Flow Port and Flow Specification are deprecated in this version of SysML and are defined for backward compatibility. Source OMG Systems Modeling Language (SysML) 1.7beta1
TIP: Mathematica: COMING SOON! Webel's ultimate guide to using Abstract Data Types to create pseudo-classes WITH INHERITANCE in Wolfram Language, all modelled in SysML! [There's already some examples and some detailed policy notes.]