> For the complete documentation index, see [llms.txt](https://docs.rhinofcp.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rhinofcp.com/data-harmonization/creating-syntactic-mappings-from-custom-data-models.md).

# Creating Syntactic Mappings from Custom Data Models

You can create a syntactic mapping that uses a subset of already-mapped data. This is helpful if you want to do a data science project on a subset of data where you do not need the full OMOP mapping.

To complete this, you will first need to create a data schema, then create a new syntactic mapping.

### Prerequisites

Before you start, an existing data model should have already been created. You should know which fields you want to use in your data subset.

### Create a New Data Schema

{% stepper %}
{% step %}

### Select the project

Select the project that contains the syntactic mapping of the data.
{% endstep %}

{% step %}

### Open Data Schemas

Select **Data Schemas** from the menu on the left.

![](/files/20ebded78ad01daa7ff0dd1811d38b777d6a03c5)
{% endstep %}

{% step %}

### Create a new data schema

Select **Create New Data Schema** button in the upper right corner.

![](/files/2fedad12e309e29d9df1bb7986b3992c1570d4e8)
{% endstep %}

{% step %}

### Enter schema details

Enter the name and description of the data schema.
{% endstep %}

{% step %}

### Choose how to create the schema

Select the **Create Blank Data Schema** or **Upload From File** button. If you want to create your own schema from scratch, select create blank data schema. If you have a CSV file, select Upload from File and select the file from your computer or device.

![](/files/6fb04f99a092d216190c4d9c29dd8ce83324cc4a)
{% endstep %}

{% step %}

### Create the schema

Select the **Create New Data Schema** button. The schema appears. If you selected the **Create Blank Data Schema** button, a blank schema will appear like the following. If you chose **Upload From File** button, you’ll see the fields from your CSV file.

![](/files/75d910c918e54a1f3dfa346704f66f9fce55414c)
{% endstep %}

{% step %}

### Add fields

Next, add the name of the Schema Field, Identifier, Description, Role, Type, Type Params, Units, May Contain PHI, Permissions.
{% endstep %}

{% step %}

### Add additional fields

To add additional fields, select the **Add Fields** button.
{% endstep %}

{% step %}

### Save the schema

When complete, click **Save**.
{% endstep %}

{% step %}

### Create the syntactic mapping

Create a new Syntactic Mapping by following instructions in [Creating, Editing, and Removing a Syntactic Mapping](/data-harmonization/creating-editing-and-removing-a-syntactic-mapping.md). Make sure that the target data model is **Custom**. Select the new schema that you created in the previous steps for the Target field.

![](/files/3e67956810d5d572e2a6280717a9af43d5bd7386)
{% endstep %}
{% endstepper %}