Power BI is an awesome tool but no tool will be of any use if your underlying data features the 3 “I”s:
For a simple ad-hoc analysis of one source you can get by fixing #1 in Power Query and hoping to identify the “Incorrect” in the analysis. It’s no secret that the initial benefits of many Business Intelligence projects are typically the identification of data issues that become apparent through improved insights with the use of effective data visualisation.
As soon as you want to use multiple sources #3 will become an issue, where “changes in the front end (i.e. Power Query)” will often not fix the issues anymore and you will require a broader BI repository strategy where a key part is the architecture of an integrated data storage approach for analytical purposes often referred to as a “Data Warehouse”.
For us at Managility, the reporting and front end side is typically the easiest part of project that takes 10-20% of the overall implementation time. Typically, the major portion of the rest of the time in our projects is spent on the design and implementation of the back end with loading and cleansing and ensuring consistency of data in between the different sources into a database optimised for analytics.
A process referred to as ETL (Extraction Transformation and Loading) in our tech speak. As much as software vendors will try to position their tool as “really easy” and “self-service” an inherent part of the data integration process are complex issues where data typically “doesn’t match” and mappings andrules will need to be established that no out of the box process will be able to cover co,mpletel and that typically requires specialist knowledge.
At a minimum, we recommend that as soon as you embark on more complex analytics projects with different sources, you make yourself familiar (or find someone to help you…) with multi-dimensional modelling and how to structure data into star schemas (in a nutshell the separation of facts, records of what is happening and dimensions: details and hierarchies by which you want to analyse your data). It is a more or less mandatory concept in Power BI to have data structured that way if you want to analyse across different sources. At minimum, you will require a dimension table with distinct elements by which the different sources and their “Fact Tables” can be joined. The simplest and likely most widely used example there is a common date table which we will cover in more detail in the next tips&tricks post here.