Goal structuring notation: Difference between revisions

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'''Goal structuring notation''' (GSN) is a graphical argument used to document and present proof that [[Safety engineering|safety]] goals have been achieved, in a clearer format than plain text.<ref name="GeRijoPaige2012">{{cite journal | last1 = Ge | first1 = Xiaocheng | last2 = Rijo | first2 = Rui | last3 = Paige | first3 = Richard F. | last4 = Kelly | first4 = Tim P. | last5 = McDermid | first5 = John A. | title = Introducing Goal Structuring Notation to Explain Decisions in Clinical Practice | journal = Procedia Technology | date = 2012 | volume = 5 | pages = 686–695 | issn = 2212-0173 | doi = 10.1016/j.protcy.2012.09.076 | pmid = | url = }}</ref> The notation is a diagram that builds its [[safety case]] through logic-based maps.<ref name="RichBlanchardMcCloskey2007">{{citation | last1 = Rich | first1 = K.J.N. | last2 = Blanchard | first2 = H. | last3 = McCloskey | first3 = J. | title = 2nd IET International Conference on System Safety 2007 | chapter = The use of goal structuring notation as a method for ensuring that human factors is represented in a safety case | date = 2007 | volume = 2007 | pages = 217–222 | publisher = IEE | doi = 10.1049/cp:20070467 | isbn = 978-0-86341-863-1 | chapter-url = }}</ref> Originally developed at the University of York during the 1990s, it gained popularity in 2012 and has been used to track safety assurances in industries such as traffic management and nuclear power.<ref name="Spriggs2012">{{cite book |last=Spriggs |first=John |title=GSN - The Goal Structuring Notation |date=2012 |publisher=Springer London |doi=10.1007/978-1-4471-2312-5 |isbn=978-1-4471-2311-8 |url=https://link.springer.com/book/10.1007/978-1-4471-2312-5}}</ref> By 2014, it had become the standard{{cn|date=February 2022}} format for graphic documentation of safety cases and was being used in other contexts such as [[patent claim]]s, [[ Debate team|debate strategy]], and legal arguments.<ref>{{cite web |last=Cabot |first=Jordi |date=12 February 2014 |url=https://modeling-languages.com/goal-structuring-notation-introduction/ |title=Goal Structuring Notation – a short introduction |website=Modeling Languages |access-date=21 June 2018}}</ref>

== Criticism ==

[[Charles Haddon-Cave]] in his review of the [[2006 Royal Air Force Nimrod crash|Nimrod accident]] commented that the top goal of a GSN argument can drive a conclusion that is already assumed, such as that a platform is deemed acceptably safe. This could lead to the safety case becoming a "self-fulfilling prophesy", giving a "warm sense of over-confidence" rather than highlighting uncertainties, gaps in knowledge or areas where the mitigation argument was not straightforward.<ref name=nimrod-review>{{citecitation |last=Haddon-Cave QC |first=Charles |author-link=Charles Haddon-Cave |title=The Nimrod Review |title-link=2006 Royal Air Force Nimrod crash#Nimrod Review |date=28 October 2009 |publisher=The Stationary Office |publication-place=London }}</ref> This had already been recognised by Habli and Kelly, who warned that a GSN diagram was just a depiction, not the safety case itself, and likened it to Magritte's painting [[The Treachery of Images]].<ref name=gsn-depictions>{{cite conference |last1=Habli |first1=Ibrahim |last2=Kelly |first2=Tim |title=Safety Case Depictions vs. Safety Cases – Would the Real Safety Case Please Stand Up? |conference=23rd International System Safety Conference |date=August 2007 |url=https://www-users.cs.york.ac.uk/~tpk/iet2007.pdf }}</ref> Haddon-Cave also criticised the practice of consultants to produce "outsize GSN charts" that could be yards long and became an end in themselves rather than an aid to structured thinking.

== History ==

The goal structuring notation was first developed at the [[University of York]] during the ASAM-II (A Safety Argument Manager II) project in the early 1990s, to overcome perceived issues in expressing safety arguments using the [[Toulmin method]]. The notation was further developed and expanded by Tim Kelly, whose PhD thesis contributed systematic methods for constructing and maintaining GSN diagrams, and the concept of ′safety case patterns′ to promote re-use of argument fragments.<ref name=Kelly1998>{{cite thesis |last=Kelly |first=Timothy Patrick |date=September 1998 |degree=PhD |publisher=University of York |url=https://www-users.cs.york.ac.uk/tpk/tpkthesis.pdf |title=Arguing Safety – A Systematic Approach to Managing Safety Cases}}</ref> During the late 1990s and early 2000s, the GSN methodology was taught on the Safety Critical Systems Engineering course at York, and various extensions to the GSN methodology were proposed by Kelly and other members of the university's High Integrity Systems Engineering group.<ref>{{cite journal |last1=Hawkins |first1=R.D. |last2=Kelly |first2=T.P. |title=A Systematic Approach for Developing Software Safety Arguments |date=July 2010 |journal=Journal of System Safety |volume=46 |issue=4 |pages=25-3325–33 |issn=0743-8826}}</ref>

By 2007, goal structuring notation was sufficiently popular that a group of industry and academic users came together to standardise the notation and its surrounding methodology, resulting in publication of the GSN Community Standard in 2011. From 2014, maintenance of the GSN standard moved under the auspices of the [[Safety-Critical Systems Club|SCSC's]] Assurance Case Working Group.<ref name=gsn2>{{cite book |author=The Assurance Case Working Group |date=Jan 2018 |url=https://scsc.uk/r141B:1 |title=Goal Structuring Notation Community Standard Version 2}}</ref> As at 2022, the standard has reached Version 3.<ref>{{cite book |author=The Assurance Case Working Group |date=May 2021 |url=https://scsc.uk/r141C:1 |title=Goal Structuring Notation Community Standard Version 3 |isbn=979-8451294949}}</ref>