# BT-158 Item Standard Identifier Scheme

The scheme identifier for the item standard identifier.

## Quick answer

The scheme identifier for the item standard identifier.

> **Line items**: The goods or services on each invoice line, including quantities, prices, and VAT.

- validate
- convert

## In plain language

The scheme identifier for the item standard identifier.

The scheme identifier for the item standard identifier.

Identifies the invoiced goods or services for buyer, seller, and automated procurement or inventory matching.

## What you usually enter here

Identifier scheme code

Typical valid values include: 0160

Defined by EN 16931 for invoice line item identification; mandatory item names and optional identifiers must follow the listed scheme and country code rules.

## What goes wrong often

Avoid values like: GTIN

Relevant rule codes: BR-CL-21

## Examples in context

Identifies the invoiced goods or services for buyer, seller, and automated procurement or inventory matching.

Defined by EN 16931 for invoice line item identification; mandatory item names and optional identifiers must follow the listed scheme and country code rules.

## Valid Examples

- 0160

## Invalid Examples

- GTIN

## Related Fields

Identifies the invoiced goods or services for buyer, seller, and automated procurement or inventory matching.

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

## XML mapping and field facts

Open the technical reference if you need XML paths, validator rule codes, legal wording, or schema-specific mapping details.

### Field ID:
BT-158

### Data Type:
identifier

### Cardinality:
0..1

### Requirement:
Optional

### Since Version:
Optional

## XML Implementation

### UBL 2.1 Syntax
```
/Invoice/cac:InvoiceLine/cac:Item/cac:StandardItemIdentification/cbc:ID/@schemeID
```

## Validation Rules

### BR-CL-21
BR-CL-21

## Why the standard cares about this field

### Business Context
Identifies the invoiced goods or services for buyer, seller, and automated procurement or inventory matching.

### Legal Requirement
Defined by EN 16931 for invoice line item identification; mandatory item names and optional identifiers must follow the listed scheme and country code rules.

## Official sources and tools

- [KoSIT Validator](https://erechnungsvalidator.service-bw.de/)
- [Invoice Converter](/pdf-to-xrechnung)
- [XRechnung Standard](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)