How to create a JSON to be used in ItemFileReadStore?

I have to generate a JSON to be read by ItemFileReadStore. I need to create more than 15 columns, how do I represent that? I have read the documentation and it seems that it follows a certain structure: Dojo's official website

Currently I have it in the following way:

[identifier] => 00001
[label] => 10 /*eso es la cantidad de proveedores*/
[items] => Array
    (
        [0] => Array
            (
                [Proveedor1] => 100
            )

        [1] => Array
            (
                [Proveedor2] => 101
            )

But I think those will be rows and not columns, although I'm not sure, I have not managed to create a dojo table that is created from a json, so for the moment I'm assuming.

I need the table to be as follows:

Identifier, Label, Provider1, Provider2

0001, 2, 100, 101

0002, 2, 98, 86