# Adding data stores to services

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**Added in** `eventcatalog@2.59.0`

[Data stores](/docs/development/guides/data/introduction.md) in EventCatalog are a great way to document which data stores your services write to or read from.

What are data stores?

Data stores are containers that hold data in your architecture (e.g. databases, caches, object stores, search indexes, etc).

You can read more about data stores [here](/docs/development/guides/data/introduction.md).

## Specifying read/write relationships to data stores[​](#specifying-readwrite-relationships-to-data-stores "Direct link to Specifying read/write relationships to data stores")

To document the read/write relationships to data stores you need to specify the data stores in the **writesTo** or **readsFrom** array within your service frontmatter API.

In the example below the `OrderService` writes to the `OrdersDatabase` and reads from the `ProductRedisCache`.

/services/Orders/index.mdx (example)

```
---
id: OrderService
... # other service frontmatter
writesTo:
    # id of the data store this service writes to
    - id: OrdersDatabase
readsFrom:
    # id of the data store this service reads from
    - id: ProductRedisCache
      # optional version of the data store if none provided latest will be used
      version: 0.0.1
---
```

### Using semver versioning[​](#using-semver-versioning "Direct link to Using semver versioning")

**Added in** `eventcatalog@2.4.0`

You can use [semver](https://semver.org/) syntax when referencing your data stores in your services.

/domains/Orders/index.mdx (example)

```
---
id: PaymentDomain
... # other domain frontmatter
writesTo:
    # Latest minor version of OrdersDatabase will be added
    - id: OrdersDatabase
      version: 0.x.1
    # Minor and patches of this version will be linked
    - id: ProductRedisCache
      version: ^1.0.1
    # Latest version of this data store will be shown by default.
    - id: OrdersDatabase
---
<!-- Markdown contents... -->
```

You can choose not to provide a version for a data store. If no version is given **latest** is used by default.

### Visualizing data stores within a service[​](#visualizing-data-stores-within-a-service "Direct link to Visualizing data stores within a service")

When data stores get added within your services EventCatalog will visualize this for you either using the `NodeGraph` component or through the visualizer.

![Example](/assets/images/visualiser-with-data-16a711072efee53b2480d1a2153aa450.png)

You can see an example of this [here](https://demo.eventcatalog.dev/visualiser/services/OrdersService/0.0.3)