1. A Framework for Nuclear Software (NuFA)
Seo Ryong Koo
Korea Advanced Institute Science and Technology

2. Contents Background NuFA Specification Language Architectural Layer
Tasking Layer
Computation Layer
Discussion
Appendix: AMS modeling

3. Background
Approach for Easy Inspection and Effective Use of Formal Method
Traceability Analysis
Structural Analysis
Formal Specification
Document Analysis
Webpage Supporting

4. 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

5. 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.

6. 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

7. 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

8. 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

9. 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.

10. 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 (<)

11. NuFA - Architectural Layer
Architectural Layer View

12. NuFA - Architectural Layer
The textual format

13. 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

14. NuFA – Tasking Layer

15. 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)

16. 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.

17. NuFA – Computation Layer
First level
Second level
Third level

18. 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

19. NuFA – Computation Layer
NS charts
CASE statements
Simple statements
FOR statements
IF statements

20. 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

21. 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

22. Appendix: AMS Modeling

23. Appendix: AMS Modeling

24. Appendix: AMS Modeling

25. Appendix: AMS Modeling