# How Feeds are Resolved

## Task Runner

All Switchboard Oracle Jobs are executed by the task-runner, an engine used by oracles to fetch data in a secure and efficient manner. Understanding how Oracle jobs are processed is essential before creating them. Oracle Jobs must define an array of tasks executed sequentially. Any task producing a value (String, JSON, or Decimal) will be assigned to the job's context for that particular run.

The Task Runner Context can be interpreted as:

```typescript
// Context 
{
    current_value: string | JSON | Decimal,
    variable_cache: Map<string, string | JSON | Decimal>,
}
```

## Schemas

Switchboard feeds are composed of Oracle Jobs, a schema designed for efficient and safe fetching of arbitrary numeric data from various sources. Oracle nodes run feeds by aggregating the results of jobs within a feed definition and computing a median.

#### **Feeds Schema**

```
{
    jobs: [
        // Oracle Job 1
        {
            tasks: [ ... ]
        },
        // Oracle Job 2
        {
            tasks: [ ... ]
        }
    ]
}
```

Oracle Jobs are composed of tasks. Tasks are like instructions to fetch data or compute certain outputs. There are several [Task Types](https://docs.switchboard.xyz/custom-feeds/task-types) available, and they can be strung together to create some complex logic.

#### Oracle Jobs Schema

```
{
    tasks: [
        // task 1
        {
            ...
        },
        // task 2
        {
            ...
        }
    ]
}
```

## Variable Expansion

Using [Variable Overrides](https://docs.switchboard.xyz/custom-feeds/advanced-feed-configuration/data-feed-variable-overrides) and the [CacheTask](https://docs.switchboard.xyz/custom-feeds/advanced-feed-configuration/variables-with-cachetask), users can assign variables in a job and use them within the same job in a downstream task.

So in a downstream task, you can invoke the variable with the syntax: `${VARIABLE_NAME}.`

Here's an HttpTask where the URL is pulled from a variable:

```
[
    // ... Cache Task or Secrets Task (or both) must come first ...
    {
        httpTask: {
            url: "${MY_CONFIGURED_HTTP_URL}"
        }
    },
    {
        jsonParseTask: {
            path: "$.price"
        }
    }
]
```

Internally, the variables are being string-replaced within the executed job definitions. This can be a good tool for deduplicating logic in complex jobs.

## Resolution

In order for a task runner result to be valid, its current\_value must be some numeric value. Intermediate calls may produce non-numeric values (like HttpTasks, JsonParseTasks, etc), but the final value will be the result of the job.