'''Universal systemsSystems languageLanguage''' ('''USL''') is a systems [[modeling language]] and [[formal method]] for the specification and design of software and other complex systems. It was designed by [[Margaret Hamilton (scientist)|Margaret Hamilton]] based on her experiences writing flight software for the [[Apollo program]].<ref name="USL">[[Margaret Hamilton (scientist)|M. Hamilton]] and W. R. Hackler, "[http://www.htius.com/Articles/r12ham.pdf Universal Systems Language: Lessons Learned from Apollo]", IEEE Computer, Dec. 2008.</ref> The language is implemented through the 001 Tool Suite software by Hamilton Technologies, Inc.<ref>[http://www.htius.com 001 Tool Suite (1986-2020)]</ref> USL evolved from 001AXES which in turn evolved from AXES all of which are based on Hamilton's axioms of control. The 001 Tool Suite uses the preventive concept of Development Before the Fact (DBTF) for its life-cycle development process. DBTF eliminates errors as early as possible during the development process removing the need to look for errors after-the-fact.
==Philosophy==
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Primitive structures are universal in that they are able to be used to derive new abstract universal structures, functions or types. The process of deriving new objects (i.e., structures, types and functions) is equivalent to the process of deriving new types in a constructive type theory.
[[Image:ucs rules.png|center|frame|Figure. 1 The three primitive control structures and their rules form a universal foundation for constructing maps in the domains of time and space as FMaps and TMaps.]]
