Over the next couple of months I will use this repo to share my learning about using deneb for creating data visualizations inside Power BI. If you are not familiar with deneb you should start here: https://deneb-viz.github.io/

I consider deneb being a very powerful custom data visual available for Power BI. deneb does not provide a certain data visualization to solve a data visualization task instead it provides a framework that allows us creating almost any data visualization we need to communicate insights with the users of our Power BI reports. During the last years I encountered various requirements for specific data visualizations that have not been met by the default visuals or the custom visuals available. Sometimes these requirements could have been described as minor additions to the way information is presented, sometimes these requirements only could be met by creating R or Python script visauls. Sometimes I considered creating a new custom visual. All of these custom approaches have their downsides, no matter how powerful packages like ggplot2 or seaborn are, the data visuals created using this are lacking interactivity the users of Power BI are used to. Creating tailor made custom visuals requires additional tools like Visual Studio Code for developing the custom visual. From my point of view the amazing freedom that comes with creating my own custom visuat that fits the needs exactly comes with a price tag, maintenance and the integration of additional functionality, meaning new features. Next to that, I do not know that many business users that are familiar with the required developent skills.

I consider deneb different, because it provides a framework where I, the report author can focus on the data visualization task without the need for additional tools. When I say deneb provides a framework where almost any data visualization can be created, this of course also states that there are certain tasks that can not be solved. This is true for two reasons. The first reason of course is simple, it's simply because of my lack of knowledge, but this is what this repo is all about sharing my learning experience. The second reason is a more complex one. At the current moment deneb embeds two javascript libraries used for data visualization, vega-lite and vega. There are certain data visualization task that can not be solved with the above mentioned libraries alone, e.g. the mapping of data to spatial aesthetics. But I'm happy about these kind of limitations as there certain capabilities of a custom visual require communicating with third party services, this does not necessarily mean that data is not safe, but this prevents the visual from becoming a certified. From my personal perspective I consider being certified more important than being able to talk with third party services.

deneb allows to describe how the data at hand should be visualized by providing a specifiaction, this specifiaction is using json notification. Then this specifiaction is used for rendering a data visual, that out the box supports cross filter and tooltip capabilities (thanks to the inventer of the deneb custom visual). If you think this is simple, you are correct. Unfortunately, the vega-lite and the vega library provide a lot of means to manipulate the available data, create new data using transforms and expressions. Because, it is required to provide the "formula" in a syntax I'm not familiar with, I'm struggling. I thing what Alberto Ferrari and Marco Russo once have said about DAX is also valid for using vega-lite and vega: Using vega-lite or vega is simple, but not easy.

As I'm convinced that deneb will play a great part when a custom visual is required, I will learn how use it.

Throughout, the next months I will use this repo to share my findings, my projects - the data visualization tasks I'm currently working on.

The next sections will desribe the topology of a specifiation, its sections like mark, encoding, layers, and all the details that have not been from the beginning. This is not about how to use deneb inside Power BI, this is described in very great detail on the official site.