# Model relationships and actors

Copy as Markdown[View as Markdown](/docs/development/guides/systems/model-relationships-and-actors.md)

***

**Added in** `eventcatalog@4.0`

Systems can describe how they relate to other systems and which people, roles, or external participants interact with them.

EventCatalog uses this information to render context diagrams for systems and domains.

![Product Catalog System context diagram](/assets/images/product-catalog-system-context-map-2a592cb9862dcd95ddf92e047b0b3812.png)

## Add relationships to other systems[​](#add-relationships-to-other-systems "Direct link to Add relationships to other systems")

Use `relationships` to connect one system to another system.

/domains/Shopping/systems/cart-system/index.mdx

```
---
id: cart-system
name: Cart System
version: 1.0.0
relationships:
  # id of the system it has a relationship with
  - id: promotion-system
    # version of the system (optional)
    version: 1.0.0
    # label used for edge in graph
    label: calculates discounts via
---
```

The `label` is shown on the relationship edge in context diagrams.

Relationships are one-directional. Define the relationship on the system that owns the source of the relationship.

## Add actors[​](#add-actors "Direct link to Add actors")

Use `actors` to show people, roles, or external participants that interact with a system.

/domains/Shopping/systems/cart-system/index.mdx

```
---
id: cart-system
name: Cart System
version: 1.0.0
# define any actors for that system
actors:
  # unique id for actor (shared across your catalog)
  - id: shopper
    name: Shopper
    # label used in the edge
    label: adds items and checks out
    # inbound or outbound
    direction: inbound
---
```

Use `direction: inbound` when the actor interacts with the system.

Use `direction: outbound` when the system reaches out to the actor, such as sending an email or notification.

## Show the context diagram[​](#show-the-context-diagram "Direct link to Show the context diagram")

Add `<ContextDiagram />` to a system page to show the system in context with related systems and actors.

/domains/Shopping/systems/cart-system/index.mdx

```
## Context Diagram

<ContextDiagram />
```

You can also open the context diagram directly:

```
/visualiser/systems/{system-id}/{version}/context
```

For the complete relationship and actor fields, see the [systems reference](/docs/development/guides/systems/reference.md).