# Cross-reference lookups

## Introduction

**Cross-reference lookups** are used for cases where sets of static values are commonly known by another value. For example:

**Weight measurements**

| Term     | Also known as... |
| -------- | ---------------- |
| Kilogram | Kg               |
| Gram     | g                |
| Cup      | c                |

**Months of the year**

| Term     | Also known as... |
| -------- | ---------------- |
| January  | Jan              |
| February | Feb              |
| March    | Mar              |

If you have source data which includes values that always need to be changed to an alternative term, a cross-reference lookup can be used to transform required data fields. 

For example, you might have an incoming payload which has a 'renewal month' field with values in the form 'January', 'February', 'March', etc. but also have a target connection which only accepts months in abbreviated form - 'Jan', 'Feb', 'Mar', etc.

In this scenario, you could add 12 `replace` [transformation functions](https://doc.wearepatchworks.com/product-documentation/process-flows/building-process-flows/process-flow-shapes/standard-shapes/map-shape/working-with-field-transformations/available-transform-functions) for any field that needs this conversion - but a more efficient approach is to add one `map` transformation function (associated with the appropriate **cross-reference lookup**) to required fields.

Patchworks provides a range of **cross-reference lookups** which you can [install](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/installing-cross-reference-lookups) and [use](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/using-a-cross-reference-lookup-in-field-transformations), or you can add your own.

## In this section

* [Accessing cross-reference lookups](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/accessing-cross-reference-lookups)
* [Installing cross-reference lookups](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/installing-cross-reference-lookups)
* [Adding a cross-reference lookup](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/adding-a-cross-reference-lookup)
* [Importing & exporting cross-reference lookups](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/importing-and-exporting-cross-reference-lookups)
* [Using a cross-reference lookup in field transformations](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/using-a-cross-reference-lookup-in-field-transformations)

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If required, cross-reference lookups can also be updated via the Patchworks API. For more information please see our [Cross-reference lookup API ](https://doc.wearepatchworks.com/product-documentation/developer-hub/patchworks-core-api/core-api-spotlights/working-with-cross-reference-lookup-api-requests)section.
{% endhint %}