1 Ontological Foundations For SysML Henson Graves September 2010

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

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 … Long history of attempting to use formal methods for engineering, with mixed success, often too hard to use, doesn’t scale Develop design specifications Check integration design consistency Perform integration tests Verify that implementatio n realizes specifications Perform verification tests Verify product satisfies requirements Design Implementation Test & Verification Deployment Requirements Develop requirements specifications Check specification consistency 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

5 DesignBuild Support WBS Partition Design for Implementation As Built Design As Maintained Design 4 Check Line 5 Impatient Skier 6 Line 7 Lift 1 9 Ski 8 Lift 2 10 Go Home 2 Rush Time 3 Last Skier Architecture Decomposition Size And Complexity Put Bounds On Manual Analysis 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: Paper in OWL Experiences and Directions 2008 n 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?

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

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

11 Yvonne Bijan and I Have a SysML Model And a Proof That All Implementations Of Are The Same The two diagrams which are part of the water model show both the parts structure and the bond connection  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 … 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 Constraints used to generate 3D visualization  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

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