SysML1.0:

A property typed by a Block that does not have composite aggregation is classified as a reference property. 

MD SysML distinguishes between a SharedProperty and a true ReferenceProperty which both extend AbstractReferenceProperty.

SysML1.0:

SysML also supports properties with shared aggregation, as shown by a white diamond symbol on an association. Like UML, SysML defines no specific semantics or constraints for properties with shared aggregation, but particular models or tools may interpret them in specific ways.

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