Each 3rd-Party-Service is represented by a separate OSGI-Service-instance (type "GenericSubscribeService"). These services each contain a description (type "CrawlerDescription") of how to access "their" 3rd-Party-Service. Every time the OSGI-Bundle "com.openexchange.subscribe.crawler" is started these descriptions get updated via reading YML-files (one for each 3rd-Party-Service). So to update a "Crawler" a new YML-file has to be placed in the appropriate directory and the OSGI-Bundle has to be restarted.
When a user hits the refresh-button of a subscription the respective OSGI-Service creates a new workflow-instance (type "Workflow") from its description, inserts the user´s credentials (decrypted using his login password) and executes the workflow. The workflow then executes each each Step (type "Step") in order. The output of each step is given to its successor as input. The output of a workflow's final step is the wanted content (e.g. a list of Contacts) and is returned, via the OSGI-Service, to the OX-Server.