# BR-64 Item standard identifier must have a scheme identifier

The Item standard identifier (BT-157) shall have a Scheme identifier so the identifier’s registration scheme is unambiguous.

## Problem Description

> **ERROR**: EN 16931 core business rule (CEN)

## Context and Significance

This is an EN 16931 core rule. A standard item identifier (BT-157), most often a GTIN (formerly EAN), is only unambiguous together with its scheme. The error usually appears when an EAN barcode number is exported in cac:StandardItemIdentification without schemeID; for a GTIN use 0160. The value must belong to the ISO 6523 ICD list (BR-CL-21). Classification codes such as UNSPSC belong in BT-158 and are covered by BR-65.

## Solution

Set the schemeID attribute on cac:StandardItemIdentification/cbc:ID (CII: ram:SpecifiedTradeProduct/ram:GlobalID/@schemeID) to an ISO/IEC 6523 code, for example 0160 for a GTIN.

- [Validate XML](/en/xrechnung-validator?source=resource&rule=BR-64)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&rule=BR-64)

## Valid Examples

- BT-157 = 04012345678901 with schemeID="0160" (GTIN)

## Invalid Examples

- BT-157 standard item ID present but with no schemeID attribute

## Code Examples

### Valid XML
```
<cac:Item>
  <cac:StandardItemIdentification>
    <cbc:ID schemeID="0160">04012345678901</cbc:ID>
  </cac:StandardItemIdentification>
</cac:Item>
```

### Invalid XML
```
<cac:Item>
  <cac:StandardItemIdentification>
    <cbc:ID>04012345678901</cbc:ID>
  </cac:StandardItemIdentification>
</cac:Item>
```

## Affected Fields

- [BT-157 Item standard identifier](/resources/xrechnung/bt-157-item-standard-identifier)

## Related Rules

- [BR-65](/resources/kosit-validator-errors/br-65-item-classification-identifier-scheme-required)

## Validation Tools

- [Official KoSIT Validator](https://github.com/itplr-kosit/validator): Run the official KoSIT validator with the XRechnung configuration to check EN 16931 and XRechnung rules.
- [Convert PDF to XRechnung](/pdf-to-xrechnung): Find validation errors during conversion and review each correction.

## Related Resources

- [Official Specification](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)
- [All validation errors](/resources/kosit-validator-errors): Overview of the EN 16931, XRechnung and Peppol validation rules explained here.