Investigate using BPML

Angel, one of the panelists at the hackathon, suggested we look into using [business process markup language](https://en.wikipedia.org/wiki/Business_Process_Modeling_Language) for workflow definitions, as it's rather well-established, and has tools out there that would likely be compatible ([example tool](http://demo.bpmn.io/))

首先阅读链接的 Business Process Modeling Language 概览，并检查示例 BPMN 工具，以了解所提议的格式和兼容性目标。定义将 BPML 用于工作流定义的范围，并确定完整集成需要证明什么；issue 未列出任何文件或测试。

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