page_title: Object Process Methodology
section_title: Control links
hierarchical_section_title: Object Process Methodology / Syntax and semantics / Links / Control links
caption_attribution_description: English: OPM Condition State-Specified Transforming Link
context_page_description: Object Process Methodology is a conceptual modeling language and methodology for capturing knowledge and designing systems, specified as ISO/PAS 19450. Based on a minimal universal ontology of stateful objects and processes that transform them, OPM can be used to formally specify the function, structure, and behavior of artificial and natural systems in a large variety of domains.
  OPM was conceived and developed by Dov Dori. The ideas underlying OPM were published for the first time in 1995. Since then, OPM has evolved and developed.
  In 2002, the first book on OPM was published, and on December 15, 2015, after six years of work by ISO TC184/SC5, ISO adopted OPM as ISO/PAS 19450. A second book on OPM was published in 2016.
  Since 2019, OPM has become a foundation for a Professional Certificate program in Model-Based Systems Engineering - MBSE at EdX. Lectures are available as web videos on Youtube.
context_section_description: An event link and a condition link express an event and a condition, respectively. Control links occur either between an object and a process or between two processes.
  Event links
  An event link specifies a source event and a destination process to activate on event occurrence. Triggering a process initiates an attempt to execute the process, but it does not guarantee success of this attempt. The triggering event forces an evaluation of the process' precondition for satisfaction, which, if and only if satisfied, allows process execution to proceed and the process becomes active. Regardless of whether the precondition is satisfied or not, the event will be lost. If the precondition is not satisfied, process execution will not occur until another event activates the process and a successful precondition evaluation allows the process to execute.
  Basic transforming event links: A consumption event link is a link between an object and a process, which an instance of the object activates. Satisfaction of the process precondition and the subsequent process execution need to consume (affect) the instance of the activating object.
  Consumption event link: Graphically, an arrow with a closed arrowhead pointing from the object to the process with the small letter e (for event). The syntax of a consumption event link OPL sentence is: Object triggers Process, which consumes Object.
  Effect event link: Graphically, a bidirectional arrow with closed arrowheads at each end between the object and the process with a small letter e (for event). The syntax of an effect event link OPL sentence is: Object triggers Process, which affects Object.
  Basic enabling event links:
  Agent event link: An agent event link is an enabling link from an agent object to the process that it activates and enables. Graphically, a line with a filled circle ("black lollipop") at the terminal end extending from an agent object to the process it activates and enables with a small letter e (for event). The syntax of an agent event link OPL sentence is: Agent triggers and handles Process.
  Instrument event link: An instrument event link is an enabling link from an instrument object to the process that it activates and enables. Graphically, a line with an empty circle ("white lollipop') at the terminal end extending from the instrument object to the process it activates and enables with a small letter e (for event). The syntax of an instrument event link OPL sentence is: Instrument triggers Process, which requires Instrument.
  State-specified transforming event links:
  State-specified consumption event link: A state-specified consumption event link is a consumption link that originates from a specific state of an object and terminates at a process, which an instance of the object activates. Satisfaction of the process precondition, including the activating object instance being at its specified state, and the subsequent process execution consume the activating object instance. Graphically, an arrow with a closed arrowhead pointing from the object state to the process with the small letter e (for event). The syntax of a state-specified consumption event link OPL sentence is: Specified-state Object triggers Process, which consumes Object.
  Input-output-specified effect event link: An input-output-specified effect event link is an input-output-specified effect link with the additional meaning of activating the affecting process when the object enters the specified input state. Graphically, the input-output-specified effect link with a small letter e (for event). The syntax of an input-output specified effect event link OPL sentence is: Input-state Object triggers Process, which changes Object from input-state to output-state.
  Input-specified effect event link: An input-specified effect event link is an input-specified effect link with the additional meaning of activating the affecting process when the object enters the specified input state. Graphically, the input-specified effect link with a small letter e (for event. The syntax of an input-specified effect event link OPL senten
caption: OPM Condition state-specified transforming link
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