@article(Bruyn1988,
 author       = "W. Bruyn and R. Jensen and D. Keskar and P. Ward",
 year         = "1988",
 title        = "An Extended Systems Modeling Language Based on the Data Flow Diagram",
 journal      = "ACM SIGSOFT Software Engineering Notes",
 volume       = "13",
 number       = "1",
 pages        = "58--67",
 doi          = "10.1145/43857.43866",
)
@masterthesis(DeVries2013,
 author       = "B. DeVries",
 year         = "2013",
 title        = "Mapping of UML Diagrams to Extended Petri Nets for Formal Verification",
 school       = "Grand Valley State University",
 address      = "Allendale, Michigan",
 date = "April 2013",
 url          = "http://scholarworks.gvsu.edu/cistechlib/156",
)
@article(Harel1988,
 author       = "D. Harel",
 year         = "1988",
 title        = "On visual formalisms",
 journal      = "Communications of the ACM",
 volume       = "31",
 number       = "5",
 pages        = "514--530",
 doi          = "10.1145/42411.42414",
)
@unpublished(Harel1998,
 author       = "D. Harel",
 year         = "1998",
 title        = "Private conversation at OOPSLA Conference",
 address      = "Vancouver, British Columbia. Canada",
)
@misc(iLogix1990,
 author       = "i-Logix",
 year         = "1990",
 title        = "i-Logix technical presentation to Smiths Industries",
 address      = "Grand Rapids, Michigan",
)
@misc(iLogix1991,
 author       = "i-Logix",
 year         = "1991",
 title        = "i-Logix training cours",
 address      = "Andover, Massachusetts",
)
@book(Jorgensen2014,
 author       = "P. Jorgensen",
 year         = "2008",
 title        = "Software testing - a craftsman's approach",
 edition      = "4th",
 publisher    = "Taylor \& Francis",
 ISBN = "978-1-4665-6808-0",
 pages        = "I-XXIX, 1-464",
)