A viewpoint is a specification of the conventions and rules for constructing and using a view for the purpose of addressing a set of stakeholder concerns (OMG 2010)
OMG. 2010. OMG Systems Modeling Language (OMG SysML™), Version 1.3. Needham, MA, USA: Object Management Group. Available at http://www.omg.org/technology/documents/domain_spec_catalog.htm#OMGSysML - derived from IEEE 1471.