Automation for System Safety Analysis Jane T. Malin, Principal Investigator Project: Automated Tool and Method for System Safety Analysis Software Assurance Symposium September, 2007 Complex systems typically fail because of the unintended consequences of their design, the things they do that were not intended to be done. - M. Griffin, System Engineering and the “Two Cultures” of Engineering, March 28, 2007

SAS 07 Automation for System Safety Analysis Malin 2 Problem Need early evaluation of software requirements and design –Assess test and validation plans Assess system failures and anomalous conditions that may challenge software in system integration testing Identify software-system interaction risks –Identify requirements gaps –Perform virtual system integration tests prior to software- hardware integration Benefits –Reduce software-system integration risks early –Reduce requirements-induced errors and rework in later development phases –Improve efficiency and repeatability of analyzing system and software risks Reduce time spent reanalyzing when specifications and designs change –Reduce contention for software-hardware integration laboratory resources

SAS 07 Automation for System Safety Analysis Malin 3 Technical Approach Systematic semi-automated analysis for early evaluation and rapid update –Capture model of the controlled system architecture Abstract physical architecture models with subsystems, functions, interfaces, connections –Extracted directly from requirements and design text and data –Capture risks and hazards in model Constraints, hazards, risks from requirements and design Risk and failure libraries –Analyze model and risk data to identify relevant risks and constraints Analyze and simulate risk propagation in the system Use operational and off-nominal scenarios and configurations –Identify possible test scenarios for virtual system integration testing

SAS 07 Automation for System Safety Analysis Malin 4 Relevance to NASA This work leverages component tools that have been used in NASA applications Goal: Integrate and enhance these tools for software assurance during requirements and design phases Project test case is NASA Constellation Launch Abort System (LAS)

SAS 07 Automation for System Safety Analysis Malin 5 Extend and Integrate Existing Technology Requirements and Constraints Text Risks & Mitigations Physical/Functional Architecture Models Discrete Time Simulation Model Extraction Tool: Model Parts, Interfaces, Risks, Scenarios Library Components, Connections, States & Risks Functional Diagrams Aerospace Ontology Taxonomy, Thesaurus, Classes, Synonyms Modeling Tool: - Map -Connect - Visualize - Embed problems and states Analyze and Simulate: - Identify interaction-risk pairs - Estimate severity in nominal and fault scenarios - Investigate influence of timing Reports Pairs, Paths, Risky Scenarios, Test Cases for Virtual System Integration Testing Virtual System Integration Lab (VSIL) Inputs  Extraction  Modeling  Analysis  Simulation  Testing Interaction Model

SAS 07 Automation for System Safety Analysis Malin 6 Extraction Tool and Nomenclature Reconciler Extractor –Extract model parts from requirements text and data from functional analysis and threat/risk analysis –Semantic parsing for text analysis and word/phrase classification –Extract operational scenarios from functional analysis data Aerospace Systems Library and Ontology –Classes of model elements with properties and defaults –Taxonomy with synonym lists, for parsing and mapping to types of model elements –Extensive problem taxonomy and thesaurus that includes hazard types from Constellation Hazard Analysis handbook Current NASA use: Semantic text mining to classify JSC Discrepancy Reports (DRs) for trend analysis –Discrepancy Reports describe mechanical, electrical, software and process discrepancies in engineering and operating NASA- furnished equipment

SAS 07 Automation for System Safety Analysis Malin 7 Discrepancy Report Analysis Tool Cross-Cutting Teams Receive Subsets of DRs in Excel File and Browsers Extract DRs from Database Analyze text in each DR Problem Description Identify categories of problems described Sort DRs into subsets for cross- cutting teams: Mechanical, Electrical, Software, Process, Other Browsers for Each Cross-Cutting Team, with links to Database Filterable Excel File

SAS 07 Automation for System Safety Analysis Malin 8 Model-Based Safety Analysis Case Model extraction and hazard analysis were demonstrated in 2005 –Case: Generic unmanned spacecraft; concerns about transmitter noise –Requirements from SpecTRM and risks from Defect Detection and Prevention (DDP) Tool –Reference: J. T. Malin, D. R. Throop, L. Fleming and L. Flores, “Transforming Functional Requirements and Risk Information into Models for Analysis and Simulation,” 2005 IEEE Aerospace Conference Proc., March 2005.

SAS 07 Automation for System Safety Analysis Malin 9 Reconciler Information Extractor Requirements Risks and Mitigations Parse and Extract: Model Parts Interfaces Vulnerabilities Threats/Risks Mitigations Scenarios Functional Diagrams XML- Structured Data Aerospace Ontology Classes, Synonyms

SAS 07 Automation for System Safety Analysis Malin 10 Reconciler Tool Extracts Model Parts from Text Parses the Process and Requirements sentences from SpecTRM or Cradle Extracts functions and objects Classifies functions (uses Aerospace Ontology) Formats the parsed knowledge –In XML format or OWL format Passes results for mapping into models OWL XML

SAS 07 Automation for System Safety Analysis Malin 11 Requirements Model ( Shift Info ) Operation/Function: Transfer (“Downlink”) Agent/contributor: ? Affected Operand: Information Operand Source: ? Operand Destination/Goal: ? Path Type: Information Effect value/measures: “Successful” … Problem Model (Failure of Function ) Problem: Failure of function (“Failure”) Agents/contributors: “Transmission Subsystem, Transmitter…” Impacted Entity: “Telecom Subsystem” Impacted Objective (link to): “Downlink Successful” … Reconciler Tool Extracts Risks RAP or ARM Risk Analysis and Matrix DDP Analysis and Visualization of Risks, Mitigations and Costs Mitigation Model ( Replace ) Function Type: Replace (“Redundancy”) Replaced: “Transmitter” Replacement: “Transmitter Spare” Counteraction Type: Recover Counteracted Problem (link to): “Telecom Sub… Failure… Transmitter” … Objective: “Downlink successful” Risk: “Telecom Subsystem Failure: Transmission: Transmitter” Mitigation: “Redundant Systems: Transmitter” Transmitter Failure Mitigation: Redundant Transmitter Telesub: Failure (Transmission sub: Transmitter)

SAS 07 Automation for System Safety Analysis Malin 12 Modeling and Analysis Tools Hazard Identification Tool (HIT) identifies threats and risks –Model mapper and developer –Hazard path analyzer –Model diagram visualizer –Least mature tool in the suite Hazard Identification Tool was demonstrated in SpecTRM spacecraft case –Use Reconciler output to develop interaction architecture and risk model –Identify pairs that are not intended to interact Hazard sources Sensitive or vulnerable objects or functions –Analyze paths between pairs and estimate severity

SAS 07 Automation for System Safety Analysis Malin 13 Hazard Identification Tool Architecture Visualizer Library Components Functions Problems Extracted Model Data (XML from Reconciler) Modeler: - Map - Connect - Embed problems and states Aerospace Ontology Classes, Synonyms Path Analyzer: - Find pairs - Search graph of paths in scenarios - Estimate Severity Report Pairs, Paths Risky Scenarios, Test Cases

SAS 07 Automation for System Safety Analysis Malin 14 Modeler: Each Requirement Provides Pieces of the Architecture [C.1] Telecommunication Subsystem (Telesub) [C.1.1] The CDHC sends the TeleSub a compressed picture. [FG.1] [TeleSub C.1.4] [C.1.2] The CDHC sends the TeleSub telemetry. [FG.2] [FR.1] [FR.5] [TeleSub C.1.5] [C.1.3] The CDHC sends In View of Ground alerts to the TeleSub. [DP.5.6] [TeleSub C.1.6] [C.1.4] The CDHC receives plan files from the TeleSub. [FR.3] [TeleSub C.1.3] [C.1.5] The CDHC receives ground commands from the TeleSub. [FR.3] [TeleSub C.1.2] [C.1.6] The CDHC receives the TeleSub operating state from the TeleSub. [DP.5.5] [TeleSub C.1.1] … [C.2] Camera Subsystem [C.2.1] The CDHC sends the Camera a "take picture" command. [FG.2] [FR.1] [FR.3] [C.2.2] The CDHC sends the Camera x, y and z gimballing coordinates. [FG.2] [FR.1] [FR.3] [C.2.3] The CDHC sends a turn on command to the Camera. [DP.5.3] [H Constraint 1.1.4] [C.2.4] The CDHC sends a turn off command to the Camera. [DP.5.3] [C.2.5] The CDHC receives a compressed picture file from the Camera. [FG.1] [FG.2] [FR.1] … [C.4] Attitude Determination Subsystem [C.4.1] The CDHC receives an In View of Ground alert from the ADS. [DP.5.6] [ADS] [C.4.2] The CDHC receives the ADS operating state from the ADS. [DP.5.5] [ADS] Requirements Model (Shift Info) Function Type: Transfer (“Send”) Agent/Contributor: Subsystem (“CDHC”) Affected Operand: Information (“Telemetry”) Operand Source: Subsystem (“ CDHC”) Operand Destination/Goal: Subsystem (“ Telesub”) Path Type: Information … CDHC Fn: Send Telesub Telemetry Physical/Functional Architecture Fragment SpecTRM: Spacecraft Command and Data Handling Computer (CDHC) Send/Receive Requirements

SAS 07 Automation for System Safety Analysis Malin 15 Modeler: Architecture Model and Visualization of a Set of Requirements [C.1] Telecommunication Subsystem (TeleSub) [C.1.1] The CDHC sends the TeleSub a compressed picture. [FG.1] [TeleSub C.1.4] [C.1.2] The CDHC sends the TeleSub telemetry. [FG.2] [FR.1] [FR.5] [TeleSub C.1.5] [C.1.3] The CDHC sends In View of Ground alerts to the TeleSub. [DP.5.6] [TeleSub C.1.6] [C.1.4] The CDHC receives plan files from the TeleSub. [FR.3] [TeleSub C.1.3] [C.1.5] The CDHC receives ground commands from the TeleSub. [FR.3] [TeleSub C.1.2] [C.1.6] The CDHC receives the TeleSub operating state from the TeleSub. [DP.5.5] [TeleSub C.1.1] … [C.2] Camera Subsystem [C.2.1] The CDHC sends the Camera a "take picture" command. [FG.2] [FR.1] [FR.3] [C.2.2] The CDHC sends the Camera x, y and z gimballing coordinates. [FG.2] [FR.1] [FR.3] [C.2.3] The CDHC sends a turn on command to the Camera. [DP.5.3] [H Constraint 1.1.4] [C.2.4] The CDHC sends a turn off command to the Camera. [DP.5.3] [C.2.5] The CDHC receives a compressed picture file from the Camera. [FG.1] [FG.2] [FR.1] … [C.4] Attitude Determination Subsystem (ADS) [C.4.1] The CDHC receives an In View of Ground alert from the ADS. [DP.5.6] [ADS] [C.4.2] The CDHC receives the ADS operating state from the ADS. [DP.5.5] [ADS] Note: CDHC is Command and Data Handling Computer Physical/Functional Architecture Model

SAS 07 Automation for System Safety Analysis Malin 16 Modeler: Seed the Spacecraft 1 (SC1) Model with Problems and Mitigations Libraries of objects (components) and functions –Typical components and operating modes –Typical functions and failures –Typical output that may be a problem –Typical sensitivities and tolerances –Typical mitigations Manual additions to model –Add spare transmitter (xmitter) –Transmission performance (rate) degradation due to noise –CDHC Comm Controller controls mitigation: switch to spare transmitter –Add Comm Network, Ground data components –Remove Reaction Control System (RCS) and camera –Add Power (PwrSpply) and Thermal Control (ThermalSys) subsystems, with new risks and mitigations ThermalSys is noise source (when on) Power lines can transmit noise

SAS 07 Automation for System Safety Analysis Malin 17 Path Analyzer: Find Potential Interaction Problems 1.Find matching pairs of components (hazard source-vulnerable sink) 2.Find system interaction paths that permit hazards to impact sensitive components and functions 3.Estimate local and integrated system hazard impact severity

SAS 07 Automation for System Safety Analysis Malin 18 Path Analyzer: Incremental Quick Look Approach Simple early threat analysis, refined as design information becomes available –Identify risky matching pairs from component or function vulnerabilities, threats and hazards –Search for paths between pairs along connections or dependencies –Make search dependent on configuration information, with changeable configuration and operational states Estimate impact severity from local estimates of severity

SAS 07 Automation for System Safety Analysis Malin 19 Simulator: CONFIG Simulation Tool to Assess Timed Scenarios NASA experience with CONFIG hybrid discrete event simulation tool: Used for software virtual validation testing for day manned Lunar Life Support Test Software: Intelligent control for gas storage and transfer Testing: Simulated failures and imbalances that would not be tested in hardware-software integration Too slow to develop, too expensive, too destructive Results: Identified software requirements deficiencies

SAS 07 Automation for System Safety Analysis Malin 20 Add Timing to Selected Scenarios and Narrow Potential Problem Set Model data Integrated Architecture Model Mapped Timed Simulation Model Log/Report Specifications Scenario Scripts Map components and connections Reuse scenario scripts and report specifications

SAS 07 Automation for System Safety Analysis Malin 21 Virtual System Integration Lab (VSIL) Triakis has used VSIL in >25 avionics verification projects Models and problem configurations for new tests and test suite models Models and Test Definitions DE: detailed executable, the simulation of the embedded controller hardware ES: executable specifications V&V: verification and validation

SAS 07 Automation for System Safety Analysis Malin 22 Accomplishments: First 9 Months Drafted Concept of Operations Enhanced tools Completed a simple integration of tool functions, inputs and outputs –Based on SpecTRM-style requirements text Selected Constellation Launch Abort System Case –Gained access to Cx Windchill materials 9/07 Takes time, but requirements may now be mature enough

SAS 07 Automation for System Safety Analysis Malin 23 Concept of Operations Drafted and iterated a draft Concept of Operations Document with Safety and Mission Assurance (S&MA) (Due 12/07) –Data flow diagram shows use of tools to support S&MA software processes and virtual system integration testing

SAS 07 Automation for System Safety Analysis Malin 24 Tool Enhancements Refined Reconciler parsing and extraction capabilities Re-implemented Hazard Identification Tool functions for constructing hierarchical models from extracted model parts –No longer uses Protégé –Uses elements of CONFIG simulation tool for automatic and manual model construction and visualizing architecture models Re-implemented risk path analyzer code, to make planned extensions feasible

SAS 07 Automation for System Safety Analysis Malin 25 Aerospace Ontology Library Objects Enhanced Aerospace Ontology class objects for modeling risks and qualitative dependency relationships –General for multiple types of influences among entities and functions/actions Capability, integrity/reliability, performance timing and quality or controllability Influencing Factor Relationships –Positive-Negative (signed) relation to influenced variable or problem –Importance (degree of worst-case impact) –Likelihood (probability of occurrence of factor) –Cross-reference to Requirements and Constraints

SAS 07 Automation for System Safety Analysis Malin 26 Aerospace Ontology Action Primitives Enhanced Aerospace Ontology taxonomy for straightforward mapping to primitives used in path analysis Place/Arrange –Move + EntityOperand + Path Transport + SourcePlace + DestinationPlace –Change “Owner” Transfer + EntityOperand + Source + Sink Input/Output + EntityOperand –Output »Emit (Active-Output) »Release (Passive-Output) –Take-In »Input (Active Take-In) »Receive (Passive Take-In) Process –Transform + EntityOperand + Parameter Phase change, change in composition… –Change Position on a Scale + EntityOperand + Parameter Increase Decrease Control –Regulate + EntityOperand + Parameter

SAS 07 Automation for System Safety Analysis Malin 27 Simple “Hello World” Architecture Case CDHC Telesub Data CSRL Spacecraft CDHC: Command and Data Handling Computer Telesub: Telemetry subsystem –Extracted model parts from small set of requirements (2 components, 1 connection) –Defined output specifications for XML model files from HIT for VSIL –Expanded “Hello World” example case definition to include risk information in components

SAS 07 Automation for System Safety Analysis Malin 28 Potential Applications Visualize integrated requirements Evaluate completeness and consistency of requirements and risk Quickly reanalyze each revision of requirements and risk Validate failure modes and effects analysis (FMEA) and fault trees Validate and test early with low-fidelity simulation

SAS 07 Automation for System Safety Analysis Malin 29 Next Steps Complete first version of Launch Abort System case and evaluate – Text extraction from requirements and risks – Model construction and visualization – Model analysis to identify interaction risks and test configurations for virtual software integration testing Complete Concept of Operations Enhance tool suite capabilities, integration and user interfaces –Achieve Technology Readiness Level (TRL) 6 –Prepare for other uses for Constellation software assurance

SAS 07 Automation for System Safety Analysis Malin 30 References J. T. Malin and D. R. Throop, “Basic Concepts and Distinctions for an Aerospace Ontology of Functions, Entities and Problems,” 2007 IEEE Aerospace Conference Proc., March J. T. Malin and L. Fleming, “Vulnerabilities, Influences and Interaction Paths: Failure Data for Integrated System Risk Analysis,” 2006 IEEE Aerospace Conference Proc., March T. L. Bennett and P. W. Wennberg, “Eliminating Embedded Software Defects Prior to Integration Test,” CROSSTALK: The Journal of Defense Software Engineering, December J. T. Malin, D. R. Throop, L. Fleming and L. Flores, “Transforming Functional Requirements and Risk Information into Models for Analysis and Simulation,” 2005 IEEE Aerospace Conference Proc., March D. Throop, “Reconciler: Matching Terse English Phrases,” Proceedings of 2004 Virtual Iron Bird Workshop, NASA Ames Research Center, April, J. T. Malin, D. R. Throop, L. Fleming and L. Flores, “Computer-Aided Identification of System Vulnerabilities and Safeguards during Conceptual Design,” 2004 IEEE Aerospace Conference Proc., March J. T. Malin, L. Fleming and T. R. Hatfield, “Interactive Simulation-Based Testing of Product Gas Transfer Integrated Monitoring and Control Software for the Lunar Mars Life Support Phase III Test,” In Proceedings of SAE 28th International Conference on Environmental Systems. SAE Paper No , 1998.