---
title: "What is an identifier?"
slug: "what-is-an-identifier"
tags: ["code"]
updated: 2025-07-14T13:39:51Z
published: 2025-07-14T13:39:51Z
canonical: "support.lusid.com/what-is-an-identifier"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://support.lusid.com/llms.txt
> Use this file to discover all available pages before exploring further.

# What is an identifier?

An *identifier* is a set of attributes that combine to identify a LUSID entity in some way. [See a list of identifiers for every entity](/v1/docs/what-is-an-entity).

Most entities have an identifier consisting of a [scope and a code](/v1/docs/what-is-a-scope). The code must be unique within the scope.

Some entities can have multiple, more complex identifiers, in which case the entity can be addressed by any, though note an identifier value may be shared between multiple entities:

- Instruments have unique and non-unique market identifiers (such as FIGI and ISIN) as well as a globally-unique, system-generated identifier. [More information](/v1/docs/understanding-instrument-identifiers).
- Certain other entities have user-defined property identifiers as well as a globally-unique, system-generated identifier. See below.

## Understanding user-defined property identifiers

The following types of entity do not have a scope and a code but rather at least one user-defined property identifier:

- `Person`, representing a [person of interest](/v1/docs/representing-people-in-lusid-using-person-entities) in your LUSID enviroment.
- `LegalEntity`, representing an [institution of interest](/v1/docs/representing-institutions-in-lusid-using-legal-entities).
- `InvestorRecord`, representing an [investor in a particular jurisdiction](/v1/docs/how-do-i-create-an-investor-record).
- `InvestmentAccount`, representing a link between an [investor and their investment account](/v1/docs/how-do-i-create-an-investment-account).
- A [custom entity](/v1/docs/extending-lusids-data-model-using-custom-entities) created to extend LUSID’s data model.

Note they can have more than one user-defined property identifier, perhaps reflecting different contexts in which they operate.

Under-the-hood, a user-defined property identifier has a [property type](/v1/docs/how-do-i-create-a-property-type) belonging to a particular domain. Consider the following example of an investor record:

```json
{
  "lusidInvestorRecordId": "LUID_00003EIC",
  "displayName": "John Doe",
  "description": "An investor record for John Doe",
  "identifiers": {
    "InvestorRecord/Identifiers/External": {
      "key": "InvestorRecord/Identifiers/External",
      "value": {
        "labelValue": "ABCDEFG"
      },
    },
    "InvestorRecord/Identifiers/Internal": {
      "key": "InvestorRecord/Identifiers/Internal",
      "value": {
        "labelValue": "1234567"
      },
    }
  },
  ...
}
```

This entity has:

- Two user-defined property identifiers, `InvestorRecord/Identifiers/External` and `InvestorRecord/Identifiers/Internal`. Each consists of:
  - A `domain` (the first part of the 3-stage property key), in this case `InvestorRecord`.
  - An `idTypeScope` (the second part of the 3-stage property key), in this case `Identifiers`. This happens to be the same value for these two identifiers, but need not be the case.
  - An `idTypeCode` (the third part of the 3-stage property key), in this case `External` and `Internal`. This value must be unique with the `idTypeScope`.
  - A `code` (the actual property value), in this case `ABCDEFG` and `1234567`.
- A globally-unique, system-generated `lusidInvestorRecordId` of `LUID_00003EIC` that is guaranteed to be unique and never change. This is identical in concept and structure to an instrument's [LUID](/v1/docs/what-is-a-lusid-instrument-id-or-luid).

Property types for user-defined property identifiers must exist before entities can be created. In this example, we would need to call the [CreatePropertyDefinition](https://www.lusid.com/docs/api/lusid/endpoints/property-definitions/CreatePropertyDefinition) API twice to create both `InvestorRecord/Identifiers/External` and `InvestorRecord/Identifiers/Internal` before creating the investor record they combine to identify.

For example, to create `InvestorRecord/Identifiers/External`:

```json
curl -X POST 'https://<your-domain>.lusid.com/api/api/propertydefinitions'
  -H 'Authorization: Bearer <your-API-access-token>'
  -H 'Content-Type: application/json-patch+json
  -d '{
    "constraintStyle": "Identifier",
    "domain": "InvestorRecord",
    "scope": "Identifiers",
    "code": "External",
    "displayName": "An external identifier for investor records",
    "lifeTime": "Perpetual",
    "dataTypeId": {"scope": "system", "code": "string"}
  }'
```

Note the following:

- The `constraintStyle` must be `Identifier` to distinguish this property type from standard property types.
- The `domain` must be the entity type to which the property type belongs: either `Person`, `LegalEntity`, `InvestorRecord`, ` InvestmentAccount` or the entity type name of a custom entity.
- The `scope` of the property type maps to the `idTypeScope` of identifiers.
- The `code` maps to the `idTypeCode`.
- The `lifeTime` must be `Perpetual`. Time-variant identifiers are not allowed.
- The `dataTypeId` must resolve to a string [data type](/v1/docs/what-is-a-data-type).