Fundamentals of Systems Engineering Prof. Olivier L. de Weck, Mark Chodas, Narek Shougarian Session 3 System Modeling Languages 1 Reminder: A1 is due today ! 2 3 Overview Why Systems Modeling Languages? Ontology, Semantics and Syntax OPM – Object Process Methodology SySML – Systems Modeling Language Modelica What does it mean for Systems Engineering of today and tomorrow (MBSE)? 4 Exercise: Describe the “Mr. Sticky” System Work with a partner (5 min) Use your webex notepad/white board I will call on you randomly We will compare across student teams © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 5 Why Systems Modeling Languages? Means for describing artifacts are traditionally as follows: Natural Language (English, French etc….) Graphical (Sketches and Drawings) These then typically get aggregated in “documents” Examples: Requirements Document, Drawing Package Technical Data Package (TDP) should contain all info needed to build and operate system Advantages of allowing an arbitrary description: Familiarity to creator of description Not-confining, promotes creativity Disadvantages of allowing an arbitrary description: Room for ambiguous interpretations and errors Difficult to update if there are changes Handoffs between SE lifecycle phases are discontinuous Uneven level of abstraction Large volume of information that exceeds human cognitive bandwidth Etc…. 6 System Modeling Languages Past efforts to create System Modeling Languages E.g. Bond Graphs (1960), IDEF (1981), etc… Regardless of the System Modeling Language being developed and used they share the common features: Domain agnostic Ontology https://en.wikipedia.org/wiki/Ontology_engineering Defines the entities that are allowed to exist and be described How these entities can be grouped, related to a hierarchy and subdivided Constrains the universe of concepts that can be represented in the language Semantics https://en.wikipedia.org/wiki/Semantics Describes the meaning of the entities allowed by the ontology Relationship between signifiers (e.g. words, symbols …) and their denotation Syntax https://en.wikipedia.org/wiki/Syntax Set of rules, principles and processes that govern the structure of the language and how correct “sentences” can be synthesized 7 Overview Why Systems Modeling Languages? Ontology, Semantics and Syntax OPM – Object Process Methodology SySML – Systems Modeling Language Modelica What does it mean for Systems Engineering of today and tomorrow (MBSE)? 8 Introduction to OPM In order to rigorously architect and design products need a language to describe functions, form, concepts in a consistent way • UML 2.0 • http://www.omg.org/spec/UML/2.0/ • Mainly used for software architecting • SysML 1.3 • http://www.omgsysml.org/ • Generalization to cyber-physical systems • OPM • Object-Process-Methodology • 2002, Prof. Dov Dori, Technion • ISO Standard 19450 (2015, new !) 9 Motivation for OPM Typical Product Need for a Unified Representations Representation Sketches Show functions Engineering Drawings Show function attributes UML Diagrams Show objects (operands, (Software) system components, consumables …) Show object attributes Show links Object Process Methodology is a generic system modeling language that has Example: Refrigerator been successfully applied to Systems Kenmore 2.5 cu ft Architecting of Complex Products © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 10 Ontology of Object Process Modeling Object: that which has the potential of stable, unconditional existence for some positive Object duration of time. Objects have State states. Form is the sum of objects Process: the pattern of transformation applied to one or Process more objects. Processes change states. Function emerges from processes All links between objects and processes have precise semantics 11 OPM: Goods and Services Goods are objects Services are processes Products With every product good object, there is an implicit process Service Goods process object which is linked to value With every product Implicit Implicit object process service process, there is always an implicit object Product/systems always come in object-process pairs, and value is always linked to process 12 Structural Links in OPM Standby Power System Structural Links Link Objects to Objects AC Unit Is related to … AC Drive PWB “powers” Tagged link (suppressed process) Reset Switch Outlet Decomposes to, aggregates to Inlet Is characterized by, exhibits Main LVPS Specializes to, generalizes to Main Switch Instantiated to, belongs to the class of Outlet PSW 13 Processing Processes Defined: A process is the pattern of transformation applied to one or more objects Cannot hold or touch a process - it is fleeting AC Power Switching Generally creation, change, or destruction resultee object operand (its states are affected by the process) consumee DC Power A process relies on at least one object in the pre- Generating process set A process transforms at least one object in the pre- process set A process takes place along a time line Interlock Status Detecting A process is associated with a verb Express processes in Gerund form: ____ing 14 Process and its Links main switch A process is associated with a verb and stateless There is a family of 7 types of links from process to object A process can change the states of its operand(s) through input and output links Main Switch Operator Here Person Transporting There Main Switch State Transporting changes a Switching person from here to there on off 15 Summary Object-Process Links Here P changes O (from state A to B). Person Transporting There P affects O (affectee) Person Transporting P yields O (resultee) Emissions Transporting P consumes O (consumee) Energy Transporting P is handled by O (agent) Operator Transporting P requires O (instrument) Vehicle Transporting Enough P occurs if O is in state A Money Purchasing None * * conditional link also shown as c 16 High Level OPM of a Car Government Driver Passengers Cargo Regulations Fuel Location Owner A B Emissions Value Safety Automobile Valuing Price Transporting x(1): FC Powertrain Towing x(2): ED Chassis f(3): TC This view shows all main x(3): WT elements of the car as a Propelling x(4): WB product system: f(4): FE -objects x(5): GC Body f(5): AC - operands x(6): HT Housing - instruments f(1): PV x(7): LT - consumees, Wheels f(2): CV resultees x(8): TW - operator x(9): TD -processes -attributes Design Parts and Internal Functional Variables Assemblies Functions Attributes -x: design variables -f: functional behavior 17 Managing Complexity in OPM OPM has three mechanism for managing system complexity: unfolding/folding is used for refining/abstracting the structural hierarchy of an object; in-zooming/out-zooming exposes/hides the inner details of a process within its frame; state expressing/suppressing exposes/hides the states of an object. zooming out-zooming 18 operand “Level 0” owns Food value-related OPM of derives attribute value Refrigerator Shelf Life from Owner 7 days beneficiary primary value Temperature delivering process product system 21oF Refrigerator Extending primary operating Thermostat process super-system Setting Operating Exterior Air Interior o 21 F Air sets sets Temperature operator Waste Operator Electrical Convecting 70oF Heat Power resultee consumee 19 expansion valve Sub-Functions from Carnot Condensing ExpandingCycle Compressing Evaporating Internal Processes are governed by Physics. © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 20 Refrigerator: Functional Level -1 (4) Decomposition Level -2 (15) Operating Cooling Powering Expanding Grounding Evaporating Protecting Compressing Supplying Condensing Regulating Absorbing Sensing Supporting Switching Opening Setting Closing Retaining Connecting 21 OPM of Refrigerator Level -1 System Boundary Power Compressor Supply Powering Electrical Power Power Internal on off Operand Thermostat Refrigerant Regulating Condenser Freezer Pressure Door Evaporator Cooling Temp Door Temp Supportin Exterior g Waste Air Heat Cabinet Heat Temp Hinge Value Food Interior Operand Convecting Convecting Air Temp 22 Generic System OPM OPMs of most complex opto-mechanical systems look like this Value-Delivering Outputs Beneficiary Power Processes Operand (Customer) Supporting Processes Specialized Processes Powering Value-generating Connecting Attributes Value-Related Controlling Output Operator Non-Value- Added Outputs Raw Inputs 23 How to generate a System OPM Top-Down Start with the stakeholder(s) (customer in mind) Map value delivery process(es) at Level 0 Get to greater levels of detail in layers This is system/product architecting ! Reduce Ambiguity Focus Creativity Manage Complexity Bottom-Up Decompose form of existing product or design (product dissection): Parts List/BOM Generate an initial product decomposition Assign processes to elements of form Complete initial OPM and iterate This is reverse engineering ! 24 OPCAT Demo OPCAT is a Java-based software to generate OPM Models © Dov Dori. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.