OCL is important to the understanding of both the UML and SysML specifications because it is used to define the semantics and constraints of the modeling elements and relationships in both languages. OCL is part of the UML standard and is adopted by SysML as a complementary language. OCL can also be used to specify queries, expressions and operations on models. OCL is not directly related to a typical high-level domain model, tool-generated XMI for a SysML model, or software developers’ modifications to a SysML model. References: OMG-Certified Systems Modeling Professional - Model Builder – Advanced (OCUP2-ADV) Examination Guide Version 1.0, Section 4.3