Tracing Requirements 1

The Role of Traceability in Systems Development  Experience has shown that the ability to trace requirements artifacts through the stages of specification, architecture, design, implementation, and testing is a significant factor in assuring a quality product.  Software developed in many areas for certain customers may have mandated traceability requirements (e.g. the FDA). 2

Definition of Traceability  According to IEEE [1994] traceability is: “The degree to which a relationship can be established between two or more products of the development process, especially products having a predecessor-successor or master-subordinate relationship to one another; for example the degree to which the requirements and design of a given software component match.” “The degree to which each element in a software development product establishes its reason for existing; for example, the degree to which each element in a bubble chart references the requirement it satisfies.” 3

The Traceability Relationship  A traceability relationship is a dependency relationship between two project elements. A B traces Element B is in some way Dependent on element A 4

The Traceability Relationship (Cont’d)  A dependency relationship states that a change in one element (e.g., a use case) may affect another element (e.g., a test case), but the reverse is not necessarily true.  Additional meanings associated with the traces (or traced by) relationship can be inferred from the context. E.g., in the previous example, the relationship infers that the use case is “tested by” the test case. 5

A Generalized Traceability Model Stakeholder Need Product Feature Supplementary Requirements Use Case Test Cases Use-Case Realization Implementation System Definition System Test traces 6

Tracing Requirements in the System Definition Domain  This is called requirement-to- requirement traceability.  It includes: Tracing user needs to features Tracing features to use cases Tracing features to supplementary requirements 7

Tracing User Needs to Features Traceability Matrix: User Needs versus Features Feature 1Feature 2...Feature n Need 1 X Need 2 XX … XX Need m X 8

Examining the Traceability Matrix for Possible Errors  If inspection of a row fails to detect any Xs, a possibility exists that no feature is yet defined to respond to a user need. This might be acceptable, but it raises a red flag.  If inspection of a column fails to detect any Xs, possibility exists that a feature has been included for which there is no defined product need.  The traceability matrix can be helpful when changes in user needs occur. 9

Tracing Features to Use Cases  It is important to ensure that the features can be related to the use cases proposed for the system.  A matrix similar to the Needs versus Features matrix can be used. 10

Tracing User Needs to Features Traceability Matrix: Features versus Use Cases Use Case 1Use Case 2...Use Case k Feature 1 XX Feature 2 XX … X Feature n XX 11

Examining the Traceability Matrix for Errors  If inspection of a row fails to detect any Xs, a possibility exists that no use case is yet defined to respond to a feature. This is a red flag.  If inspection of a column fails to detect any Xs, a possibility exists that a use case has been included for which there is no known feature that requires it. That is, this use case may not be required. 12

Tracing Features to Supplementary Requirements Traceability Matrix: Features versus Supplementary Requirements Supplementary Requirement 1 Supplementary Requirement 2...Supplementary Requirement p Feature or Sys Req 1 XX Feature or Sys Req 2 XX … XX Feature or Sys Req j X 13

Tracing Requirements to Implementation  First we trace use cases to use case realizations as we did before.  We then follow the traceability relationship to the component parts of the use case realization, the classes (code).  We must do something similar for supplementary requirements. In this case we trace the requirements to a collaboration (which we need to name since it doesn’t come from a use case). See next slide. 14

Tracing Supplementary Requirements to Implementation Sync Clock > Requirements - The clocks shall... - Every 24 hours... - Synchronization occurs... Design Model Collaboration Participating classes 15

Tracing from Requirements to Testing  A comprehensive approach to testing is to assure that every use case is tested by one or more test cases.  In fact, each possible scenario for a use case needs to be tested by one or more test cases.  We can create a traceability matrix that maps use cases to test cases.  Requirements that are not expressed as use cases are either traced individually to scenarios and test cases or grouped into “requirements packages” that operate in the same logical fashion as use cases. 16

Traceability Matrix for Use Cases to Test Cases Use CaseScenario NumberTest Case ID Control Light Run Vacation Profile

Mechanisms for Managing Traceability Matrices  For a large project creating and managing the traceability matrices can be an overwhelming task due to the problems of correctly updating the information when changes (e.g., to requirements) occur. Mechanisms to help include: Spreadsheets Relational Data Bases Specialized Traceability Management Tools 18