Bi-directional Traceability

Traceabilities are of two kinds:

1. Vertical Traceability
2. Horizontal Traceability

Bidirectional traceability is tracing requirements both forward and backwards (in Horizontal) AND Top to Bottom, & Bottom to Top (in Vertical) through all the phases of software development lifecycle.

Vertical traceability is tracing customer requirements from requirements phase thru System Test / UAT phase and from System Test / UAT phase back to customer requirements phase. These traceabilities can be established if the requirements are well managed. Vertical traceability helps determine that all the source requirements have been completely addressed and that all lower level requirements and selected work products can be traced to a valid source.

Forward traceability ensures all requirements have been captured, while backward traceability ensures no additional functionality (gold plating) has not been introduced into the system.

If a requirement is added or withdrawn, the development team must be aware of the design elements / development modules / test cases, etc. where the impact would be felt and changes need to be carried out.

How does bidirectional traceability help?

1. To measure the impact of requirement changes. One requirement may spawn multiple design elements. In this case, each such design element should be traceable backwards to the same requirement.
2. To know that all requirements have been implemented in the system. (Forward traceability ensures this).
3. To ensure that no unwanted functionality has been incorporated into the system. (Backward traceability ensures this).

Vertical Traceability: Within a work product (BRS, SRS, HDL, LDL, Test Plan, etc.), the inter-relationships between various requirements is called vertical traceability. Each requirement is related to other requirement/s by virtue of functionality. Vertical Traceability ensures that all requirements have been captured, gaps in functionality have been identified, and that there is no duplication of requirements.