# Step 4: Validate Data

> **Prerequisite:** You should have multiple tags flowing from [Step 3](https://docs.umh.app/getting-started/2-organize-data). If not, complete that first!

## The Problem

Right now, ALL your data goes into `_raw` - no validation:

* DB1.DW20 could suddenly send "hello" instead of a number
* Critical vibration data might arrive with wrong units
* Typos in tag names create duplicate data streams

**How do you ensure data quality?** Data Models!

## Part 1: Create Your First Data Model

Let's create a model for a CNC machine's vibration data.

### Add a Data Model

1. Go to **Data Models** → **Add Data Model**
2. **Instance:** Select your instance
3. **Name:** `cnc`
4. **Description:** "CNC machine vibration monitoring"

### Define the Structure

In the **Data Model Structure** section, add this YAML:

```yaml
vibration:
  x-axis:
    _payloadshape: timeseries-number
  y-axis:
    _payloadshape: timeseries-number
```

**What this means:**

* Your CNC model has a `vibration` folder
* Inside are two measurements: `x-axis` and `y-axis`
* Both must be numbers (enforced automatically!)

![Data Model Creation](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-7349a5d89c78da881ff9843e51f0005f567d0e1a%2F3-models-cnc.png?alt=media)

Click **Save & Deploy**.

![Data Model List](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-6d1cf79f97951658a6c2cf10f092cefb1cd9d7d5%2F3-models.png?alt=media)

💡 **Behind the scenes:** The system automatically creates a data contract called `_cnc_v1`. This contract will enforce your model's structure. [Learn more about data contracts →](https://docs.umh.app/usage/data-modeling/data-contracts)

## Part 2: Use Your Model in a Bridge

### Find Your Contract Name

1. Go to **Contracts** tab
2. Find `_cnc_v1` - this was auto-generated from your model
3. Note the structure it expects

![Contract View](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-3688ea02b4be8c023fb9a8868ad10a49051ffc92%2F3-contracts.png?alt=media)

### Update Your Bridge

Go back to your S7 bridge from Step 3. In the **Always** section, change:

```javascript
// OLD: Everything goes to _raw
msg.meta.data_contract = "_raw";
```

To:

```javascript
// NEW: Everything goes to our validated model
msg.meta.data_contract = "_cnc_v1";
```

![Incorrect Processing Setup](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-a8d57ab08169c3c903945b697fe979e23b359785%2F3-bridge-cnc-wrong.png?alt=media)

Click **Save & Deploy**.

## Part 3: Experience Validation (It Will Fail!)

![Deployment Failed](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-a3b030d7252081b8315ab7afa08c3d3f91308f3e%2F3-bridge-cnc-deploy-failed.png?alt=media)

**Your deployment fails!** Look at the error:

```
schema validation failed for message with topic 'umh.v1.enterprise.sksk._cnc_v1.DB1.DW20':
Valid virtual_paths are: [vibration.x-axis, vibration.y-axis].
Your virtual_path is: DB1.DW20
Fix: Update the bridge to set meta.virtual_path to 'vibration' and meta.tag_name to 'x-axis' or 'y-axis'
```

Data models ENFORCE structure. Your S7 address `DB1.DW20` doesn't match the expected paths `vibration.x-axis` or `vibration.y-axis`.

**Two new concepts here:**

1. Deployments can fail not only if the connection is bad (learned in Step 2)
2. But also if the bridge throws validation errors

## Part 4: Fix with Smart Routing

Instead of forcing ALL data into the model, let's be selective. Change your **Always** section back:

```javascript
// Most data stays unvalidated
msg.meta.data_contract = "_raw";
msg.meta.tag_name = msg.meta.s7_address;
return msg;
```

Now update your condition for DB1.DW20:

```javascript
// Special handling for DB1.DW20: Route to validated model
msg.payload = parseFloat(msg.payload) * 1.0;
msg.meta.data_contract = "_cnc_v1";  // Use validated model
msg.meta.virtual_path = "vibration";  // Required: matches model structure
msg.meta.tag_name = "x-axis";         // Required: matches model field
msg.meta.unit = "raw";
return msg;
```

![Correct Processing Setup](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-988305672c172545df1432e2f4aecc70f4d266ba%2F3-bridge-cnc-processing-correct.png?alt=media)

**What this does:**

* DB1.DW20 → Validated as `vibration.x-axis` in CNC model
* All other tags → Continue to `_raw` (no validation)

Click **Save & Deploy**. Now it succeeds!

## Part 5: Success! View Your Validated Data

![Topic Browser with Validated Data](https://3966587046-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FPQ7UY9eT1SiICDqYFZdA%2Fuploads%2Fgit-blob-d70610e56f1c9c5d72d516a21cc3d2dc0df4e81a%2F3-topic-browser-correct.png?alt=media)

In **Topic Browser**, you now see:

```
enterprise.sksk._cnc_v1.vibration.x-axis    [12345]  ✓ Validated
enterprise.sksk._raw.DB1.S30.10             ["text"]  (Unvalidated)
enterprise.sksk._raw.DB3.I270               [789]     (Unvalidated)
```

**How validation works:**

* The CNC model guarantees `x-axis` is always a number
* If someone sends text, it's rejected at the bridge
* Other data flows normally through `_raw`

## Concepts Learned

Building on previous guides, you now understand:

* **Data Models** - Reusable templates defining data structure
* **Payload Shapes** - Type validation (timeseries-number, etc.)
* **Schema Validation** - Automatic enforcement at the bridge
* **Auto-generated Contracts** - Models create contracts like `_cnc_v1`
* **Validation Errors** - Deployments fail if data doesn't match
* **Selective Validation** - Route specific data to validated models

## What's Next?

You now have a complete data pipeline with:

* ✅ Automatic tag discovery (Step 3)
* ✅ Smart organization (Step 3)
* ✅ Data validation (Step 4)

**Ready for production?** Check out:

* [Production Guide](https://docs.umh.app/production) - Sizing, security, monitoring
* [Data Modeling Deep Dive](https://docs.umh.app/usage/data-modeling) - Advanced models
* [Stream Processors](https://docs.umh.app/usage/data-modeling/stream-processors) - One way to transform device data to business KPIs

***

**Congratulations!** You've mastered the fundamentals of UMH Core. Your data is now organized, validated, and production-ready. 🎉