code analyzer detected issues

[Khushboo2298]

code analyzer is detecting the below issues for fflib_SObjectUnitOfWork.cls
Apex classes should declare a sharing model if DML or SOQL/SOSL is used - lines 54, 96, 130

please guide me to resolve these issues

ApexSharingViolations (https://docs.pmd-code.org/pmd-doc-6.55.0/pmd_rules_apex_security.html#apexsharingviolations)