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IAEA TM-2005 Chatou. Need for Probabilistic Safety Assessment of Software Increasing importance of software for probabilistic methodsAverage age of NPP's in Europe > 15 yearsExtension of plant life-time (USA, Japan)Backfitting and modernisation of analog technique I
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1. IAEA Technical Meeting 2005 Complexity Measurement of Software in Digital I&C-Systems for the Quantification of Reliability 15. September 2005
J. Märtz
A. Lindner
ISTec GmbH, Forschungsgelaende, D-85748 Garching n. Munich
2. IAEA TM-2005 Chatou Need for Probabilistic Safety Assessment of
Software
Increasing importance of software for probabilistic methods
Average age of NPP’s in Europe > 15 years
Extension of plant life-time (USA, Japan)
Backfitting and modernisation of analog technique I&C-Systems by digital I&C- Systems
Safety assessment of new digital I&C-Systems
3. IAEA TM-2005 Chatou Reliability-Growth Models
Regulations by Standards e.g. DO-178B (Avionics)
Dynamic-Flowgraph-Methodology (DFM-Method)
Software Reliability Prediction Models
4. IAEA TM-2005 Chatou Software Reliability Prediction Models
Basic Software Attributes (LOC, Operations, Operands)
Development Data
Evaluation of Operational Experience of comparable Systems (e.g. Air Force)
MIL-HDBK-338 B
NASA (Technical Memorandum 104799)
6. IAEA TM-2005 Chatou Concept
Basis
Common generic structure of Digital I&C Systems Methodology
System-Complexity as crucial factor for system-reliability und –availability
Characteristics
Concentration on system-inherent, objectively identifiable data
Usage of system-specific features relevant for reliability
Correlation between System-Complexity and System-Reliability via
Data-Collections (e.g. COMPSIS)
Engineering Judgement of experts
BBN-Method (Bayesian-Belief-Network)
7. Digital I&C Systems Structure
8. IAEA TM-2005 Chatou Common Properties of Digital I&C-Systems
Graphic based specification of functionality
Logic circuit of basic elements
Code generation on basis of graphical specification
Representative Digital I&C-Systems
TELEPERM XS
TRICON
COMMON Q
KNICS (in development)
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Evaluation and Measurement of the Functional Blocks (FB)
Evaluation and Measurement of the Logic Diagrams (LD)
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Types of elementary functions implemented as Functional Blocks:
Logic or arithmetic functions such as OR, AND, ADD etc.,
Basic I&C functions e.g for implementing a comparison or an interpolation curve,
Specific functions such as ramp generator or sorter
11. IAEA TM-2005 Chatou Determination of a FB-Complexity-Matrix
Limited and fixed set of FB's, on basis of which all applications are constructed (designed),
Evaluation of the Functional Blocks, independent of a specific application
Black-Box View
User point of view / based on Manuals and Documentation (also feasible if Source-Code of Functional Blocks not available)
White-Box View
Based on Source-Code / generated by Static Analysis Tools
12. IAEA TM-2005 Chatou Black Box View
derived from documentation of FB‘s (e.g. User Manuals)
follows definition of psychological complexity (Sullivan): “In general usage, complexity denotes the degree of mental effort required for comprehension“.
Features
Signals (Number and type: analog-binary / Input-Output-Message)
Parameters (Number and Type: changeable, unchangeable, derived)
Internal Memories (Internal states)
Resources needed (Time, Memory)
Runtime-Modes (Initializing, Parameter-Setting, Computing)
Status processing of signals (Signal-status: erroneous, test, o.k.)
Failure-Handling (Failure propagation, Failure barriers)
Return-Codes
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17. IAEA TM-2005 Chatou Complexity Vector for Logic Diagrams
Components
I/O-Connections (Adjacency)
Number of input signals / output signals
Volume
Number of FBs
Interconnection V(LD)
V(LD) describing the logical (functional) complexity
Internal memories
Describing the set of internal states
Parameters
Describing the modifiability of a system
18. IAEA TM-2005 Chatou Interconnection V(LD)
| VB(Si) |
V(LD) = S
Si | BLD |
Si all the individual output signals of the Logic Diagram
VB(Si) set of elementary functional blocks that are involved in the computation of the output signal Si
BLD set of functional blocks making up the Logic Diagram
| | cardinality (number of elements of a set)
19. IAEA TM-2005 Chatou
Applicable to any generic, graphic-based digital I&C system based on elementary functions
Simple (Graph-based Definition)
Scalable to the internal [0, 1] due to 1 = V(LD) = N (output signals)
Basically independent of FB-Complexity
Modular with respect to Single Signal, Processor Allocation, FB-Complexity
Comprises implicitly important Complexity Measures for Graphs:
Structural Complexity (K/N)
Hierarchical Complexity (Levels)
Branching Complexity SVi
Cyclomatic Complexity (Mc Cabe)
20. Parameters (Modifiability / Flexibility)
Parameter (LD) = S Parameter (FBi)
FBi
Internal Memories (Internal States)
Internal Memory (LD) = S Internal Memory (FBi)
FBi
IAEA TM-2005 Chatou
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22. IAEA TM-2005 Chatou Complexity Vector for I&C-Function-Example:
Input Signals 9
Output Signals 12
Functional Blocks 20
Interconnection V(LD) 4,95 ? [1;12]
Scaled Interconnection 0,36 ? [0;1]
Internal Memories 12
Changeable Parameters 64
(49 parameters just for one single elementary FB dedicated to the definition of a characteristic curve)
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