnumbers.artisart.org/tableau-data-blending-sparse-data-multiple-levels-of-granularity-and-improvements-in-version-8/.

 

An Introduction to Data Blending – Part 3 (Benefits of Blending Data)

Readers:

In Part 2 of this series on data blending, we delved deeper into understanding what data blending is. We also examined how data blending is used in Hans Rosling’s well-known Gapminder application.

Today, in Part 3 of this series, we will dig even deeper by examining the benefits of blending data.

Again, much of Parts 1, 2 and 3 are based on a research paper written by Kristi Morton from The University of Washington (and others) [1].

You can learn more about Ms. Morton’s research as well as other resources used to create this blog post by referring to the References at the end of the blog post.

Best Regards,

Michael

Benefits of Blending Data

In this section, we will examine the advantages of using the data blending feature for integrating datasets. Additionally, we will review another illustrative example of data blending using Tableau.

Integrating Data Using Tableau

In Ms. Morton’s research, Tableau was equipped with two ways of integrating data. First, in the case where the data sets are collocated (or can be collocated), Tableau formulates a query that joins them to produce a visualization. However, in the case where the data sets are not collocated (or cannot be collocated), Tableau federates queries to each data source, and creates a dynamic, blended view that consists of the joined result sets of the queries. For the purpose of exploratory visual analytics, Ms. Morton (et al) found that data blending is a complementary technology to the standard collocated approach with the following benefits:

  • Resolves many data granularity problems
  • Resolves collocation problems
  • Adapts to needs of exploratory visual analytics

Figure 1 - Company Tables

Image: Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau. [1]

Resolving Data Granularity Problems

Often times a user wants to combine data that may not be at the same granularity (i.e. they have different primary keys). For example, let’s say that an employee at company A wants to compare the yearly growth of sales to a competitor company B. The dataset for company B (see Figure 1 above) contains a detailed quarterly growth of sales for B (quarter, year is the primary key), while company A’s dataset only includes the yearly sales (year is the primary key). If the employee simply joins these two datasets on yearly earnings, then each row from A will be duplicated for each quarter in B for a given year resulting in an inaccurate overestimate of A’s yearly earnings.

This duplication problem can be avoided if for example, company B’s sales dataset were first aggregated to the level of year, then joined with company A’s dataset. In this case, data blending detects that the data sets are at different granularities by examining their primary keys and notes that in order to join them, the common field is year. In order to join them on year, an aggregation query is issued to company B’s dataset, which returns the sales aggregated up to the yearly level as shown in Figure 1. This result is blended with company A’s dataset to produce the desired visualization of yearly sales for companies A and B.

The blending feature does all of this on-the-fly without user-intervention.

Resolves Collocation Problems

As mentioned in Part 1, managed repository is expensive and untenable. In other cases, the data repository may have rigid structure, as with cubes, to ensure performance, support security or protect data quality. Furthermore, it is often unclear if it is worth the effort of integrating an external data set that has uncertain value. The user may not know until she has started exploring the data if it has enough value to justify spending the time to integrate and load it into her repository.

Thus, one of the paramount benefits of data blending is that it allows the user to quickly start exploring their data, and as they explore the integration happens automatically as a natural part of the analysis cycle.

An interesting final benefit of the blending approach is that it enables users to seamlessly integrate across different types of data (which usually exist in separate repositories) such as relational, cubes, text files, spreadsheets, etc.

Adapts to Needs of Exploratory Visual Analytics

A key benefit of data blending is its flexibility; it gives the user the freedom to view their blended data at different granularities and control how data is integrated on-the-fly. The blended views are dynamically created as the user is visually exploring the datasets. For example, the user can drill-down, roll-up, pivot, or filter any blended view as needed during her exploratory analysis. This feature is useful for data exploration and what-if analysis.

Another Illustrative Example of Data Blending

Figure 2 (below) illustrates the possible outcomes of an election for District 2 Supervisor of San Francisco. With this type of visualization, the user can select different election styles and see how their choice affects the outcome of the election.

What’s interesting from a blending standpoint is that this is an example of a many-to-one relationship between the primary and secondary datasets. This means that the fields being left-joined in by the secondary data sources match multiple rows from the primary dataset and results in these values being duplicated. Thus any subsequent aggregation operations would reflect this duplicate data, resulting in overestimates. The blending feature, however, prevents this scenario from occurring by performing all aggregation prior to duplicating data during the left-join.

Figure 2 - San Francisco Election

Image: Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau. [1]

Next: Data Blending Design Principles

——————————————————————————————————–

References:

[1] Kristi Morton, Ross Bunker, Jock Mackinlay, Robert Morton, and Chris Stolte, Dynamic Workload Driven Data Integration in Tableau, University of Washington and Tableau Software, Seattle, Washington, March 2012, http://homes.cs.washington.edu/~kmorton/modi221-mortonA.pdf.

[2] Hans Rosling, Wealth & Health of Nations, Gapminder.org, http://www.gapminder.org/world/.

Follow

Get every new post delivered to your Inbox.

Join 273 other followers