水平跟踪 纵向追踪

Vertical traceability identifies the origin of items (e.g., customer needs) and follows these same items as they travel through the hierarchy of the Work Breakdown Structure to the project teams and eventually to the customer. When the requirements are managed well, traceability can be established from the source requirement to its lower level requirements and from the lower level requirements back to their source. Such bidirectional traceability helps determine that all source requirements have been completely addressed and that all lower level requirements can be traced to a valid source.

水平跟踪”也是很重要的，在REQM的subpractice 3中提到 ，但它并不是需要满足双向可追溯性的必要条件。“水平跟踪”通过识别相关的工作组、产品组件的关系来避免潜在的冲突。这使项目可以在集成测试之前预计可能出现的问题（并且减轻或解决这些问题）。例如，同一个产品的两个相关部件，由两个工作组根据同一份需求分别负责。当一个组件对应的需求发生改变时，可能会影响到另一个组件。横跨两个组件的需求跟踪就能及时发现、规避或解决这些问题。因此，“水平跟踪”使项目可以在集成测试之前预计可能出现的问题（并且减轻或解决这些问题）。