Page 234 - Software and Systems Requirements Engineering in Practice

ç ç 3 O F T W A R E ç ç 3 Y S T E M S ç 2 E Q U I R E M E N T S ç % N G I N E E R I N G ç ) N ç 0 R A C T I C E

7HY $ECISIONS 3HOULD "E $OCUMENTED
/N A LARGE NUCLEAR POWER PLANT PROJECT IN THE EARLY S A
MULTIPROCESSING SUPERCOMPUTER HAD BEEN PURCHASED "ECAUSE OF FEATURE
CREEP THE COMPUTING CAPACITY HAD BEEN EXCEEDED AND AN ADDITIONAL
PROCESSOR HAD TO BE ADDED AT A COST OF SEVERAL HUNDRED THOUSAND DOLLARS
4HE CLIENT AGREED TO PAY FOR THE CHANGE THE AGREEMENT WAS DOCUMENTED
IN THE PROJECT MEETING MINUTES A CHANGE REQUEST WAS ISSUED TO PURCHASE
AND INSTALL THE ADDITIONAL PROCESSOR AND THE PROJECT PROCEEDED ! YEAR
LATER THE CLIENT REFUSED TO PAY FOR THE PROCESSOR CLAIMING THAT THE
SUPPLIER HAD AGREED TO PAY FOR IT 4HE PROJECT MANAGER HAD NOT RETAINED
COPIES OF THE MEETING MINUTES AND AS A RESULT COULD NOT FIND A WRITTEN
RECORD OF THE AGREEMENT *UST BEFORE THE ISSUE WENT TO LITIGATION A COPY
OF THE AGREEMENT WAS FOUND IN A SET OF FILES THAT WERE ABOUT TO BE THROWN
OUT AND THE CLIENT AGREED TO PAY THE FULL COST OF THE UPGRADE

CASH FLOW PREEMPT COMPETITION ETC )F REQUIREMENT DEPENDENCIES
AND TRACES ARE NOT MAINTAINED PLANNING CAN BE DIFFICULT $ERIVATION
ANALYSIS MAY BE NEEDED TO DETERMINE THE POTENTIAL RETURN ON
INVESTMENT FOR A FEATURE AND THAT IN TURN REQUIRES A STABLE IN PLACE
TRACING STRATEGY SEE THE NEXT SECTION

4RACEABILITY
h2EQUIREMENTS TRACEABILITY IS THE ABILITY TO DESCRIBE AND FOLLOW THE
LIFE OF A REQUIREMENT IN BOTH A FORWARD AND BACKWARD DIRECTION I E
FROM ITS ORIGINS THROUGH ITS DEVELOPMENT AND SPECIFICATION TO ITS
SUBSEQUENT DEPLOYMENT AND USE AND THROUGH PERIODS OF ONGOING
REFINEMENT AND ITERATION IN ANY OF THESE PHASESv ;'OTEL ET AL =
7E DISCUSS TRACEABILITY IN SOME DETAIL HERE AS IT CAN BE A DIFFICULT
DAUNTING TASK AND IT MAY BE VITAL TO THE SUCCESS OF A PROJECT
4RACEABILITY IS THE KEY TO COVERAGE DERIVATION AND IMPACT ANALYSES
! REQUIREMENT IS TRACEABLE IF AND ONLY IF THE ORIGIN OF EACH OF ITS
COMPONENT REQUIREMENTS IS CLEAR AND IF THERE IS A MECHANISM THAT MAKES
IT FEASIBLE TO REFER TO THAT REQUIREMENT IN FUTURE DEVELOPMENT EFFORTS
;)%%% =
! SUGGESTED APPROACH TO DEFINING A TRACEABILITY STRATEGY IS TO LOOK
AT THE ROLES ON THE PROJECT AND THEIR NEEDS IMPLEMENTING TRACING
MECHANISMS ONLY WHERE NECESSARY 3EVERAL DIFFERENT CATEGORIES OF
STAKEHOLDERS ARE LISTED IN 4ABLE ALONG WITH THEIR TRACING NEEDS
"ECAUSE THE ACTUAL NEEDS DIFFER DEPENDING ON THE KIND OF ORGANIZATION
TRACING NEEDS ARE DEFINED BY ORGANIZATION AND BY ROLE
$IFFERENT PROJECTS WILL HAVE DIFFERENT TRACE MECHANISMS FOR DIFFERENT
REASONS ! PURCHASER OF A PRODUCT OR SERVICES REFERRED TO AS THE BUYER
WILL NEED TRACES THAT ARE DIFFERENT FROM THOSE OF THE VENDOR PROVIDING
THE SERVICES REFERRED TO AS THE CONTRACTOR 4HESE TWO SETS OF TRACES WILL
IN TURN BE DIFFERENT FROM THE KINDS OF TRACES USED BY A DEVELOPMENT