# Workflow interface

Workflow encapsulates the orchestration of activities and child workflows. It can also answer synchronous queries and receive external events (also known as signals).

A workflow must define an interface class. All of its methods must have one of the following annotations:

  • @WorkflowMethod indicates an entry point to a workflow. It contains parameters such as timeouts and a task list. Required parameters (such as executionStartToCloseTimeoutSeconds) that are not specified through the annotation must be provided at runtime.
  • @SignalMethod indicates a method that reacts to external signals. It must have a void return type.
  • @QueryMethod indicates a method that reacts to synchronous query requests.

You can have more than one method with the same annotation (except @WorkflowMethod). For example:

public interface FileProcessingWorkflow {
    @WorkflowMethod(executionStartToCloseTimeoutSeconds = 10, taskList = "file-processing")
    String processFile(Arguments args);
    List<String> getHistory();
    String getStatus();
    void retryNow();
    void abandon();

We recommended that you use a single value type argument for workflow methods. In this way, adding new arguments as fields to the value type is a backwards-compatible change.