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A Framework for Nuclear Software (NuFA)
Seo Ryong Koo Korea Advanced Institute Science and Technology
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Contents Background NuFA Specification Language Architectural Layer
Tasking Layer Computation Layer Discussion Appendix: AMS modeling
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Background Approach for Easy Inspection and Effective Use of Formal Method Traceability Analysis Structural Analysis Formal Specification Document Analysis Webpage Supporting
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Background Current Status of NuSCR NuSCR (ver 0.1) (ver 0.2) NuFA
Elimination of several limitations Enable port NS charts Three layers Updated NS charts Elimination of partial data flow Deleting SDT
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Background NuSCR Approach
Specification language and Framework and Verification environment in Nuclear Fields Three phases The NuSCR editor provides an environment for specifying a nuclear controller system and it stores the system in a file. The stored file is translated into the PVS or SAL specification language. The translated specification is verified by PVS theorem prover or SAL model checker.
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Background Limitations of NuSCR ver 0.1
Lack of traceability between Functional Requirement and NuSCR Too complex to understand NuSCR Unfamiliar to nuclear engineer Need to simultaneously consider users’ viewpoints and analyzers’ viewpoints
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Background Characteristics of Nuclear Fields
Extreme safety-critical system The engineers have their peculiar tastes and tendencies. To like simple notation To easily understand To concentrate on traceability between documents The duplication of a system is common. Need to write formal specification
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NuFA Specification Language
NuSCR version 0.3 Stands for Framework for nuclear software Is a framework and a specification language for describing and verifying a control system for both nuclear engineers and software developer in nuclear fields. Is based on Parnas’ four-variable model (environment, input/output device, software) Is composed of three layers Architectural layer Tasking layer Computation layer
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NuFA Specification Language
Different from NuSCR version 0.1 Introduce three layers to specify a system Provide a larger view of a system Add NS charts to specify the lowest level of computation Eliminate partial data flow for array element Delete Structured Decision Table A control flow, which choose whether execute a module or not, is changed into enable port.
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NuFA - Architectural Layer
System configurations The layer is described for duplication of components and external interface to/from operator, sensors, actuators, and other systems. Expressions Double solid line box component Small white box input port Small black box output port Binding operator (->) Instantiation of component (<)
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NuFA - Architectural Layer
Architectural Layer View
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NuFA - Architectural Layer
The textual format
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NuFA – Tasking Layer Information about scheduled units
A task is a scheduling unit which takes time to execute. A component in an architecture level is decomposed of tasks. The frequency of invoking is specified. Expressions A solid line box task [period] task period Input / output port
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NuFA – Tasking Layer
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NuFA – Computation Layer
Computation procedures Supports programming-in-the-small A component in this layer is a module which is a computation unit. The module can be decomposed in a hierarchical way. Expressions Function Overview Diagram (FOD) Nassi-Schneiderman (NS) charts State Transition Table (STT)
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NuFA – Computation Layer
Function Overview Diagram (FOD) Is a similar notation to DFD Shows data flows and hierarchies among functions or groups An enable port which is written in a white circle describes an enabling condition to execute.
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NuFA – Computation Layer
First level Second level Third level
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NuFA – Computation Layer
Nassi-Schneiderman (NS) charts Was developed for describing a program module in a structured way initially in early 1970’s by Ike Nassi and Schneiderman Supports several variations Simple sequential statements If statements Case statements For statements
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NuFA – Computation Layer
NS charts CASE statements Simple statements FOR statements IF statements
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NuFA – Computation Layer
State Transition Table (STT) Is a notation for state node Support only a simple notation which does not raise bad interaction Can be incorporated within an NS charts
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Discussion It was possible to apply to CPCS and AMS successively.
Need to validate NuFA syntax and semantic in detail. How to validate NuFA specification. PVS and SAL Model checker Is NuFA specification familiar? To nuclear engineer To software developer
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Appendix: AMS Modeling
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Appendix: AMS Modeling
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Appendix: AMS Modeling
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Appendix: AMS Modeling
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