# Workflow basics - Ruby SDK

> This section explains Workflow basics with the Ruby SDK

## Develop a Workflow 

Workflows are the fundamental unit of a Temporal Application, and it all starts with the development of a [Workflow Definition](/workflow-definition).

In the Temporal Ruby SDK programming model, Workflows are defined as classes.

Have the Workflow class extend `Temporalio::Workflow::Definition` to define a Workflow.

The entrypoint is the `execute` method.

```ruby
class MyWorkflow < Temporalio::Workflow::Definition
  def execute(name)
    Temporalio::Workflow.execute_activity(
      MyActivity,
      { greeting: 'Hello', name: },
      start_to_close_timeout: 100
    )
  end
end
```

Temporal Workflows may have any number of custom parameters.
However, we strongly recommend that hashes or objects are used as parameters, so that the object's individual fields may be altered without breaking the signature of the Workflow.

### Customize Workflow Type 

Workflows have a Type that are referred to as the Workflow name.

The following examples demonstrate how to set a custom name for your Workflow Type.

You can customize the Workflow name with a custom name in a `workflow_name` class method call on the class.
The Workflow name defaults to the unqualified class name.

```ruby
class MyWorkflow < Temporalio::Workflow::Definition
  # Customize the name
  workflow_name :MyDifferentWorkflowName

  def execute(name)
    Temporalio::Workflow.execute_activity(
      MyActivity,
      { greeting: 'Hello', name: },
      start_to_close_timeout: 100
    )
  end
end
```

### Use Workflow constructors

Workflow constructors are useful if you have message handlers that need access to Workflow input: see [Initializing the Workflow first](/handling-messages#workflow-initializers). The `workflow_init` class method above `initialize` gives it access to [Workflow input](/handling-messages#workflow-initializers). When you use the `workflow_init` on your constructor, you give the constructor the same Workflow parameters as your `execute` method.

The SDK will then ensure that your constructor receives the Workflow input arguments that the [Client sent](/develop/ruby/client/temporal-client#start-workflow). The Workflow input arguments are also passed to your `execute` method. That always happens, whether or not you use the `workflow_init` class method above `initialize`.

Here's an example.
The constructor and `execute` must have the same parameters with the same types:

```ruby
class WorkflowInitWorkflow < Temporalio::Workflow::Definition
  workflow_init
  def initialize(input)
    @name_with_title = "Knight #{input['name']}"
  end

  def execute(input)
    Temporalio::Workflow.wait_condition { @title_has_been_checked }
    "Hello, #{@name_with_title}"
  end
end
```

## Workflow logic requirements 

Temporal Workflows [must be deterministic](https://docs.temporal.io/workflows#deterministic-constraints), which includes
Ruby Workflows. This means there are several things Workflows cannot do such as:

- Perform IO (network, disk, stdio, etc)
- Access/alter external mutable state
- Do any threading
- Do anything using the system clock (e.g. `Time.Now`)
- Make any random calls
- Make any not-guaranteed-deterministic calls

To prevent illegal Workflow calls, a call tracer is put on the Workflow thread that raises an exception if any illegal
calls are made.
Which calls are illegal is configurable in the Worker options.