Ontological Foundations For SysML

1. Ontological Foundations For SysML Henson Graves September 2010

2. INCOSE IW09 MBSE Workshop INCOSE MBSE Roadmap Design optimization across broad trade space Cross domain effects based analysis System of systems interoperability Reduced cycle times MBSE Capability June 15, 2008 Institutionalized MBSE across Academia/Industry This talk fits here Distributed & secure model repositories crossing multiple domains Defined MBSE theory, ontology, and formalisms Well Defined MBSE Refer to activities in the following areas: Architecture model integrated with Simulation, Analysis, and Visualization Maturity • Planning & Support • Research • Standards Development • Processes, Practices, & Methods • Tools & Technology Enhancements • Outreach, Training & Education Matured MBSE methods and metrics, Integrated System/HW/SW models Emerging MBSE standards Ad Hoc MBSE Document Centric 2010 2010 2020 2025

3. Outline • Why is an MBSE reasoning formalism so important • Lessons from applying OWL to engineering applications • Steps toward integrating OWL reasoning with SysML

4. Reasoning Is Required Multiple Places In The Systems Engineering Process Deployment Requirements Design Test & Verification Implementation Develop requirements specifications Develop design specifications Perform integration tests Perform verification tests Check specification consistency Check integration design consistency Verify that implementation realizes specifications Verify product satisfies requirements Produced by Engineering Tools Produced by Reasoning Tools • Are requirements consistent • Are implementations feasible • Is design sufficiently detailed for implementation • Can an implementation satisfy design requirements • Do proposed modifications stay within design constraints • … Long history of attempting to use formal methods for engineering, with mixed success, often too hard to use, doesn’t scale

5. Design Build Support 2 3 Rush Time Last Skier 4 5 Check Line Impatient Skier 6 Line 7 8 Lift 1 Lift 2 9 Ski 10 Go Home Size And Complexity Put Bounds On Manual Analysis WBS Partition Architecture Decomposition As Built Design As Maintained Design Design for Implementation 150 15000 1500 Many enterprises use modeling extensively but the result is an enormous collection of non-integrated models - Situation is worse than in document centric development

6. Where Does One Look For Formal Logical Foundation For Modeling Systems: OWL • Designed for conceptual modeling • represents more than 20 years of research • Extensive experience model complex physically structured systems in the life sciences and medicine • Logic based modeling language • Optimized reasoning algorithms • designed so as to be decidable (arbitrary queries can be answered) • W3C language standard with tool support • Designed so as to allow for extensibility … its clear that OWL and UML/SysML have significant overlap

7. Ian Horrocks Helped Me Develop An OWL Air System Ontology in Protégé To Answer: • Can OWL provide semantic foundation and integration for MBSE • Could OWL work where other approaches have failed? • Can ontologies capture meaning of concepts independent of interpretation by subject matter experts? • Can automated reasoning be used to check design properties such as consistency and conformance with specification? Paper in OWL Experiences and Directions 2008

8. The OWL Experience • One can build OWL ontologies to represent static structure of systems • Used reasoning to verify design consistency with requirements and other questions • We made extensive use of an Upper Ontology • Some requirements not (easily) expressible OWL • Weight of product is sum of weights of components • Behavioral requirements • Representing a “detailed design” in OWL is difficult • (where all valid implementations have the same parts structure and connection relationships) The experience led me to focus on how to represent detailed designs, first in OWL and its extensions, and then in SysML

9. two fingers sharing distal phalange Hands with 500 fingers Non-connected fingers as part of hand Which Models (Ontologies) Have The Property That All Valid Implementations Have The Same Structure? Model Rule out implementations with Then can argue from a specific implementation to any implementation

10. How Can a Model Be Characterized So All Implementations Have The Same Structure? Used To A Water Model • Generate 3D Visualization of implementation • Answer questions about mass, size, geometrical shape, … Develop examples and generalize

11. Yvonne Bijan and I Have a SysML Model And a Proof That All Implementations Of Are The Same • This is a prototypical design analysis/verification problem • If all implementations are the same you can calculate or measure weight of individual molecule • Another version of problem is when is a design sufficiently complete that it can be implemented The two diagrams which are part of the water model show both the parts structure and the bond connection … we are building the models directly in SysML but have to go outside SysML for reasoning

12. We Had To Add Some Additional Axioms For Water That May Be Implicit In SysML Issues arising in the proof • Does any valid implementation of Water have exactly three atoms Language concepts and constructs match modeling domain • Maybe it is implied by the SysML spec, but we had to add it • The covalent bond is a SysML connection between parts • We added the equation hasHydrogenAtom.covalentBond = hasOxygenAtom • We also had to make assumptions about restrictions of properties … we have (we think) a general concept of structural template that can be validated by SysML tools

13. SysML Has Language Constructions Not In OWL • Variables & operations • Constraints • Behavior • Role properties, e.g., part properties and other component properties OWL reasoning can be made to work where languages overlay, but the reasoning requires extension for full SysML Constraints used to generate 3D visualization

14. Conclusions: Providing SysML With A Logical Foundation is feasible and it … • Enables engineers to work in a good user friendly language integrated with valid reasoning tools • Engineers are able to employ benefits of logic without having to learn special logical language syntax • Provides better integration with simulation • Provides a check on expressiveness and coherence • Provides potential language candidate extensions for SysML and OWL2 There is a strong case that OWL and SysML can be unified with benefits to both

15. Next Steps • Develop SysML use cases for inference • Develop rules to translate SysML to an extended OWL2 • Export SysML to reasoner and reimport results • Develop template validation code for SysML tools • Verify SysML logic retrofit is computationally tractable