Data and Schema

In Draco, you can describe what you know about the dataset and the fields in the data. There can be only one dataset in a Draco program.

Besides general statistics about the whole dataset, the schema has information about field types and field statistics.

You can use Draco’s data schema API to generate a schema description from a file or Pandas dataframe.

Dataset Properties

General properties of the dataset that are not specific to a field are properties of the root.

number_rows : The number of rows in the dataset. Draco can use this fact about the data to recommend chart design that scale to the size of the dataset.

Field Properties

Draco can use information about the field type and field statistics. Each field entity is associated with a field. The facts therefore have the form of e.g. attribute((field,type),foo,number). (read as the type of the foo field is number). For each field, there should be an entity fact entity that tells Draco that the field exists on the root (e.g. entity(field,root,foo).).

(field,name) : The name of the field.

(field,type) : The type of the data in the column for this field. One of number, string, boolean, or datetime.

(field,unique) : The number of unique values.

(field,entropy) : The entropy of the field. (To save a more accurate value, this field entropy value is 1000 times of the actual entropy).

(field,min) : The minimum value. Only used for numbers.

(field,max) : The maximum value. Only used for numbers.

(field,std) : The standard deviation. Only used for numbers.

(field,freq) : The frequency of the most common value. Only used for strings.

(field,interesting) : When the task regards specific fields, fields can be marked as relevant to the task.

Example

attribute(number_rows,root,42).

entity(field,root,f1).
attribute((field,name),f1,date).
attribute((field,type),f1,datetime).
attribute((field,unique),f1,1461).
attribute((field,entropy),f1,7287).
attribute((field,interesting),f1,true).

entity(field,root,f2).
attribute((field,name),f2,precipitation).
attribute((field,type),f2,number).
attribute((field,unique),f2,111).
attribute((field,min),f2,0).
attribute((field,max),f2,55).
attribute((field,std),f2,6).
attribute((field,entropy),f1,2422).

entity(field,root,f3).
attribute((field,name),f3,weather).
attribute((field,type),f3,string).
attribute((field,unique),f3,5).
attribute((field,freq),f3,714).
attribute((field,entropy),f1,1201).