David Lorge Parnas

Originator of the concept of information hiding in modular programming, Parnas is a Canadian early pioneer of software engineering whose work became a foundational element of object-oriented programming. He has also been noted for his advocacy of precise documentation.

Parnas was born in 1941 in the United States and acquired Canadian citizenship later in life. He completed his undergraduate and graduate studies at Carnegie Mellon University, receiving his Ph.D. in 1965. He held academic positions at a number of institutions over the course of his career, including Carnegie Mellon University, the University of North Carolina, the University of Maryland, the Technische Hochschule Darmstadt, the University of Victoria, McMaster University, and University College Dublin.

He made his most influential contribution in a landmark 1972 paper titled "On the Criteria to Be Used in Decomposing Systems into Modules," in which Parnas introduced the principle of information hiding. This principle held that each module of a software system should conceal its internal design decisions from other modules, exposing only what was strictly necessary through a well-defined interface. The concept became a foundational element of software engineering and later a cornerstone of object-oriented programming.

Parnas also became widely known for his ethical stance on the Strategic Defense Initiative. In 1985 he resigned from an advisory panel for the project, arguing that the software required for a reliable missile defense system could not be built with the engineering methods then available. His resignation attracted considerable public attention and sparked debate within the computing community about the responsibilities of software engineers.

Throughout his career, he has championed the use of precise, mathematically grounded documentation as an essential discipline in software development. He received numerous honors for his contributions, including the ACM SIGSOFT Outstanding Research Award.