Figure 1: Data Source Connections to Tableau 

Tableau Desktop is data source agnostic. This means you can connect to a host of different types of data sources from Tableau including files (csv, pdf, excel, json) and systems or databases. The data source can be anywhere in the web or contained in a server inside your organisation. In this case, what you need are the credentials and network settings to access those systems and then you can connect to the data from Tableau. 

Figure 2: List of data sources in Tableau Public

Tableau Public does have restrictions on the types of data sources which it can be connected to (some of these can be viewed in Figure 2 above) as well as spatial data and you can also utilise a connection to hosted sources including Google drive and REST APIs.  

In either case, the data connection stream is one-way; you will not be able to change the original source data in Tableau. 

When connecting to data in Tableau Desktop, it is necessary to decide whether the connection should be Live or an Extract. A Live connection creates a direct link between the Tableau workbook and the source so that if the source is updated, the workbook updates simultaneously. Extracts are used to improve the performance of the workbook and subsequent visualisations by capturing the current position of the data and creating a version in memory which does not automatically update (not possible in all connection types).  

Figure 3: Tableau Desktop: Live or Extract connection 

During the data connection process, Tableau will ascertain how each field from your source data should be used, including how granular the contents of that field are, if it contains decimals, if it matches a known reporting role such as date or geography. Depending on this language, fields from the source data will be classified by colour: Blue or Green. Blue fields are discrete, separate categories, like buckets. A good example is anything that is text based, qualitative. Green fields are continuous quantitative values, that can be aggregated by SUM(), AVG() and will be used to create the axis or scale of a plot. These classifications are reflected in the coloured icons above each field in the data connection preview. 

Figure 4: Continuous Values: Whole or Decimal numbers

The above icon in green is an example of one of the icons that are located above each field in the data connection preview. Other examples are Dates (if there is a time component, Date & Time type),  String / text values, Boolean / True False values.

In addition, there are geographic roles which can be detected or assigned manually at the data configuration stage, and all have the same blue geography symbol. These are also discrete. 

It is important to keep in mind that the Blue (discrete) and Green (continuous) state of the data types, as well as the roles assigned, are open for customisation.    

Now, let’s move on to visualisations in Tableau.