The Mistral Workflow Language defines a specific structure for workflows. The top-level attributes for a workflow definition include type, input, and output. The type attribute specifies the workflow type (e.g., 'direct' or 'reverse'). The input attribute declares the parameters the workflow accepts, and output defines the data the workflow returns upon completion. The attribute workflow-meta is not a recognized or standard top-level attribute within the Mistral workflow definition specification. While metadata can be associated with various components, workflow-meta is not a defined keyword in the language.

A. Type: This is a mandatory attribute in a Mistral workflow definition that specifies the workflow type, such as direct or reverse.

C. Output: This is a standard, optional attribute used to define the data structure that the workflow will return after successful execution.

D. Input: This is a standard, optional attribute used to declare the input parameters that the workflow requires to start its execution.

1. OpenStack Documentation for Mistral: The official documentation for the Mistral Workflow Language v2 explicitly lists the valid top-level attributes for a workflow. The list includes version, type, input, output, vars, and tasks. The attribute workflow-meta is not mentioned.

Source: OpenStack. "Mistral Workflow Language v2 - Workflow Structure."

Reference: In the "Workflow Structure" section, the documentation details the main components of a workflow definition. It states: "A workflow definition is a mapping that has a name and a set of attributes: type, input, vars, output, tasks." This confirms that A, C, and D are valid attributes, while B is not. (Available on the official OpenStack documentation website).