Business Rules Engine separates reusable lookup logic from procedural rule execution. Decision Matrices contain business-rule lookup tables with defined input and output columns. When supplied with input values, the matrix searches for the applicable row and returns its configured output. Salesforce describes Decision Matrices as useful for implementing complex rules in a systematic and readable manner.

Expression Sets orchestrate more sophisticated decision logic. They can execute calculations, conditional branches, aggregations, constants, variables, and matrix lookups. An Expression Set can therefore call a Decision Matrix at the appropriate point in a licensing or eligibility process and use the returned value in subsequent calculations or decisions. Salesforce specifically documents Expression Sets calling Decision Matrices and consuming the output corresponding to the matching matrix row. This architecture allows policy data and procedural calculations to be maintained independently. For example, a licensing fee table can be maintained in a Decision Matrix while an Expression Set calculates intermediate values, invokes the matrix, and produces the final fee. The other options reverse these functions or mischaracterize the data interface. Decision Matrices do not perform the broader sequence of calculations attributed to Expression Sets.

Study Guide References: Business Rules Engine; Expression Sets; Decision Matrices; Licensing Business Rules; Declarative Decision Automation.