# DTP Sites: Services

Services are common logic implemented in a centralized location made accessible to the rest of the application to perform tasks in a common way. They live in [app/services](app/services), and are scripts that export a specific structure that identifies the service and provides a way to create, start, and stop them.

Services can't reference each other in their constructors, but they can reference each other in their `start` method with the caveat that the service you are referencing may not have had it's `start` method called, yet. DTP loads services in one loop, then starts them in a separate loop after they are loaded.

All other service methods implemented can reference all other services with the assumption that they are started and ready to provide full service.

```js
// myservice.js
// Copyright (C) 2021 Digital Telepresence, LLC
// License: Apache-2.0

'use strict';

const { SiteService } = require('../../lib/site-lib');

class MyService extends SiteService {

  constructor (dtp) {
    super(dtp, module.exports);
  }

  async start ( ) {
    /*
     * perform service initialization here
     */
  }

  /*
   * Implement service methods here
   */
}

module.exports = {
  logId: 'my-service',
  index: 'myService',
  className: 'MyService',
  create: (dtp) => { return new MyService(dtp); },
};
```