## Data sources

We call 'Data sources' to the data elements we can use and manipulate in the expression builder to create expressions and calculations. These elements act as parameters of the expressions.

- Screen's Widgets: Some widget properties can be used as parameters in your expression. To use them, drag the widgets from the 'Screen' tab of the Expression Builder and drop them in the editing area. Then you may choose one of the following properties:

  - Value: The value displayed by a widget on the current screen. Any widget with text (eg. button) will have this property.

  - Selected value: The current selected value of a selection component (eg. select list).

  - Pos.X relative: The X coordinate of the current widget's position relative to its closest parent container.

  - Pos.X absolute: The X coordinate of the current widget's position relative to the page.

  - Pos.Y relative: The Y coordinate of the current widget's position relative to its closest parent container.

  - Pos.Y absolute: The Y coordinate of the current widget's position relative to the page.

  - Width: The width of the widget in pixels.

  - Height: The height of the widget in pixels.

  - Angle: The rotation angle of the widget in degrees.

  - Is visible: Will be true when the widget is visible and false otherwise.

- Variables: As explained in Variables page, variables act as generic containers for data which can be used in expressions.

- Data Masters: Use a Data Master in a expression to operate with all its records. You can also use Data Masters' attributes in order to filter a Data Master among other functions.