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Metrics for Fault-Tolerant Real-Time Software. Afzel Noore Computer Science and Electrical Engineering West Virginia University. September 6, 2001. Outline. Literature Review and Background Extension of Function Point Metrics Software Fault-Tolerant Structures

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slide1

Metrics for Fault-Tolerant

Real-Time Software

Afzel Noore

Computer Science and Electrical Engineering

West Virginia University

September 6, 2001

slide2

Outline

  • Literature Review and Background
  • Extension of Function Point Metrics
  • Software Fault-Tolerant Structures
  • Proposed Metrics Framework
  • Summary
  • Future Work
slide3

Why Function Point Metrics?

  • Language independent
  • Provides better design visibility
  • Useful as an estimation technique
  • Used as a measure of productivity
  • Helpful in managing change of scope
slide4

Function Point Applications

  • Prediction of the maintenance efforts
  • Measurement of size and complexity of algorithms
  • Sizing and costing individual components of software
  • Useful for checking requirements completeness
slide5

Function Point Calculation

  • Identification of the subsystem boundaries
  • Identification of data functions
  • EIF (External Interface Files)
  • ILF (Internal Logical Files)
  • Identification of transactional functions
  • EI (External Input)
  • EO (External output)
  • EQ (External Enquiry)
  • Calculation of Unadjusted Function Point Count
  • UFPC = ΣEI*w + ΣEO*w + ΣEQ*w + ΣILF*w + ΣEIF*w
  • (w is the corresponding weight assigned)
slide6

Function Point Calculation ...

  • Determination of the Value Adjustment Factor
  • VAF = (TDI * 0.01) +0.65
  • TDI is the Total Degree of Influence
  • Calculation of the Adjusted Function Point Count)
  • AFPC = VAF * UFPC
slide7

Limitations of Function Point Analysis

  • Does not provide accurate measures for real-time

software

  • The number of sub-processes in a real-time software

varies continuously

  • There are a large number of single-occurrence control

variables, which can not be counted by FPA

slide8

Full Function Point and COSMIC

In 1997, St-Pierre proposed the Full Function Points approach as an extension to the IFPUG standard to capture the functional size of real-time applications.

Common Software Measurement International Consortium (COSMIC)

Full Function Point

The COSMIC initiative draws an international team of software metrics experts to establish principles of the new measurement method based on the best features of existing IFPUG, Mark II, and FFP methods.

slide9

Evolution of Function Point Metrics

FFP1.0

FFP2.0

FFP2.1

St-Pierre 97

COSMIC 99, 2001

Mark II FPA

Mark II FPA 1.3.1

Symons 88

UKSMA 98

FPA

FPA 3.4

FPA 4.0

FPA 4.1

FPA

Albrecht 84

IFPUG 90

IFPUG 94

IFPUG 99

Albrecht 79

slide10

Extension for RT & FT Software

FFP1.0

FFP2.0

FFP2.1

St-Pierre 97

COSMIC 99, 2001

FPA

FPA 3.4

FPA 4.0

FPA 4.1

FPA

Albrecht 84

IFPUG 90

IFPUG 94

IFPUG 99

Albrecht 79

Mark II FPA

Mark II FPA 1.3.1

Symons 88

UKSMA 98

slide11

Extension for RT & FT Software

IFPUG FPA

COSMIC FFP

EFP

slide12

Design or Selection of Metamodel

Management Process – FPA

EI : External Input

EO: External Output

EQ: External Inquiry

ILF: Internal Logical File

EIF: External Interface File

Control Process – FFP

ECE: External Control Entry

ECX: External Control Exit

ICR : Internal Control Read

ICW: Internal Control Write

RCG: Read-only Control Group

UCG: Updated Control Group

slide13

Design or Selection of Metamodel...

Control Implementation – EFP

CIS: Control Implementation Structure

RDS: Redundant Data Sets

RA: Redundant Algorithms

AC: Algorithmic Complexity

VSA: Version Sequential Arrangement

TC: Timing Constraints

slide14

Characterization of Software

Control Implementation Structure

RB: Recovery Block

NVP: N-Version Programming

CRB: Consensus Recovery Block

DRB: Distributed Recovery Block

EDRB: Extended Distributed Recovery Block

RFCS: Roll-Forward CheckPointing Scheme

NSCP: N Self-Checking Programming

NCP: N-Copy Programming

RTB: Retry Block

slide15

EXTERNAL CONTROL EXIT

LA

Req.38

Req.35

Req.37

Req.79

LB

1

1

1

1

1

1

1

1

1

1

LC

Req.100:

Req.100:

Req.100:

Req.100:

Req.100:

Req.100:

Req.100:

EXTERNAL CONTROL

ENTRY

FA

Req.79 Trip

FB

FC

FD

SP1

Req.86

Req.87

SP2

Nuclear Reactor

Algorithm:

2 out of 4 Power Flux (FA,FB,FC,FD)

must be greater than High Power Flux

Set-Point (SP2).

F: Power Flux A,B,C,D.

SP: High Power Flux Set-Point

slide17

Recovery Block - Software Structure

  • BEGIN
  • ENSURE acceptance test;
  • BY Primary alternative;
  • ELSE
      • IF NOT <time-out> THEN
  • BY 2nd alternative;
  • ELSE error;
  • FI
  • ELSE
      • IF NOT <time-out> THEN
  • BY 3rd alternative;
  • ELSE error;
  • FI
slide18

Recovery Block - Software Structure ...

  • ……
  • ELSE
      • IF NOT <time-out> THEN
  • BY n’th alternative;
  • ELSE error;
  • FI
  • ELSE
  • Error;
  • END
  • Structural Complexity: O(n)
slide19

Recovery Block - Design Diversity

CIS: Control Implementation Structure

RDS: Redundant Data Sets

RA: Redundant Algorithms

AC: Algorithmic Complexity

VSA: Version Sequential Arrangement

TC: Timing Constraints

Recovery Block

Average

High

High

High

High

slide21

N Copy Programming - Data Diversity

CIS: Control Implementation Structure

RDS: Redundant Data Sets

RA: Redundant Algorithms

AC: Algorithmic Complexity

VSA: Version Sequential Arrangement

TC: Timing Constraints

NCP

High

N / A

Average

N / A

N / A

slide23

Retry Block - Data Diversity

CIS: Control Implementation Structure

RDS: Redundant Data Sets

RA: Redundant Algorithms

AC: Algorithmic Complexity

VSA: Version Sequential Arrangement

TC: Timing Constraints

Retry Block

High

N / A

Average

N / A

High

slide26

Function Point Calculations ….

Definition of numerical assignment rules

CIS = RDS + RA + AC + VSA + TC

1.The lowest CIS * Percentage > 1 in both category.

2.The lowest CIS * Percentage (Design Diversity) > the highest CIS * Percentage (Data Diversity)

CIS Factor = (RDS + RA + AC + VSA + TC) * Diversity Percentage

30% for Diversity Percentage in Design Diversity Category

22% for Diversity Percentage in Data Diversity Category

EFP = Management FP + Control FP * CIS Factor

slide30

Representation of Requirements

Functional users requirements

Software

Functional processes

Sub-process

Data

transform type

Data

movement type

and

slide31

Factors for Extended Metrics Framework

  • Structural complexity
  • Functional size
  • Fault tolerant requirements
  • Algorithm complexity
  • Algorithm implementation
  • Reused-algorithms
  • Connectivity
  • Effort
slide32

Summary and Future Work

  • By augmenting new elements based on FFP and

FPA techniques, a new Extensive Function Point

composite metrics has been proposed for

software with real-time and fault-tolerant

attributes.

  • Future work will focus on data collection and

validation of the proposed metrics framework.