In the A2A protocol, when a client sends a message to an agent, the agent might determine that fulfilling the request requires a stateful operation (e.g., “generate a report,” “book a flight,” “summarize a document”). This is where the Task Object comes into play. It is the fundamental, stateful unit of work processed by the A2A Server (remote agent) for an A2A Client, encapsulating the entire interaction related to achieving a specific goal or request.

Key characteristics of a Task include:

• Initiation and Identification: A Task is typically initiated based on a client’s request. The remote agent then creates and manages the Task, assigning it a unique, server-generated id (often a UUID). Many A2A interactions revolve around this Task and its id.
• Progresses through a defined lifecycle of states: submitted (Task has been received), working (Agent is actively processing the task), input-required (Agent needs more input to proceed), completed (Task finished successfully), failed (Task could not be completed due to an error), canceled (Task was terminated by the client or system)
• Interaction History: A Task is stateful and can involve multiple exchanges. It can contain a sequence of Messages (often in a historyfield), representing the conversational turns between the client and the agent within the context of that task.
• Outputs: A successfully completed Task typically produces one or more Artifacts — the immutable results or outputs of the agent’s work (e.g., a generated summary, a file, an image, or structured data).
• Orchestration and Context: While individual tasks are fundamental, A2A also supports more complex scenarios. For instance, the A2A Python SDK includes features like a “request context builder with referenceTasks“. This indicates capabilities within the A2A ecosystem to link and manage interdependent tasks, allowing for sophisticated orchestration where the context or outcome of one task can influence another. A Task object itself often includes a contextId to help group related tasks.

By defining interactions within the framework of Tasks, A2A provides a standardized way to manage both simple and complex collaborative efforts between AI agents.

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Task: The Unit of Collaboration

• Message: The Conversational Turns
  • Part: The Fundamental Content Units
• Artifact: The Result (immutable results)
  • Part: The Fundamental Content Units

참고: Understanding A2A — The Protocol for Agent Collaboration