# Classification fields

### What are classification fields?

Classification field predictions *categorise* content on a document into a predefined set of classifications. These are distinct from e.g. *extraction* type fields which make predictions about the content of a document.

### Classification types

#### Multi-class

A **multi-class** field is a type of document *classification* that assigns a single category, or *class* to a document. For example, the `invoice.currencyCode` field determines the currency used in an invoice. It is implemented as a **multi-class** field as there is usually only a single currency used in a single invoice.

#### Multi-label

A **multi-label** field is a similar type of classification, but instead of assigning a single category to a document, a **multi-label** classification can assign *many* categories, or *labels* to a document. For example, the `document.type` field determines which of Sypht's fieldsets are applicable to a given document. Since multiple fieldsets can be applicable to a single document, this field is implemented as a **multi-label** field.

### Samples

For **multi-class** and **multi-label** fields, the value returned for each field is a JSON object.

Here is an example of output for the `invoice.currencyCode` **multi-class** field:

{% code title="Multi-class example" %}

```javascript
{ 
  "name": "invoice.currencyCode",
  "value": {
    "invoice.currencyCode.AUD": {"value": true, "confidence": 0.69}, 
    "invoice.currencyCode.EUR": {"value": false, "confidence": 0}, 
    "invoice.currencyCode.GBP": {"value": false, "confidence": 0}, 
    "invoice.currencyCode.MYR": {"value": false, "confidence": 0}, 
    "invoice.currencyCode.NZD": {"value": false, "confidence": 0.29}, 
    "invoice.currencyCode.SGD": {"value": false, "confidence": 0}, 
    "invoice.currencyCode.Unknown": {"value": false, "confidence": 0.02}
  },
  "confidence": 0.69,
  "boundingBox": null
}
```

{% endcode %}

The list of keys in the object enumerate each possible class/label for the field. For the `invoice.currencyCode` shown above, there are seven possible classes, six of which represent a currency code and a seventh `Unknown` class for cases where Sypht cannot determine the currency. Note that each class is qualified with the field name.

### Decoding classifications

Each class/label has a value and a confidence. For multi-class fields (as above), only a single class will have a value of `true`.

For multi-label fields (such as `document.type`), multiple labels can have a value of `true`. Here is an example of output for the `document.type` multi-label field that demonstrates how multiple labels can simultaneously have a value of true:

{% code title="Multi-label example" %}

```javascript
{
  "name": "document.type",
  "value": {
    "bank": { "value": false, "confidence": 1 },
    "bill": { "value": false, "confidence": 1 },
    "bpay": { "value": false, "confidence": 1 },
    "electricity": { "value": false, "confidence": 1 },
    "generic": { "value": false, "confidence": 1 },
    "invoice": { "value": true, "confidence": 0.96 },
    "issuer": { "value": true, "confidence": 0.94 },
    "ndis": { "value": false, "confidence": 0.93 },
    "paystub": { "value": false, "confidence": 1 },
    "recipient": { "value": true, "confidence": 0.81 },
    "statement": { "value": false, "confidence": 1 },
    "toll": { "value": false, "confidence": 0.99 },
    "vehicle": { "value": true, "confidence": 0.76 }
  },
  "confidence": 0.511464907008,
  "boundingBox": null
}
```

{% endcode %}

Note that `invoice`, `issuer`, `recipient` and `vehicle` all have values of `true`.


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