CS 4478/5578 ARFF Details

An ARFF (Attribute-Relation File Format) file is an ASCII text file that describes a machine learning dataset (or relation). It was developed at the University of Waikato (NZ) for use with the Weka machine learning software. We will use a simplifed version for CS 4478/5578.

ARFF files have two distinct sections:

Metadata information (relation's schema)

Name of relation

List of attributes and domains

Data information

Actual instances or rows of the relation

Optional comments may also be included (lines prefixed with %)

Here is an example of a small ARFF file:

% 1. Title: Hypothetical Database
% 
% 2. Sources:
%      (a) Creator: P. Bodily
%      (b) Institution: ISU
%      (c) Date: August, 2023

@RELATION hypo

@ATTRIBUTE length	CONTINUOUS
@ATTRIBUTE color	{Red, Green, Blue}
@ATTRIBUTE age		CONTINUOUS
@ATTRIBUTE neighbors	{1, 2-to-4, 5-to-9, more-than-10}
@ATTRIBUTE class     	{True, False}
  
@DATA
   5.1,Red,4,2-to-4,True
   4.9,Blue,4,1,True
   4.7,Red,3,more-than-10,False
   4.6,Green,5,2-to-4,True
   5.0,Blue,4,5-to-9,False
   5.4,Red,7,5-to-9,True

The relation's name is defined in the first non-comment line of the file:

@RELATION <relation-name>

Declaration is case-insensitive
<relation-name> is a space-free string

Attribute declarations take the form of an ordered sequence of @ATTRIBUTE statements, one per line:

@ATTRIBUTE <attribute-name> <domain>

Declaration is case-insensitive
<attribute-name> is a space-free string
<domain> is either
- CONTINUOUS (case-insensitive) for real/integer values
- A set of possible nominal values, enclosed in curly braces and delimited with commas
```
@ATTRIBUTE <attribute-name> {<nominal-value-1>, <nominal-value-2>, <nominal-value-3>, ...}
```
  - The nominal domain type is used for attributes whose values range over a (small) finite set
  - Nominal values are space-free, case-sensitive strings
Important: the order in which the attributes are declared indicates the column position in the data section of the file.

The data declaration is a single line denoting the start of the data segment in the file:

@DATA

Each instance is then coded on a single line, with a carriage return denoting the end of the instance. Attribute values for each instance are delimited by commas.