9. requirements management

5/24/2018 9. Requirements Management

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RequirementsManagement

S u m m a r y Requirements management is concerned with all of theprocesses involved in changing system requirements. In thischapter, we suggest guidelines which relate directly to theprocesses which are part of requirements management andwhich provide some practical information on techniques usedfor requirements management. The guidelines that we suggesta r e :

G u i d e l i n e s9 1 Uniquely Identi fy Each Requirement9 29 39 49 59 69 79 89 9

De fine Pol ic ies for Requirements Managem entDefine Traceability PoliciesM ainta in a Traceabil ity M anualUse a Database to M an age RequirementsDe fine C hange Managem ent Polic iesIdenti fy G lobal System RequirementsIdenti fy V olat i le RequirementsRecord Re jected Requ irem ents


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216 Requirements M anage m entDuring the processes of requirements engineering, systemdevelopment and operation, new requirements emergeand existing requirements change. These changingrequirements must be managed to ensure that the qualityof the requirements is maintained. The impact of require-ments changes must be understood and requirementschanges implemented in a timely and cost-effective way.It is also important to ensure that the requirements keepin step with the operational system. System changes mustbe reflected as requirements changes and vice-versa.Requirements management is, therefore, a processwhich supports other requirements engineering activitiesand is carried out in parallel with them. A recentEuropean survey of 4000 companies found that themanagement of customer requirements was one of theprincipal problem areas in software development andproduction. These problems were not confined to themanagement of requirements for external clients. Therewere also problems of managing requirements changewhere the system was being specified and developed inthe same organisation.

Problems with requirements management often meanthat systems whose requirements do not satisfy the custo-mer are delivered. Systems development schedules maybe extended and high costs incurred for rework of thedesign and implementation to accommodate requirementschanges. The costs of these problems in the long-termusually outweigh the short-term costs of introducing goodrequirements management practice.The principal concerns of requirements managementa r e :

1 managing changes to agreed requirements2 managing the relationships between requirements3 managing dependencies between the requirements docu-ment and other documents produced during the systemsand software engineering process.

Requirements changes may be due to errors and misun-derstandings in the requirements engineering process,design or implementation problems. New requirementsmay emerge as stakeholders develop a deeper understand-


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Requirements Man agem ent 217i ng o f t h e s y s te m . M o s t c o m m o n l y , h o w e v e r , r e q u i re -m e n t s c h a n g e i s a r e s u l t o f c h a n g i n g e x t e r n a l c i r c u m -s t a n c e s. T h e s t ra t e g y o r p r i o r it i e s o f t h e b u s i n e s s b u y i n gt h e s y s t e m m a y c h a n g e a s a r e s u l t o f c h a n g i n g e c o n o m i cc i r c u m s t a n c e s o r n e w c o m p e t i to r s i n its m a r k e t. N e wi n fo r m a t i o n a b o u t th e s y s t e m ' s e n v i r o n m e n t m a y b e c o m ea va i l a b l e , e . g . ne w d i g i t a l ma ps fo r a ge ogr a ph i c i n fo r ma -t i o n s y s t e m . N e w l a w s o r r e g u l a t i o n s m a y b e i n t r o d u c e dw h i c h r e q u i r e s y s t e m c h a n g e .T o m a n a g e r e q u i r e m e n t s , y o u n e e d t o m a i n t a i n r e q u i r e -m e n t s t r a cea b i l i t y i n f o r m a t i o n . A r e q u i r e m e n t i s t r a c e a b l ei f y o u c a n d i s c o v e r w h o s u g g e s te d t h e re q u i r e m e n t , w h yt h e r e q u i r e m e n t e x i s t s , w h a t r e q u i r e m e n t s a r e r e l a t e d t o i ta n d h o w t h a t r e q u i r e m e n t r e l a t e s t o o t h e r i n f o r m a t i o ns u c h a s s y s t e m s d e s i g n s , i m p l e m e n t a t i o n s a n d u s e r d o c u -m e n t a t i o n . T r a c e a b i l i t y i n f o r m a t i o n h e l p s y o u d i s c o v e rw h a t o t h e r r e q u i r e m e n t s m i g h t b e a f f e c t e d b y r e q u i r e -m e n t s c h a n g e s .G o o d r e q u i r e m e n t s m a n a g e m e n t p r a c t i c e s s u c h a s m a i n -t a i n i n g d e p e n d e n c i e s b e t w e e n r e q u i r e m e n t s h a v e l o n g -t e r m b e n e f i t s . T h e s e a r e b e t t e r c u s t o m e r s a t i s f a c t i o n a n dl o w e r s y s t e m d e v e l o p m e n t c o s t s . T h e s e r e t u r n s a r e n o ti m m e d i a t e s o r e q u i r e m e n t s m a n a g e m e n t m a y a p p e a r t od e v e l o p e r s a s a n o v e r h e a d . I t m a k e s i t m o r e d i f fi c u lt f ort h e m t o m a k e c h a n g e s t o t h e s y s t e m o n t i m e a n d w i t h i nb u d g e t . I n t h e s e c i r c u m s t a n c e s , y o u m u s t p e r s e v e r e ;e x p e r i e n c e h a s s h o w n t h a t i n v e s t m e n t i n g o o d r e q u i r e -m e n t s m a n a g e m e n t p r o c e s s e s i s a l w a y s c o s t - e f f e c t i v e .


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218 Requirements Management

Key benefitCosts of introductionCosts o f applicationGuidel ine type

Unambiguous references tospecific requirements arepossibleVery lowVery lowBasic

Each requirement should be assigned a unique identifieror reference number which may be used to refer to thatrequirement in other parts of the requirements documentor in other system documentation.Benefits

Unique identifiers may be used to make references torelated requirements and to construct t r a c e a b i l i t y t a b l e s(see Guideline 9.3).

If you store your requirements in a database (see G u i d el ine 9.5), the requirement identifier may serve as aprimary key which uniquely identifies the requirement inthe database. References from one requirement to anotherin the database may use this primary key.

Requirements inevitably evolve and you may wish tomanage this evolution by using a configuration manage-ment system. The requirement reference number can bethe basis for linking versions of the requirements whichhave evolved from the same starting point.

Implementat ionThe most commonly used approach to requirements iden-tification is to assign numbers depending on the chapterand section of the requirements document where therequirement is included. Therefore, the 6th requirementin the 2nd section in chapter 4 would be 4.2.6.


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Un iquely Identify Each Requ irement 2 1 9T h e r e a r e tw o d i f f ic u l t i e s w i t h t h i s s t y l e of r e q u i r e -m e n t s i d e n t i f i c a t i o n . F i r s t l y , w h e n y o u c o l l e c t a r e q u i r e -m e n t , y o u d o n o t k n o w w h e r e i t w i l l a p p e a r i n t h e

d o c u m e n t s o y o u c a n n o t a s s i g n i t a n u m b e r u n t i l av e r s i o n o f t h e r e q u i r e m e n t s d o c u m e n t is i s s u e d . T h i sm e a n s t h a t i t i s d i f f i c u l t t o r e f e r t o i t i n o t h e r r e q u i r e -m e n t s . S e c o n d l y , a s s i g n i n g a n i d e n t i f i e r b a s e d o n c h a p t e ra n d s e c t i o n n u m b e r s p o s i t i o n s t h e r e q u i r e m e n t i n a c l a s -s i f i c a t i o n s t r u c t u r e . I t s u g g e s t s t h a t t h e r e q u i r e m e n t i sm o s t c lo s e l y r e l a t e d to o t h e r r e q u i r e m e n t s w i t h s i m i l a ri d e n t if i e rs . D o c u m e n t r e a d e r s m a y be m i s l e d i n t o t h i n k i n gt h a t t h e r e a r e n o o t h e r i m p o r t a n t r e l a t i o n s h i p s b e t w e e nt h a t r e q u i r e m e n t a n d o t h e r r e q u i r e m e n t s e l s e w h e r e i n t h ed o c u m e n t .Y o u c a n a d d r e s s t h i s p r o b l e m i n t w o w a y s .

S o m e w o r d - p r o c e s s i n g s y s t e m s a l l o w f o r a u t o m a t i cr e n u m b e r i n g o f p a r a g r a p h s a n d t h e i n c l u s i o n o f c r os s-r e f e r e n c e s . Y o u c a n t h e r e f o r e a s s i g n a n u m b e r t o ar e q u i r e m e n t a t a n y t i m e . A s y o u r e - o r g a n i s e y o u r d o c u -m e n t a n d a d d n e w r e q u i r e m e n t s , t h e s y s t e m k e e p s t r ac ko f t h e c r o s s- r e fe r e n c e a n d a u t o m a t i c a l l y r e n u m b e r s y o u rr e q u i r e m e n t d e p e n d i n g o n i t s c h a p t e r , s e c t i o n a n d p o s i -t i o n w i t h i n t h e s e c t i o n . T h i s i s t h e s o l u t i o n w e r e c o m -m e n d i f y o u h a v e t h e r ig h t k i n d o f w o r d p r o c e s s o rf ac i l i t i e s .

Y o u c a n a s s i g n a n i n t e r i m i d e n t i fi e r t o e a c h r e q u i r e m e n tt h e n r e p la c e i t w i t h s o m e n u m b e r w h e n y o u p r o d u c ey o u r f i n a l d o c u m e n t . R a t h e r t h a n a n u m b e r , y o u a r e b e s tto u se s o m e m n e m o n i c d e r i v e d f r o m t h e c o n t e n t s o f t h er e q u i r e m e n t e .g . E F F - 1, E F F - 2, E F F- 3 f or r e q u i r e m e n t sw h i c h c o n c e r n t h e e f f ic i e n c y of t h e s y s t e m .T h e s e s c h e m e s a p p l y to r e q u i r e m e n t s e x p r e s s e d a s t e xt .S y s t e m m o d e l s ( s e e C h a p t e r 7 ) s h o u l d a l s o b e a s s i g n e d au n i q u e i d e n ti f ie r . P a r t s o f a s y s t e m m o d e l s u c h a s e n ti t ie si n a d i a g r a m d o n o t n e e d t o h a v e a g l o b a l l y u n i q u e i d e n t i -f ie r b u t t h e i r n a m e s s h o u l d b e u n i q u e w i t h i n t h e m o d e l .T h e y m a y b e r e f e r e n c e d b y g iv i n g t h e m o d e l i d e n t i f ie rt h e n t h e e n t i t y n a m e .


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220 Requirements ManagementCosts and problems

I n t r o d u c i n g a n d i m p l e m e n t i n g t h i s g u i d e l i n e i s v e r ych eap . T o in t r o d u ce i t , t h e o n ly co s t s a r e t h e co s t s o fd e f i n i n g a n u m b e r i n g c o n v e n t i o n . P e o p l e s o m e t i m e s l i k et o a r g u e o v e r n u m b e r i n g s c h e m e s b u t r e a c h i n g a g r e e m e n to n a n u m b e r i n g s c h e m e s h o u l d n o t b e a s i g n i f i c a n tp r o b l e m i n m o s t o r g a n i s a t i o n s . T h e c o s t s o f a p p l y i n g t h eg u i d e l i n e a r e th e c o s ts o f r e n u m b e r i n g r e q u i r e m e n t s w h e nc h a n g e s a r e m a d e . T h e s e a r e n e g l ig i b le i f s o m e a u t o m a t i cr e n u m b e r i n g s y s t e m i s a v a i l a b l e .


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D efine Pol ic ies for Req uirem ents M anagem ent 221

Key bene fit Prov ide guid anc e for allinvolved in requirementsmanagementCosts of introduction ModerateCosts of applicat ion LowGuidel ine type Basic

R e q u i r e m e n t s m a n a g e m e n t p o l i c i e s d e f i n e g o a l s f o rr e q u i r e m e n t s m a n a g e m e n t , t h e p r o c e d u r e s w h i c h s h o u l db e f o l l o w e d a n d t h e s t a n d a r d s w h i c h s h o u l d b e u s e d .T h e s e p o l i c i e s s h o u l d b e e x p l i c i t l y d e f i n e d a s p a r t o fy o u r q u a l i t y m a n a g e m e n t s y s t e m .

Benefits E x p l i c i t p o l i c ie s te l l p e o p l e i n v o l v e d i n t h e p r o c e s s w h a tt h e y a r e e x p e c t e d t o d o a n d w h y i t s h o u l d b e d o n e .P r o j e c t s g e n e r a l l y m a n a g e t h e i r r e q u i r e m e n t s i n c o m p a r -ab l e w ay s s o , w i th ex p l i c i t p o l i c i e s , t h e r e i s l e s s d ep en -d e n c e o n i n d i v i d u a l k n o w l e d g e a n d e x p e r t i s e . I n o r d e r t o d e f i n e p o l ic i e s , y o u m u s t u n d e r s t a n d y o u re x i s ti n g p r o c e s s e s f o r r e q u i r e m e n t s m a n a g e m e n t . T h i s isl i k e l y t o r e v e a l p r o b l e m a r e a s w h i c h m a y b e c o m e t h ef o cu s o f p r o c e s s i m p r o v e m e n t s .

Implementa t ionR e q u i r e m e n t s m a n a g e m e n t p o l i c ie s a r e a b a s i s fo r t h eq u a l i t y m a n a g e m e n t o f t h e s y s t e m r e q u i r e m e n t s . P o l i c ie sa r e n o t t h e s ame as s t an d a r d s b u t a r e c l ea r ly r e l a t ed toth em. Po l i c i e s , l o o s e ly , s e t o u t w h a t s h o u l d b e d o n e ; s t a n -d a r d s d e s c r i b e h o w t h e p o l i c y s h o u l d b e i m p l e m e n t e d i na p a r t i c u l a r s i t u a t i o n . S o m e p o l i c i e s m a y b e r e f l e c t e d i no r g a n i s a t i o n a l s t a n d a r d s b u t i n d i v i d u a l p r o j e c t m a n a g e r s


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222 Requireme nts M ana gem enta r e s o m e t i m e s t h e b e s t j u d g e o f h o w p o l i c ie s s h o u l d b ei m p l e m e n t e d .O r g a n i s a t i o n s s h o u l d d e f i n e a g e n e r a l s e t o f r e q u i re -m e n t s m a n a g e m e n t p o l i c i e s . F o r e a c h p r o j e c t , y o u m u s tl o o k a t t h i s g e n e r a l s e t o f p o l i c ie s a n d s e l e c t t h o s e w h i c ha r e r e l e v a n t t o t h a t p r o j e c t . T h e y m a y b e a m e n d e d i ns o m e w a y s to s u i t t h e s p e c i f i c n eed s o f t h e p r o j ec t .G e n e r a l r e q u i r e m e n t s m a n a g e m e n t p o l i c i e s s h o u l di n c l u d e :

1 a s e t o f o b je c t iv e s fo r t h e r e q u i r e m e n t s m a n a g e m e n t p r o -c e s s a n d r a t i o n a l e a s s o c i a t e d w i t h e a c h o f t h e s e o b je c t iv e s2 t h e r e p o r ts w h i c h s h o u l d b e p r o d u c e d t o m a k e th er e q u i r e m e n t s e n g i n e e r i n g p r o c e s s v i s i b l e a n d t h e a c t i v -i t i e s w h i c h a r e e x p e c t e d t o p r o d u c e t h e s e r e p o r t s a s d e l i -v e r a b l e s3 t h e s t a n d a r d s f or r e q u i r e m e n t s d o c u m e n t s a n d r e q ui re -m e n t s d e s c r i p t i o n s w h i c h s h o u l d b e u s e d ( s e e Gu i d e l i n e3.1, D e f i n e a s t a n d a r d d o c u m e n t s t r u c t u r e and 6 .1 , D e f i n es ta n d a r d t e m p l a t e s fo r d e sc r i b i n g r e q u i r e m e n t s4 c h a n g e m a n a g e m e n t a n d c o n tr o l p o l ic i e s fo r r e q u i r e m e n t s( s ee G u id e l in e 9 .6 )5 r e q u i r e m e n t s r e v i e w a n d v a l i d a t io n p o l ic i e s6 r e l a t i o n s h i p s b e t w e e n r e q u i r e m e n t s m a n a g e m e n t a n do t h e r s y s t e m e n g i n e e r i n g a n d p r o j e c t p l a n n i n g a c t i v i t i e s7 t r a c e a b i l i t y p o l i c i e s w h i c h d e f i n e w h a t i n f o r m a t i o n o n

d e p e n d e n c i e s b e t w e e n r e q u i r e m e n t s s h o u l d b e m a i n -t a i n e d a n d h o w t h i s i n f o r m a t i o n s h o u l d b e u s e d a n dm a n a g e d ( s e e G u i d e l i n e 9 . 3 )8 c r i te r i a w h e n t h e s e p o l i c i e s c a n b e ig n o r e d ; in th e s es i t u a t i o n s , m a n a g e r s u s e t h e i r o w n j u d g e m e n t o n h o w t oi m p l e m e n t a r e q u i r e m e n t s c h a n g e .

O f co u r s e , i t i s u n r ea l i s t i c t o ex p ec t t o d e f in e an d in t r o -d u c e a l l o f t h e s e p o l i c i e s a t t h e s a m e t im e . T h e y s h o u l db e d e v e l o p e d i n c r e m e n t a l l y a n d u p d a t e d a f t e r y o u h a v ep r a c t ic a l e x p e r i e n c e o f t h e i r a p p l i c a t i o n i n r e q u i r e m e n t sm a n a g e m e n t .Y o u m u s t b u i l d s o m e f l e x i b i l i t y i n t o y o u r p o l i c i e s


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De fine Pol ic ies for Requirem ents M anag em ent 223o t h e r w i s e t h e y w i l l b e u n w o r k a b l e . T h e r e i s s o m e t i m e ss u c h a n u r g e n t n e e d f o r s y s t e m c h a n g e , t h a t i t i s i m p o s s i -b l e t o f o l l o w t h r o u g h a s y s t e m a t i c r e q u i r e m e n t s m a n a g e -m e n t p o l i c y b e f o r e i m p l e m e n t i n g t h a t c h a n g e . Y o u m u s th a v e s o m e m e c h a n i s m fo r m a n a g i n g t h e s e e x c e p t i o n s . Its h o u l d s u g g e s t h o w y o u m a i n t a i n t h e i n f o r m a t i o n w h i c hc a n e v e n t u a l l y b e u s e d t o u p d a t e t h e r e q u i r e m e n t s w h i c ha r e b e i n g m a n a g e d .

Costs and problemsI t m ay t ak e s ev e r a l m o n th s o f e f fo r t an d a t l ea s t a y ea r o fc a l e n d a r t i m e t o e s ta b l i s h a c o h e r e n t s e t o f r e q u i r e m e n t sm a n a g e m e n t p o l i c i e s . Y o u m u s t c o n s u l t w i t h t h o s ei n v o l v e d i n t h e r e q u i r e m e n t s e n g i n e e r i n g p r o c e s s ,p r o p o s e , r e v i e w a n d a m e n d p o l i c i e s t h e n i n t r o d u c e ad i s s e m i n a t i o n a n d t r a i n i n g p r o g r a m m e t o e n s u r e t h a tp e o p l e a r e a w a r e o f t h e p o l ic i e s a n d k n o w h o w t o a p p l yt h e m .W h e n p o l i c i e s h a v e b e e n d e f i n e d , y o u m u s t c h e c k t h a tt h e p r o c e d u r e s a n d s t a n d a r d s i m p l e m e n t i n g t h e s e p o l i c i e sa r e b e i n g f o l l o w e d . T h e c o s t s o f a p p l y i n g t h i s g u i d e l i n ea r e t h e r e f o r e p a r t o f y o u r q u a l i t y a s s u r a n ce co s ts .I n p r i n c i p l e , p e o p l e w i l l a l w a y s b e s u p p o r t i v e o fr e q u i r e m e n t s m a n a g e m e n t p o l i c i e s . I n p r a c t i c e , h o w e v e r ,y o u m a y f i n d t h a t t h e y d o n o t g iv e t h e c r e a t i o n o f t h e s ep o l i c i e s a h ig h p r io r i t y . T h i s i s p a r t i cu l a r ly l i k e ly f o rt h o s e w h o a r e n o t d i r e c t l y i n v o l v e d i n r e q u i r e m e n t s e n g i -n ee r in g . T h ey may f ee l t h a t t h i s i s n o t t h e i r r e s p o n s ib i l i t y .H o w e v e r , y o u m u s t t r y to i n v o l v e t h e s e p e o p l e . I f y o u d on o t , th e y w i ll , a t b e s t, c o m p l a i n t h a t t h e y w e r e n o tco n s u l t ed ; a t w o r s t , t h ey w i l l r e f u s e t o accep t t h e p o l i c i e sw h i c h h a v e b e e n p r o p o s e d .


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224 Requirements Managem ent

Key ben efit Leads to con sistent tracea bilityinformation being m aintainedfor all systemsCosts of introduct ion ModerateCosts of appl icat ion Modera te-h ighGu i d e l i n e type Basic- intermediate

A s p a r t of y o u r r e q u i r e m e n t s m a n a g e m e n t p o li c y, y o us h o u l d d e f i n e w h a t t r a c e a b i l i t y i n f o r m a t i o n s h o u l d b em a i n t a i n e d a n d h o w t h i s s h o u l d b e r e p r e s e n t e d . T r a c e -a b i l i t y i n f o r m a t i o n i s i n f o r m a t i o n w h i c h a l l o w s y o u t of i n d d e p e n d e n c i e s b e t w e e n r e q u i r e m e n t s , a n d b e t w e e nt h e r e q u i r e m e n t s a n d t h e s y s t e m d e s i g n , c o m p o n e n t s a n dd o c u m e n t a t i o n .Benefits T r a c e a b i l i ty i n f o r m a t i o n is s t a n d a r d i s e d . T h o s e r e s p o n s i -b l e f o r a s s e s s i n g r e q u i r e m e n t s c h a n g e s t h e r e f o r e k n o ww h a t i n f o r m a t i o n i s l i k e l y t o b e a v a i l a b l e a n d h o w i t w i l lb e r e p r e s e n t e d .

T r ac eab i l i t y p o l i c i e s a r e a b as i s fo r co s t an d q u a l i t yc o n t r o l . C o l l e c t i n g a n d m a n a g i n g t r a c e a b i l i t y i n f o r m a t i o ni s e x p e n s i v e . T r a c e a b i l i t y p o l i c i e s m e a n t h a t y o u c a nco n t r o l t h es e co s t s b y co l l ec t in g e s s en t i a l t r aceab i l i t yi n f o r m a t i o n a n d n o t c o l l e c t in g l a rg e a m o u n t s o f i n fo r m a -t i o n w h i c h y o u c a n n o t m a i n t a i n . I t m ay b e p o s s ib l e to p r o v id e s o m e s o ftw ar e s u p p o r t fo ry o u r d e f in ed p o l i c i e s .

Implementa t ionT r a c e a b i l i t y p o l i c i e s a r e w r i t t e n p o l i c i e s w h i c h s h o u l dd e f in e th e f o l lo w in g .

T h e t r a c e a b i l it y i n f o r m a t i o n w h i c h s h o u l d b e m a i n t a i n e d .T h i s i s d e s c r i b e d i n m o r e d e t a i l b e l o w .


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Define Traceabil ity Policies 225 T h e te c h n i q u e s w h i c h m a y b e u s e d f or m a i n t a i n i n g t ra c e -ab i l i ty . This i s descr ibed in more de ta i l be low. A d e s c r i p ti o n o f w h e n t h e t r a c e a b il it y i n f o r m a t i o n s h o u l db e c o l l e c t e d d u r i n g t h e r e q u i r e m e n t s e n g i n e e r i n g a n ds y s t e m d e v e l o p m e n t p r o c e s s e s . Y o u s h o u l d a l s o d e f i n et he r o l e s o f t he p eop l e , s uch a s t he t r acea b i l it y m anage r ,who a r e r e s pons i b l e fo r m a i n t a i n i ng t he t r aceab i l i t y i n fo r -m a t i on . A d e s c r i p ti o n o f h o w to h a n d l e a n d d o c u m e n t p o l ic yexcep t i ons , t ha t i s , when t i m e cons t r a i n t s m ake i t i m pos -s i b l e t o i m p l em en t t he no r m al t r aceab i l i t y po l i cy . Rea l i s t i -

ca l l y , t he r e w i l l a l ways be occas i ons wher e you have t om a k e c h a n g e s t o t h e r e q u i r e m e n t s o r t h e s y s t e m w i t h o u tf i r s t a s s es s i ng a l l change i m pac t s and m a i n t a i n i ng t r ace -ab i l i t y i n fo r m a t i on . T he po l i cy excep t i ons s hou l d de f i neh o w t h e s e c h a n g e s s h o u l d b e s a n c t i o n e d . T h e t r a c e a b i l i t ypo l i c i e s s hou l d a l s o de f i ne t he p r oces s u s ed t o ens u r et h a t t h e t r a c e a b i l i t y i n f o r m a t i o n i s u p d a t e d a f t e r t h ec h a n g e h a s b e e n m a d e .T r aceab i l i t y po l i c i e s s hou l d be wr i t t en s o t ha t t hey a r ei n d e p e n d e n t o f a n y p a r t i c u l a r s y s te m . A s p a r t o f y o u rqua l i t y p l ann i ng p r oces s , you s hou l d s e l ec t t he m os t r e l e -van t t r aceab i l i t y po l i c i e s and t a i l o r t hem t o t he s pec i f i cnee ds o f t he s ys t em w h i c h i s be i ng s pec i f ied . T h es es h o u l d t h e n b e d e f i n e d i n t h e s y s t e m t r a c e a b i l i t y m a n u a l(see Guidel ine 9 .4} .M a i n t a i n i n g t r a c e a b i l i t y i n f o r m a t i o n i s e x p e n s i v ebec aus e i t i nvo l ves m ana g i ng l a rge vo l um e s o f i n fo rm a -t i o n . R e q u i r e m e n t s c h a n g e s m a y i n v o l v e m a k i n g c h a n g e st o t h i s t r aceab i l i t y i n fo r m a t i on i n s eve r a l p l aces t o r eco r dn e w o r c h a n g e d d e p e n d e n c i e s . Y o u m u s t b e r e a l i s t i c i nd e f i n i n g y o u r t r a c e a b i l i t y p o l i c i e s a n d y o u s h o u l d n o tm ake t hem t oo bu r eauc r a t i c . I t i s be t t e r t o have l i gh t -w e i g h t p o li c ie s w h i c h a r e f o ll o w e d r a t h e r t h a n m o r ec o m p r e h e n s i v e t r a c e a b i l i t y p o l i c i e s w h i c h a r e i g n o r e d b yp r o j ec t m anage r s .T h i s g u i d e l i n e m a y b e i m p l e m e n t e d b y o r g a n i s a t i o n s a ta n y l e ve l o f r e q u i r e m e n t s e n g i n e e r i n g p r o c e s s m a t u r it y .S i m p l e t r a c e a b i l it y o f r e q u i r e m e n t s to t h e i r s o u r c e s a n do t h e r r e q u i r e m e n t s m a y b e i m p l e m e n t e d b y o r g a n i s a t i o n s


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2 2 6 Requirements Managementat the basic level in the requirements engineering processmaturity model. As organisational maturity increases,more complex traceability policies maybe introduced.

Traceability informationThere are different types of traceability information whichyou might want to maintain. These are shown in Figure9.1.There are three basic techniques which may be used tomaintain traceability information. These are as follows.

1 T r a c e a b i l i t y t a b l e s . A cross-reference matrix is producedwhere the entries in the table indicate some kind of trace-

Traceability t y p e DescriptionR e q u i r e m e n t s - s o u r c e s t r a c e a b i l i t y L i n k s t h e r e q u i r e m e n t a n d t h e p e o p l e o r d o c u m e n t swhic h spec i f i ed the r equ i r ement . See Guide l ine 4 . 4 ,Record requirements sourcesRequi r ement s - r a t iona l e t r ac eab i l i t y L in k s t h e r e q u i r e m e n t w i t h a d e s c r i p t io n o f w h ytha t r equ i r ement has been spec i f i ed . See Guideline4.7, Record requirements rationaleR e q u i r e m e n t s - r e q u i r e m e n t st raceabi l i ty L i n k s r e q u i r e m e n t s w i t h o t h e r r e q u i r e m e n t s w h i c ha re , i n some way , dependen t on them. You shou lda lways t ry to ma in t a in th i s t ype o f i n f o rma t ion .Requi r ement s - a rc h i t ec tu ret raceabi l i ty Links r equ i r ement s w i th the sub- sys t ems whe rethese r equ i r ement s a r e implemented . T h i s i s

pa r t i c u l a r ly impor t an t whe re sub- sys t ems a r e be ingdeve loped by d i f fe r en t sub- c on t rac to r s .Requi r ement s - des ign t r ac eab i l i t y Links r equ i r ement s w i th spec i f i c c omponen t s i n t hes y s t e m w h i c h a r e u s e d t o i m p l e m e n t t h erequ i r ement . T hese may be ha rdware o r so f twarec omponen t s . I t i s pa r t i c u l a r ly impor t an t t o ma in t a inthis typ e of inform at ion for c r i t ica l sys tem s.Requ i r ement s - in te r f ac e t r ac eab i l it y Links r equ i r ement s w i th the in t e r f ac es o f ex t e rna lsys t ems w hic h a r e used in the p rov i s ion o f t her e q u i re m e n t s . S h o u l d b e m a i n t a i n e d w h e r e t h e r e is ah i g h d e p e n d e n c y o n o t h e r s y s t e m s .

Figure 9 .1 T y p e s o f t r a c e a b i l i t y i n f o r m a t i o n


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Define Traceabi l i ty Pol icies 227a b i li ty l i n k b e t w e e n t h e i t e m s i n th e r o w s a n d t h e i t e m si n t h e c o l u m n s .

2 T r a c e a b i l i t y l i st s. E a c h r e q u i r e m e n t h a s a li s t o f a s s o-c i a t e d t r a c e a b i l i t y i n f o r m a t i o nA u t o m a t e d t r a c e a b i l i t y l i nk s. T h e r e q u i r e m e n t s a r e m a i n -t a i n e d i n a d a t a b a s e a n d t r a c e a b i l i t y l i n k s a r e i n c l u d e d a sf i e l d s i n t h e d a t a b a s e r e c o r d . T h i s i s c o v e r e d i n G u i d e l i n e9 5

T r a c e a b i l i t y t a b l e sT r a c e a b i l i t y t a b l e s s h o w t h e r e l a t i o n s h i p s b e t w e e nr e q u i r e m e n t s o r b e t w e e n r e q u i r e m e n t s a n d d e s i g n c o m p o -n e n t s . T h e r e q u i r e m e n t s a r e l i s t e d a l o n g t h e h o r i z o n t a la n d v e r t i c a l a x e s a n d r e l a t i o n s h i p s b e t w e e n r e q u i r e m e n t sa r e m a r k e d i n t h e t a b l e c e l l s . T h e y c a n b e i m p l e m e n t e du s i n g w o r d p r o c e s s o r o r s p r e a d s h e e t t a b l e s ; a r e q u i r e -m e n t s d a t a b a s e i s n o t n e c e s s a r y .

T r a c e a b il i t y ta b le s f or s h o w i n g r e q u i r e m e n t s d e p e n d e n -c i e s s h o u l d b e d e f i n e d w i t h r e q u i r e m e n t n u m b e r s u s e d t ol a b el th e r o w s a n d c o l u m n s o f t h e t ab le . I n t h e s i m p l e s tf o r m o f t r a c e a b i li t y ta b le , y o u s i m p l y p u t s o m e m a r k s u c ha s a * i n t h e t a b l e c e ll w h e r e t h e r e i s s o m e k i n d o f d e p e n -d e n c y r e l a t i o n s h i p b e t w e e n t h e r e q u i r e m e n t s i n t h e c e l lr o w a n d c o l u m n . T h a t i s, i f t h e r e q u i r e m e n t i n r o w X

R1R2R3R4R5R6

R1 R2Depends onR3 R4 R5 R6

Figu re 9,2 A s im ple tracea bil i ty table


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228 Requirements M anagem ent( s a y ) d e p e n d s o n t h e r e q u i r e m e n t i n c o l u m n s P , Q , a n dR, you should mark table cel ls (X, P) , (X, Q) , and (X, R) .B y r e a d i n g d o w n a c o lu m n , y o u s ee a ll r e q u i r e m e n t sw h i c h d e p e n d o n a r e q u i r e m e n t ; b y r e a d i n g a c r o s s a r o w ,y o u s e e a l l r e q u i r e m e n t s w h i c h t h e r e q u i r e m e n t i n t h a tr o w d e p e n d s o n .A v e r y s i m p l e e x a m p l e o f a t r a c e a b i l it y ta b l e is s h o w nin F ig u r e 9 .2 f o r a s y s t em w i th s ix r eq u i r emen t s .E a c h r o w i n t h e t a b l e s h o w s d e p e n d e n c i e s s o t h a t R 1 i sd e p e n d e n t o n R 3 a n d R 4 , R 2 i s d e p e n d e n t o n R 5 a n d R 6 ,e tc . T h e r e f o r e , i f a ch an g e to R4 is p r o p o s e d , w e c an s eeb y r e a d i n g d o w n t h e R 4 c o l u m n t h a t r e q u i r e m e n t s R 1 a n dR 3 a r e d e p e n d e n t r e q u i r e m e n t s . Y o u s h o u l d t h e r e f o r ea s s e s s t h e i m p a c t o n R1 a n d R 3 o f t h e p r o p o s e d c h a n g eto R4.Y o u c a n e x t e n d t h e s i m p l e m o d e l o f t r a c e a b i l i ty ta b l e sb y d i s t i n g u i s h in g b e t w e e n t h e t y p e s o f r e l a t i o n s h ipb e t w e e n r e q u i r e m e n t s a n d b y i n d i c a t in g e a c h o f t h e se ,u s in g a d i f f e r en t s y mb o l , i n each t ab l e ce l l . Po s s ib l e r e l a -t i o n s b e t w e e n r e q u i r e m e n t s w h i c h m i g h t e x i s t a r e a sfo l lows .

1 s p e c i f ie s / i s- s p e c i fi e d - b y . T h i s r e l a t i o n i n d i c a t e s t h a t s o m er e q u i r e m e n t B a d d s d e t a i l t o a n o t h e r r e q u i r e m e n t A . F o re x a m p l e , i f A is a g e n e r a l s e c u r i t y r e q u i r e m e n t w h i c hs t a t e s t h a t d a t a s h o u l d b e e n c r y p t e d , B m i g h t s p e c i f y t h ec h a r a c te r i st ic s o f t h e e n c r y p t i o n a l g o ri th m w h i c h s h o u l db e u s e d .

2 r e q u i r e s / i s - r e q u i r e d - b y . T h is r e l a t i o n i n d i c a t e s t h a t s o m er e q u i r e m e n t B r e q u i re s t h e r e s u lt p r o v i d e d b y s o m e o t h e rr e q u i r e m e n t A . F o r e x a m p l e , A m i g h t s p e c if y t h a t t h es y s te m s h o u l d m a i n t a i n a r e c o r d o f t h e c u r r e n t t im e a n dd a t e i n s o m e s p ec i f ic f o r ma t ; B m ig h t s p ec i f y t h a t ea cht r a n s a c t i o n p r o c e s s e d b y t h e s y s t e m s h o u l d b e d a t es t a m p e d .

3 c o n s t r a i n s / i s - c o n s t r a i n e d b y . T h i s r e l a t i o n i n d i c a t e s th a ts o m e r e q u i r e m e n t B i s c o n s t r a i n e d b y s o m e o t h e r r e q u i r e -m e n t A . F o r e x a m p l e , B m i g h t s p e c i f y t h a t s o m e r e a lv a l u e s h o u l d b e d i s p l a y e d a n d A m i g h t s t a t e t h a t a l l r e a ln u m b e r s s h o u l d b e i m p l e m e n t e d a s 1 2 - d i g i t f i x e d - p o i n tn u m b e r s .


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Define Traceability Policies 229I f y o u h a v e a r e l a t iv e l y s m a l l n u m b e r o f r e q u i r e m e n t s ( upt o 2 5 0 , s a y ) , y o u c a n i m p l e m e n t a n d m a n a g e t r a c e a b i l i t yt a b l e s u s i n g a s p r e a d s h e e t . T r a c e a b i l i t y t a b l e s b e c o m em o r e o f a p r o b l e m w h e n y o u h a v e h u n d r e d s o r t h o u s a n d so f r e q u i r e m e n t s a s y o u e n d u p w i t h v e r y la rg e a n d t h i n l yp o p u l a t e d t a b l e s . S o m e t i m e s , d e p e n d e n c i e s b e t w e e nr e q u i r e m e n t s a r e c o n f i n e d t o r e q u i r e m e n t s g r o u p s a n dy o u c a n c r e a t e s e p a r a t e t r a c e a b i l i t y ta b l e s f o r t h e s eg r o u p s . D e p e n d e n c i e s a c r o ss g r o u p s c a n b e s p e c i f ie ds e p a r a t e ly . I f t h i s is n o t t h e c a s e , w e r e c o m m e n d t h a to t h e r t r a c e a b i l i t y t e c h n i q u e s s u c h a s t r a c e a b i l i t y l i s t ss h o u l d b e u s e d .

A c o m m o n e r r or w h i c h a r is e s w i t h t h e u s e o f t r a ce a b i l-i ty t a b le s is c o n f u s i o n b e t w e e n t h e r o w s a n d c o l u m n s .T h e r e f o r e , r a t h e r t h a n f i l l i n g i n R o w R 1 w h i c h s h o w s t h a tR 1 d e p e n d s o n R 3 a n d R 3 , c o l u m n R 1 i s f i l l e d i ns h o w i n g t h a t R 3 a n d R 4 a r e d e p e n d e n t o n R 1 . O b v i o u s l y ,t h e se d o n o t m e a n t h e s a m e t h i ng a n d c a n c a u s ep r o b l e m s t o u s e r s o f t h e t r a c e a b i l i t y ta b l e s.

Traceabi l i ty l is tsT r a c e a b i l i t y l is t s a r e a s i m p l i f i e d f o r m o f t r a c e a b i l i t y t a b lew h e r e , a l o n g w i t h e a c h r e q u i r e m e n t d e s c r i p t i o n , y o u k e e po n e o r m o r e l i st s o f t h e i d e n t i f i e r s o f r e l a t e d r e q u i r e -m e n t s . T r a c e a b i l i t y l i s t s a r e m o r e c o m p a c t t h a n t r a c e a b i l -i ty t a b le s a n d d o n o t b e c o m e a s u n m a n a g e a b l e w i t h l a rg en u m b e r s o f r e q u i r e m e n t s . T h e y a re p r o b a b l y le s s p r o n e t oe r r o r t h a n t r a c e a b i l i t y t a b l e s .

RequirementR1R2R3R4R5

Depends onR3, R4R5, R6R4, R5

R2R6

Figu re 9.3 A traceability list


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230 Requirements Managem entT r a c e a b i l i ty l is ts a r e s i m p l e l is ts o f r e l a t i o n s h i p s w h i c hc a n b e i m p l e m e n t e d a s t e x t o r a s s i m p l e t a b l e s . F i g u r e 9 . 3s h o w s a t r a c e a b i li ty l i st f or t h e d e p e n d e n c i e s s h o w n i nFigure 9 .2 .Yo u m a y u s e s e v e ra l l i s ts , o n e f o r e a c h t y p e o f r e l a t i o n -s h i p s u c h a s requires, is-required-by, specifies, etc . , orm a y s i m p l y k e e p a s i n gl e l is t of r e l a t e d r e q u i r e m e n t s . T h ed i s a d v a n t a g e o f t h e s e l is ts c o m p a r e d to t r a c e a b il i ty t a b le sis t h a t t h e r e i s n o e a sy w a y t o a s se s s t h e i n v e r se o f a r e l a-t i o n s h i p . W e c a n e a s i l y s e e t h a t R 1 i s d e p e n d e n t o n R 3a n d R 4 b u t , g i v e n R 4 , w e m u s t l o o k t h r o u g h t h e w h o l et a bl e to s ee w h i c h r e q u i r e m e n t s d e p e n d o n it. I f y o u w i s ht o m a i n t a i n t h i s ' b a c k w a r d - t o ' i n f o r m a t i o n , y o u n e e d t oc o n s t r u c t a n o t h e r t a b l e s h o w i n g t h e s e r e l a t i o n s h i p s .T r a c e a b i l i t y l i s t s c a n e i t h e r b e m a i n t a i n e d m a n u a l l y a sw o r d p r o c e s s o r o r s p r e a d s h e e t t a b l e s o r c r e a t e d f r o m t h er e q u i r e m e n t s d a t a b a s e . T o c r e a t e t h e l i s t a u t o m a t i c a l l y ,t h e d a t a b a s e r e c o r d f o r e a c h r e q u i r e m e n t m u s t i n c l u d e al i n k t o a l is t o f r e l a t e d r e q u i r e m e n t s .

Costs and problemsT h e c o s t o f i n t r o d u c i n g t h i s g u i d e l i n e i n to y o u r r e q u i r e -m e n t s e n g i n e e r i n g p r o c e s s a r e c o m p a r a b l e w i t h t h e c o s t so f d e f i n i n g a n y o t h e r s i g n i fi c a n t q u a l it y m a n a g e m e n tp r o c e d u r e . S e v e ra l m o n t h s o f c a l e n d a r t i m e m a y ben e e d e d f o r c o n s u l t a t i o n , a n d s i g n i f i c a n t e f f o r t i s r e q u i r e dt o e n s u r e t h a t h i g h - q u a l i t y p o l i c i e s a r e d e f i n e d a n dr e v i e w e d . O n c e t h e s e p r o c e d u r e s h a v e b e e n a g r e e d , t h e r ea re s o m e m a i n t e n a n c e c o st s as y o u i n t r o d u c e c h a n g e sb a s e d o n e x p e r i e n c e w i t h t h e m . M a k i n g t h e s e c h a n g e ss h o u l d n o t n o r m a l l y b e a n e x p e n s i v e p r o c e s s .T h e c o s ts o f i m p l e m e n t i n g t r ac e a b il it y d e p e n d s o n t hes p e c i f i c t r a c e a b i l i t y p o l i c i e s a n d o n t h e n u m b e r o fr e q u i r e m e n t s f or y o u r s y s t e m . U n f o r t u n a t e l y , t h e c o s t s o ft r a c e a b i li ty i n c r e a s e d i s p r o p o r t i o n a t e l y a s t h e n u m b e r o fr e q u i r e m e n t s i n c r e a s e . T h e r e f o r e , w h i l e t h e c o s t s o fi m p l e m e n t i n g f a i r l y c o m p r e h e n s i v e t r a c e a b i l i t y p o l i c i e sm a y b e m o d e r a t e f o r a s m a l l s y s t e m , t h e s a m e p o l i c i e sm a y be i m p r a c t i c a l l y e x p e n s i v e f or l ar g e s y s t e m s . Y o un e e d t o d e r i v e sp e c i f i c t r a c e a b i l i t y p o l i c i e s f ro m y o u rg e n e ra l p o l i c i e s , a s d i s c u s se d i n Gu i d e l i n e 9 . 4 .


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Define Traceabil ity Policies 231T h e m a i n p r o b l e m t h a t y o u a r e l i k e l y t o e n c o u n t e r i sd o u b t s a b o u t th e v a l u e o f p r o c e d u r e s w h i c h d o n o tp r o v i d e a n i m m e d i a t e b e n e f i t ( s e e t h e d i s c u s s i o n i n t h ei n t r o d u c t i o n ) a n d s o m e r e s i s t a n c e , p e r h a p s , t o i m p l e m e n t -

i n g t h e s e p r o c e d u r e s . P e o p l e m a y h a v e h a d p r e v i o u sexpe r i ence wi t h t r aceab i l i t y p r ob l em s and t he d i f f i cu l t i e spos ed by m anag i ng l a r ge vo l um es o f t r aceab i l i t y i n fo r m a-t ion . You mus t be r ea l i s t i c about what t r aceab i l i ty in for -m a t i o n c a n b e m a i n t a i n e d ; y o u s h o u l d n o t a s k a n a l y s t s t or e c o r d i n f o r m a t i o n w h i c h w i l l n e v e r b e u s e d . Y o u m u s ta l so s t r e s s t he l ong - t e r m benef i t s o f t r aceab i l i ty a ndconv i nce peo p l e (by exa m p l e i f pos s ib l e ) o f t he bene f i t so f m a i n t a i n i ng t h i s i n fo r m a t i on .


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Key benefit

Costs of introductionCosts of applicationGuidel ine type

Acts as a central record of allproject-specific traceabili tyinformationLowMo d e ra t e - h i g hBasic

A t r a c e a b i l i t y m a n u a l i s a s u p p l e m e n t t o t h e r e q u i r e m e n t sd o c u m e n t w h i c h i n c l u d e s t h e s p e c i f i c t r a c e a b i l i t y p o l i c i e su s e d i n a p r o j e c t a n d a l l r e q u i r e m e n t s t r a c e a b i l i t y i n f o r -m a t i o n . T h is d o c u m e n t is u s e d b y r e q u i r e m e n t s e n g i n e e r sa n d s y s t e m d e v e l o p e r s .

Benefits T e a m m e m b e r s c a n e a s il y f i n d t h e sp e c i fi c t r a c e a b i li t y

p o l i c i e s f o r t h e i r p ro j e c t A t r a c e a b i li ty m a n u a l k e e p s al l t r a c e a b i li t y i n f o r m a t i o n i no n e p l a c e a n d m a k e s i n f o rm a t i o n ( r e l a t i v e l y ) e a sy t o f i n d

a n d u p d a t e . T h e sp e c i f i c t r a c e a b i l i t y p o l i c ie s u s e d i n a p ro j e c t a rem a d e a v a i l a b l e t o a l l p r o j e c t m e m b e r s t h r o u g h t h e t r a c e -

a b i l i t y m a n u a l . F o r s y s t e m s w h e r e a s a fe t y o r s e c u r i t y c a s e m u s t be m a d ea t r a c e a b i l i t y m a n u a l m a y b e u s e d t o s h o w t h a t c o m p o -n e n t s a re i n d e p e n d e n t o r to a rg u e t h a t c o m p o n e n t f a il ur ec a n n o t p r o p a g a t e i n a n u n c o n t r o l l e d w a y .Implementation

T h e t r a c e a b i l i t y m a n u a l i s a c e n t r a l r e c o rd o f t h e t r a c e -ab i l i ty po l i c i e s fo r a spec i f i c p ro jec t an d a l l o f the re l e -v a n t t r a c e a b i l i t y i n f o rm a t i o n . Yo u r g e n e ra l t r a c e a b i l i t yp o l i c i e s s h o u l d b e s p e c i a l i s e d t o t a k e i n t o a c c o u n t t h ec h a ra c t e r i s t i c s o f t h e p ro j e ct . T h i s m a y i n v o l v e l e a v i n g


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M a i n t a i n a T r a c e a b i li ty M a n u a l 2 3 3o u t s o m e t r a c e a b i l i t y i n f o r m a t i o n , d e c i d i n g o n e x a c t l yh o w t r a c e a b i l i t y i n f o r m a t i o n s h o u l d b e r e p r e s e n t e d ,d ec id in g o n th e r e s p o n s ib i l i t i e s f o r t r aceab i l i t y i n f o r ma-t ion co l lec t ion , e tc .

T h e s p e c i f i c t r a c e a b i l i t y p o l i c i e s w h i c h s h o u l d b e u s e df or a p r o j ec t d e p e n d s o n a n u m b e r o f f ac to r s. T h es ef ac to r s i n c lu d e th e f o l lo w in g .1 N u m b e r o f r e q u i r e m e n t s. T h e g r e a t e r t h e n u m b e r o fr e q u i r e m e n t s , t h e m o r e t h e n e e d f o r f o r m a l t r a c e a b i l i t yp o l i c ie s . H o w ev er , i f t h e r e a r e a v e r y l a r g e n u m b e r o fr e q u i r e m e n t s , y o u h a v e t o b e r e a l i s t i c a b o u t w h a t t r a c e -a b i l i t y p o l i c i e s c a n b e i m p l e m e n t e d i n p r a c t i c e . C o m p l e t e

r e q u i r e m e n t s - d e s i g n t r a c e a b i l it y is im p r a c t i c a l f or m o s tla rge sys tems .2 E s t i m a t e d s y s te m l i fe t i m e . M o r e c o m p r e h e n s i v e t r a c e -a b i l i t y p o l i c i e s s h o u l d b e d e f i n e d f o r s y s t e m s w h i c h h a v ea long l i f e t ime.3 L e v e l o f o r g a n i sa t i o n a l m a t u r i t y . D eta i l ed t r aceab i l i t ypo l ic ies a re mos t l ike ly to be cos t - ef f ec t ive in o rgan isa-

t i o n s w h ich h av e a h ig h e r l ev e l o f p r o ces s ma tu r i t y . O r g a -n i s a t i o n s a t t h e b a s i c m a t u r i t y l e v e l s h o u l d f o c u s o ns i m p l e r e q u i r e m e n t s - r e q u i r e m e n t s t r a c e a b i l i t y .4 P r o je c t t e a m si z e a n d c o m p o s i t io n . W i t h a s m a l l t e a m ,i n f o r m a l d i s c u s s i o n s b e t w e e n t e a m m e m b e r s m a y b e a l lt h a t is r e q u i r e d t o a s se s s t h e i m p a c t o f p r o p o s e d c h a n g e s .W i t h la r g er t e a m s , h o w e v e r , y o u n e e d m o r e f o r m a l a n dd e t a i l ed t r aceab i l i t y p o l i c i e s . T h i s i s p a r t i cu l a r ly t r u e i f

a l l m em b er s o f t h e t ea m a r e n o t l o ca t ed to g e th e r .5 T y p e o f s y s t e m . Cr i t i ca l s y s t ems s u ch a s h a r d r ea l - t imeco n t r o l s y s t ems o r s a f e ty - c r i t i ca l s y s t ems n eed mo r e co m-p r e h e n s i v e t r a c e a b i l i t y p o l i c i e s t h a n n o n - c r i t i c a l s y s t e m s .

T h e t r a c e a b i l i t y m a n u a l s h o u l d n o r m a l l y b e d e v e l o p e di n c r e m e n t a l l y a s t h e s y s t e m i s s p e c i f i e d , d e s i g n e d a n di m p l e m e n t e d . T h e f i r s t c h a p t e r s h o u l d a l w a y s i n c l u d e t h ep r o j e c t t r a c e a b i l i t y p o l i c i e s . R e q u i r e m e n t s d e p e n d e n c i e sc a n t h e n b e d o c u m e n t e d a s s o o n a s t h e r e q u i r e m e n t sd o c u m e n t i s a g r e e d b u t d e s i g n t r a c e a b i l i t y , d o c u m e n t a -t i o n t r aceab i l i t y , e t c ., m u s t b e ad d e d a t l a t e r s tag es o f t h ed e v e l o p m e n t p r o c e s s .


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234 Requirements Managem entT r a c e a b i l i ty i n f o r m a t i o n m u s t b e r e g u l a r l y u p d a t e d i f i tis t o r e m a i n u s e f u l . I f t h e d o c u m e n t i s m a i n t a i n e d o np a p e r , t h e r e w i l l a l w a y s b e a la g b e t w e e n c h a n g e s m a d et o t h e p a p e r d o c u m e n t a n d t h e d o c u m e n t w h i c h i s u s e d

b y t h e e n g in e e r s m a i n t a i n i n g t h e r e q u i r e m e n t s a n d / o r t hes y s t em . F u r t h e r m o r e , if a d o c u m e n t e x is t s on p a p e r , t h e r ei s a l wa y s a t e m p t a t i o n t o u se t h i s , e v e n i f i t i s o u t -o f -d a te . T h i s o f t e n r e s u l t s i n e r ro r s o r m i s u n d e r s t a n d i n g s .W e s t r o n g l y r e c o m m e n d t h a t t h e t r a c e a b i l i t y m a n u a ls h o u l d b e i m p l e m e n t e d a s a n e t w o r k e d e l e c tr o n i c d o c u -m e n t r a t h e r th a n a s a p a p e r d o c u m e n t . W h e n t r ac e a b il it yi n f o r m a t i o n i s r e q u i r e d , t h e d o c u m e n t i s e i t h e r c o n s u l t e do n - s c r e e n o r t h e r e l e v a n t s e c t i o n s o f t h e d o c u m e n t a r ep r i n t e d . S o m e k i n d o f h y p e r t e x t s y s t e m (e .g . a W W W -b a s e d s y s te m ) m a y b e u s e d t o im p l e m e n t t h e m a n u a l o r ,a l te r n a ti v e ly , i t m a y s i m p l y b e m a i n t a i n e d a s w o r d p r o c es -so r te x t. T h e re w i l l b e a d i f f e r e n t v e r s i o n o f t h e t r a c e -a b i li ty m a n u a l f or e a c h d i f f e r e n t v e r s i o n o f t h e s y s t e m .T h e t r a c e a b i l i t y m a n u a l , t h e r e f o r e , s h o u l d b e m a n a g e du s i n g y o u r n o r m a l c o n f i g u r a t i o n m a n a g e m e n t p r o c e d u r e s .T o e n s u r e t h a t t h e t r a c e a b i l i t y m a n u a l i s k e p t u p - t o -d a t e , y o u s h o u l d a s s i g n s o m e o n e t o b e t h e t r a c e a b i l i t ym a n u a l m a n a g e r . H e o r s h e s h o u l d w o r k w i t h s y s t e md e v e l o p e r s t o e n s u r e t h a t c h a n g e s t o t h e r e q u i r e m e n t s /d e s i g n , e t c . , h a v e b e e n i n c o r p o r a t e d i n t h e m a n u a l a n ds h o u l d r e v i e w a n d u p d a t e t r a c e a b i l i t y p o l i c i e s . T h e t r a c e -a b i l i t y m a n u a l m a n a g e r s h o u l d a l s o b e r e s p o n s i b l e f o rf o l lo w i n g u p d e v i a t i o n s f r o m t r a c e a b i li ty p o l i c i e s a n de n s u r i n g t h a t t h e r e q u i r e d i n f o r m a t i o n i s s u b s e q u e n t l ya d d e d t o t h e t r a c e a b i l i t y m a n u a l .

Costs and problem sI f y o u h a v e a s e t o f o rg a n i sa t i o n a l t r a c e a b i l i t y p o l i c i e s a sr e c o m m e n d e d i n G u i d e l i n e 9 . 3 , t h e r e a r e r e l a t i v e l y l o wc o s t s i n v o l v e d i n i n t r o d u c i n g t h i s g u i d e l i n e . H o w e v e r , i tc a n b e e x p e n s i v e t o m a i n t a i n a t r a c e a b i l i t y m a n u a l . F o rl a r g e s y s t e m s , m a i n t a i n i n g t h e t r a c e a b i l i t y m a n u a l i sl i k e l y t o b e a f u l l - t i m e jo b a n d , e v e n f o r r e l a t i v e l y sm a l ls y s t e m s , y o u m u s t a l lo c a te a t l e a st 2 5 % o f s o m e o n e ' st im e f or t r ac e a b i li ty m a n u a l m a n a g e m e n t . A s d i s c u s s e da b o v e , th e c o s t s o f c o l l e c t i n g t h e t r a c e a b i l i t y i n f o rm a t i o n


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M a i n t a i n a T r a c e a b i li ty M a n u a l 2 3 5i t se l f a r e o b v i o u s l y s i g n if i c a n t a n d d e p e n d e n t o n t h en u m b e r o f r e q u i r e m e n t s .T h e m a i n p r o b l e m y o u w i l l f i n d i s k e e p i n g t h e t r a c e -a b i l i t y m a n u a l u p t o d a t e . W h e n p e o p l e a r e w o r k i n gu n d e r p r e s s u r e t o m a k e s y s t e m c h a n g e s , t h e y w i l l f o r g e tt o m a k e a m e n d m e n t s t o t h e t r a c e a b i l i t y m a n u a l a s t h e s ea r e n o t c r i t i ca l f o r t h e ch an g e to b e mad e to t h e s y s t em.T h e r e i s a l w a y s a t e m p t a t i o n t o d e v i a t e f r o m t r a c e a b i l i t yp o l i c i e s b e c a u s e o f t h e n e e d t o d e l iv e r o n s c h e d u l e . I ft h i s h a p p e n s i n a n u n c o n t r o l l e d w a y , t h e t r a c e a b i l i t ym a n u a l w i ll , fa i rl y r a p i d l y , b e c o m e u s e l e s s.


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236 Requirements Managem ent

K e y b e n e f i t M a k e s i t e a s i e r t o m a n a g ela rge num bers of requirementsCosts of in t roduc t ion M odera te -h ighCosts of app l icat ion ModerateG u i d e l i n e type Intermediate

Benefits

R a t h e r t h a n m a i n t a i n i n g r e q u i r e m e n t s i n t e x t d o c u m e n t s ,e s t a b l i s h a r e q u i r e m e n t s d a t a b a s e a n d s t o r e t h e i n d i v i d u a lr e q u i r e m e n t s a s e n t r i e s i n t h i s d a t a b a s e .

M a n a g i n g r e q u i r e m e n t s i n a d a t a b a s e m a k e s i t e a s i e r tom a i n t a i n l i n k s b e t w e e n i n d i v i d u a l r e q u i r e m e n t s a n d t os e a r c h f o r a n d a b s t r a c t r e l a t e d g r o u p s o f r e q u i r e m e n t s .

I f t h e d a t a b a s e is a g e n e r a l - p u r p o s e r e p o s i t o r y f or s y s t e mi n f o r m a t i o n , l i n k s f r o m t h e r e q u i r e m e n t s t o d e s i g n a n di m p l e m e n t a t i o n i n f o r m a t io n m a y be m a i n t a i n e d . I f t h e d a t a b a s e s u p p o r t s c o n c u r r e n t w o r k i n g , i t a l l o w s f ord i f f e r e n t g r o u p s t o w o r k o n t h e r e q u i r e m e n t s s p e c i f i c a t i o na t t h e s a m e t i m e w i t h o u t g e n e r a t i n g r e q u i r e m e n t s i n c o n -

s i s t e nc i e s . D a t a ba s e f a c i l i t i e s fo r da t a ba c kup , i n t e g r i t ya n d s e c u r i t y m e a n t h a t r e q u i r e m e n t s e n g i n e e r s n e e d n o tb e c o n c e r n e d w i t h t h e s e i s s u e s . T h e r e q u i r e m e n t s m a y b e a u t o m a t i c a l ly p r o c e s s e d toe x t r a c t p a r t i c u l a r t y p e s o f i n f o r m a t i o n . F o r e x a m p l e , i tm a y b e p o s s i b l e t o g e n e r a t e t r a c e a b i l i t y t a b l e s a n d l i s t sa u t o m a t i c a l l y f r o m i n f o r m a t i o n i n t h e r e q u i r e m e n t s d a t a -base .

Implementa t ionT h e m o s t a p p r o p r i a t e w a y t o i m p l e m e n t t h i s g u i d e l i n ed e p e n d s o n th e t y p e a n d t he n u m b e r o f r e q u i r e m e n t s


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U se a Da ta ba s e to M a na ge R e qu i r e me nts 2 3 7which must be managed and the particular ways ofworking in your organisation. Issues which influencedesign choices are as follows.

1 How are requi rements expressed? Do you use natural lan-guage, graphical models, mathematical expressions, etc.?Do you need to store additional information such as pho-tographs as part of the requirements rationale? If youneed to store more than just simple text, you may need touse a database with multi-media capabilities.2 How many requirements do you typically need tomanage? Is it tens, hundreds, thousands or tens of thou-sands? The requirements for a small to medium sizedsystem can be managed using commercial PC databases.Larger systems usually need a server-based system and adatabase, such as ORACLE, which is designed to managea very large volume of data.3 Are the requirements always developed and managed byteams which work together at the same site and whichuse the same types of computers or do you need to access

the requirements database from different sites? If youneed multi-site access from different types of equipment,you should using an Intranet-based solution which pro-vides access to the requirements database through aWWW browsing system.4 Do you already use a database for software engineeringsupport? Do you have a company policy on database use?What types of computer do you use? These factors

obviously constrain the type of database which you canu s e .5 What in-house database expertise do you have available?Will requirements engineers be responsible for databaseadministration or will this be a separate responsibility?Database management costs can be high and a solutionwhich requires a specialist database administrator maynot be cost-effective.

If you maintain your requirements in a database, you candesign the requirements database to include traceabilityinformation. With each requirement in the database, youshould include at least two fields for traceability informa-


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238 Requirements M anagem entt i o n . T h e s e s h o u l d b e f i l l e d i n w i t h r e f e r e n c e s t o o t h e rr e q u i r e m e n t s w h i c h t h e r e q u i r e m e n t d e p e n d s o n a n dw i t h r e f e r e n c e s t o r e q u i r e m e n t s w h i c h a r e d e p e n d e n t o nt h a t re q u i r e m e n t . O b v i o u s l y , if y o u w i s h t o m a i n t a i no t h e r t y p e s o f t r a c e a b i l it y i n f o r m a t i o n s u c h a s re q u i re m e n t s - a r c h i t e c t u r e l i n k s , y o u m u s t i n c l u d e d a t a b a s e f i e l d st o r e c o r d i n f o r m a t i o n a b o u t e a c h d i f fe r e n t t y p e o f r e la -t i o n s h i p .U s i n g t h e d a t a b a s e s y s t e m h a s t h e a d v a n t a g e t h a t t h ed a t a b a s e i ts e l f u s u a l l y i n c l u d e s f a c il it ie s f o r b r o w s i n g a n dr e p o r t g e n e r a t i o n . Y o u c a n b r o w s e t h e r e q u i r e m e n t s i nt h e d a t a b a s e t h e n m o v e i m m e d i a t e l y t o r e l a t e d r e q u i r e -m e n t s . Y o u m a y a l s o w r i t e s i m p l e s c r i p t s w h i c h s c a n t h ed a t a b a s e a n d g e n e r a t e t h e s p e c i f i c t r a c e a b i l i t y i n f o r m a t i o nw h i c h y o u r e q u i r e .R e l a t i o n a l d a t a b a s e s a r e n o w t h e m o s t c o m m o n l y u s e dt y p e o f d a t a b a s e . R e l a t i o n a l d a t a b a s e s w e r e d e s i g n e d f o rs to r in g a n d m a n a g i n g la rg e n u m b e r s o f r e c o r d s w h i c hh a v e t h e s a m e s t r u c t u r e a n d m i n i m a l l i n k s b e t w e e n t h e m .A r e q u i r e m e n t s d a t a b a s e , h o w e v e r , m a y h a v e r e l a t i v e l yf e w r e c o r d s ( h u n d r e d s r a t h e r t h a n h u n d r e d s o f t h o u -s a n d s) e a c h o f w h i c h i n c l u d e s m a n y l in k s s u c h a s l in k st o d o c u m e n t s , t e x t f i l e s a n d o t h e r r e q u i r e m e n t s . M a i n t a i n -i ng t he s e l i nks i s pos s i b l e w i t h a r e l a t i ona l da t a ba s e .H ow e ve r , i t i s i ne f f i c i e n t a s i t r e qu i r e s ope r a t i ons ons e ve r a l d i f f e r e n t t a b l e s . F o r ve r y l a rge nu m be r s o f r e qu i r e -m e n t s , y o u m a y f i n d t h a t t h i s t y p e o f d a t a b a s e is t o oslow.T o u s e a r e l a t i o n a l d a t a b a s e , y o u m a y h a v e t o k e e p t h et e x t o f t he r e qu i r e m e n t s i n a s e pa r a t e f i le o r f il e s a nda c c e s s t h e s e f i l e s t h r o u g h t h e d a t a b a s e . T h e d a t a b a s et a b l e s ( w h i c h u s e t h e r e q u i r e m e n t s i d e n t i f i e r s a s k e y s ) a r eu s e d t o i n d e x r e q u i r e m e n t s a n d t o s t o r e l i n k s b e t w e e nr e l a t e d r e q u i r e m e n t s . Y o u f i n d l i n k e d r e q u i r e m e n t s u s i n gt he r e l a t i ona l j o i n ope r a t i on .O b j e c t - o r i e n t e d d a t a b a s e s h a v e b e e n d e v e l o p e d r e l a -t i v e l y r e c e n t l y a n d a r e s t r u c t u r a l l y m o r e s u i t e d t o r e q u i r e -m e n t s m a n a g e m e n t . T h e y a l l o w d i f f e r e n t t y p e s o fi n f o r m a t i o n t o b e m a i n t a i n e d i n d i f f e r e n t o b j e c t s a n dma na g i ng l i nks be t w e e n ob j e c t s i s f a i r l y s t r a i gh t fo r w a r d .H o w e v e r , t h is t y p e o f d a t a b a s e is st il l i m m a t u r e a n d l o w -c o s t o b j e c t - o r i e n t e d d a t a b a s e s a r e n o t w i d e l y a v a i l a b l e .


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Use a D a t ab ase t o M an a g e R eq u i rem en t s 239They are also probably more expensive to manage thanrelational databases.If you have a very large number of requirements, youwill need to use a powerful database management systemsuch as ORACLE. This might be organised as a databaseserver on a workstation with access through other clientworkstations or PCs. This is an expensive approach butthe power of these systems allows for fast databasemanipulation. They also usually have excellent reportgeneration tools which can be used to create skeletalrequirements documents from the requirements database.These databases can support many simultaneous usersand provide good facilities for backup and recovery in theevent of system failure.Lower-cost approaches are possible using simpler PCdatabase systems. Modern PC databases include facilitiesfor managing multimedia information such as diagramsand photographs. Some of them can use object sharingfacilities (such as OLE) to link directly to word processorfiles where the requirements text is stored. Their supportfor simultaneous access may be limited to locking thewhole database when it is in use and they have limitedfacilities for error recovery. The requirements databasemust provide shared access and access control to therequirements.Whatever database you use, some data administrationwill be required. The data administrator must set up andmanage the database schema. He or she should also beresponsible for executing backup and recovery proceduresand providing support to database users. Database admin-istration can take up quite a lot of time; a large require-ments database may need several hours per week of aprofessional database administrator s time.If you require access to your requirements databasefrom remote sites and using a variety of different compu-ters, you might consider using WWW-based informationsystem as a front-end for a requirements database server.At the time of writing, various off-the-shelf solutions ofthis type have just become available. We do not know ofany experience reports of using this type of informationsystem for requirements management but it is an interest-ing development which has significant future potential.


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240 Requirements Managem entA r e q u i r e m e n t s d a t a b a s e m a y b e u s e d i n c o n j u n c t i o nw i t h s p e c i a l - p u r p o s e C A S E t o o l s f o r r e q u i r e m e n t sm a n a g e m e n t . T h e r e a r e n o w s e v er a l of t h e s e t oo l s o n th em a r k e t , r a n g i n g f r o m s i m p l e P C s y s t e m s t o l a r g e a n d

c o m p l e x w o r k s t a t i o n - b a s e d t o o l s i n t e n d e d t o m a n a g el a r g e r e q u i r e m e n t s d a t a b a s e s . T h e s e t o o l s p r o v i d e b u i l t - i nt ra c e a b i li ty s u p p o r t a n d s o m e o f t h e m s u p p o r t t h e a u t o -m a t i c c r e a t io n o f r e q u i r e m e n t s d a t a b a s e s f r o m a n a t u r a l -l a n g u a g e r e q u i r e m e n t s d o c u m e n t . W e d o n o t e n d o r s e a n ys p e c if ic t o o l b u t i n c l u d e d e t a i ls o f t o o l s u p p l i e r s i n t h eb o o k ' s W W W p a g e s .

Costs and problem sT he r e i s a s i gn i f i c a n t c os t i nvo l ve d i n s e t t i ng up ar e q u i r e m e n t s d a t a b a s e a n d p u t t i n g p r o c e d u r e s i n p l a c e t oe n s u r e t h a t i t i s u s e d . U s i n g s p e c i a l - p u r p o s e t o o l so b v i o u s l y i n c u r s s o m e c a p i t a l c o s t s a n d t r a i n i n g c o s t s t op u t t h e s e s y s t e m s i n t o u s e . I t i s u n l i k e l y t h a t y o u w i l lr e c o v e r a ll o f t h e s e c o st s f ro m i m p r o v e d r e q u i r e m e n t sm a n a g e m e n t i n a si n g le p r o je c t. T h e b e n e f i ts o f t h i sg u i d e l i n e w i l l o n l y e m e r g e a f t e r t h e d a t a b a s e i s u s e d i nsevera l p ro jec t s .T h e c o s ts o f a p p l y i n g t h e g u i d e l i n e i n c l u d e t h e c o s ts o fd a t a b a s e a d m i n i s t r a t i o n a n d , o b v i o u s l y , d a t a e n t r y c o s t sf o r e n t e r i n g t h e r e q u i r e m e n t s i n t h e d a t a b a s e . T h e s e c o s t sa re p r o p o r t i o n a l to t h e n u m b e r o f r e q u i r e m e n t s to bem a n a g e d .

O n e o f t h e m a j o r p r o b l e m s w i t h a r e q u i r e m e n t s d a ta -b a s e i s l i n k i n g t h e d a t a b a s e t o t h e r e q u i r e m e n t s d o c u -m e n t . R e a d e r s o f t h e r e q u i r e m e n t s d o c u m e n t w i l l n o t b ep r e p a r e d t o u s e t h e d a t a b a s e d i r e c t l y s o y o u m u s t h a v ep r o c e d u r e s w h i c h w i l l a u t o m a t i c a l l y c r e a t e t h e r e q u i r e -m e n t s d o c u m e n t f r o m i n f o r m a t i o n i n t h e d a t a b a s e . T h i s i sb e c o m i n g m u c h e a s i e r a s i t i s p o s s i b l e i n s o m e d a t a b a s e st o l i nk d i r e c t l y t o w or d p r oc e s s o r f i l e s . I n o t he r c a s e s , t hed a t a b a s e i n f o r m a t i o n m a y b e p r o c e s s e d t o g e n e r a t e t h er e q u i r e m e n t s i n a s t a n d a r d w o r d p r o c e s s o r f o r m a t s u c h a sM i c r o s o f t ' s R T F f o r m a t o r i n H T M L , t h e f o r m a t t i n gl a n g u a g e f o r W W W d o c u m e n t s .I f y o u a r e p l a n n i n g t o u s e a d a t a b a s e f or r e q u i r e m e n t sm a n a g e m e n t , a d d i n g t r a c e a b i l i ty l in k s is r e la t iv e l y i n e x -


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Use a D a t ab ase t o Man ag e R eq u i rem en t s 241p e n s i v e . I f y o u a l r e a d y h a v e a d a t a b a s e a n d y o u h a v e n o td e s i g n e d t h e s e i n t o t h e d a t a b a s e s c h e m a , i t m a y b e v e r ye x p e n s i v e t o r e t r o f i t t h e m . A p r o b l e m w h i c h y o u m a ye n c o u n t e r i s t h a t m a n y d a t a b a s e s y s t e m s d o n o t a l l o wy o u t o c r e a t e f i e l d s w h i c h i n c l u d e m o r e t h a n o n e r e f e r -e n c e t o o t h e r d a t a b a s e r e c o r d s . M o s t r e q u i r e m e n t s ,h o w e v e r , w i l l i n c l u d e d e p e n d e n c i e s o n s e v er a l o t h e rr e q u i r e m e n t s , s o y o u m u s t g e t r o u n d t h i s l im i t a t i o n i ns o m e w a y .


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Key benefit Provides a framework forsystematically assessingchange proposalsC o s ts o f i n t r o d u c t i o n Moderate-highCosts of application Low-moderateG u i d e l i n e type Intermediate

You should define policies for managing changes torequirements which set out how changes are formallyproposed, analysed, and reviewed. Accepted changes arethen implemented to create a new version of the require-ments document.Benefits

Change management policies allow overall costs to becontrolled by ensuring that the whole life-cycle impact ofrequirements changes is taken into account. As requirements changes are proposed, there is a need tokeep track of the status of these changes and to be able toproduce reports on requirements evolution. Change management policies give stakeholders a formal

mechanism for proposing changes to requirements whichdoes not favour any specific group of stakeholders.

Imp lemen ta t ionChange management policies are concerned with theprocedures, processes and standards which are used tomanage changes to system requirements. Change manage-ment policies mean that similar information is collectedfor each proposed change and that overall judgements aremade about the costs and benefits of proposed changes.Without change management policies, you cannot be surethat proposed changes to the requirements add to the


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D efine C hang e Ma nagem ent Policies 243general services provided by the system and help supportbusiness goals (see Guideline 3.4, M a k e a b u s i n e s s c a s ef o r t h e s y s t e m .The change management policies which you establishshould define the following.

1 The change request process and the information requiredto process each change request.2 The process used to analyse the impact and costs ofchange and the associated traceability information.3 The membership of the body which formally considerschange requests.4 The software support (if any) for the change control pro-cess. We recommend that you develop a change manage-ment database where you store all change requests.Within this database, you should maintain informationabout the change request, its status and how it has beenimplemented.

Stakeholders should submit proposals for requirementschanges using a pre-defined form. This should includefields to collect information about the change and theimpact of the change on other requirements, the systemimplementation and other system documentation. Afterinitial filtering to remove changes which are a result ofstakeholder misunderstanding, the impact and the costsof the change are assessed. The change and its associatedcosts are then considered by some formal group (in mili-tary projects, this is called a change control board) whodecide whether or not the change to the requirementsshould be accepted.If possible, the change management process should besupported by software. There are now several systemsavailable which claim to support change management.Most of these are oriented towards software changecontrol and some are tightly integrated with commercialconfiguration management systems.Of course, you can use a general-purpose database tostore change requests, associated status information andlinks to the requirements themselves. You can also use e-mail for information distribution and circulation.


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244 Requirements Man agem entH o w e v e r , y o u h a v e t o t r a n s f e r i n f o r m a t i o n m a n u a l l y f r o mt h e e - m a i l s y s t e m t o t h e c h a n g e m a n a g e m e n t s y s t e m a n dth i s i s a p o t e n t i a l s o u r ce o f e r r o r an d d e l ay .I d e a l l y , y o u s h o u l d i n t e g r a t e a c h a n g e c o n t r o l s y s t e mw i t h a r e q u i r e m e n t s d a t a b a s e ( s e e G u i d e l i n e 9 . 5 ) . T h i ss h o u l d l e t y o u k e e p t r a c k o f t h e d i ff e r e n t v e r s i o n s o fr e q u i r e m e n t s a n d l i n k t h e p r o p o s e d c h a n g e s w i t h t h ei n it ia l r e q u i r e m e n t a n d a n y r e v i s io n o f t h a t r e q u i re m e n t .U n f o r t u n a t e l y , C A S E t o o l s f o r v e r s i o n a n d c o n f i g u r a t i o nm a n a g e m e n t a r e m o s t l y g e a r e d t o w a r d s m a n a g i n g f i l e s o fi n f o r m a t i o n ( s u c h a s s o u r c e p r o g r a m s ) r a t h e r t h a n r e l a -t i v e l y s h o r t , i n d i v i d u a l r e q u i r e m e n t s i n a d a t a b a s e . T om a n a g e t h i s i n f o r m a t i o n , y o u n e e d a v e r s i o n m a n a g e m e n ts y s t e m w h i c h c a n d e a l w i t h ' f i n e - g r a i n ' o b j e c t s . H o w e v e r ,y o u c a n c e r t a i n l y u s e a c o n v e n t i o n a l v e r s i o n m a n a g e m e n ts y s t e m t o m a n a g e r e v i s i o n s o f t h e r e q u i r e m e n t s d o c u -m e n t .Y o u c a n f i n d o u t m o r e a b o u t c h a n g e m a n a g e m e n t a n dm o r e g e n e r a l a s p e c ts o f c o n f ig u r a ti o n m a n a g e m e n t i nCh ap te r 3 3 o f Software Engineering ( I a n S o m m e r v i l l e ,A d d i s o n W e s l e y , 19 96 ). T h is i n c l u d e s a n e x a m p l e o f ac h a n g e r e q u e s t f o r m w h i c h m a y b e u s e d . W e h a v e a l s oi n c l u d e d i n f o r m a t i o n a b o u t s o m e c o m m e r c i a l c o n f i g u r a -t i o n m a n a g e m e n t s y s t e m s o n t h e b o o k ' s W W W p a g e s .

Costs and prob lemsD e f i n i n g a n d i m p l e m e n t i n g c h a n g e c o n t r o l p o l i c i e s i sf a i r l y e x p e n s i v e . Y o u m u s t a l l o w s e v e r a l m o n t h s f o r t h ec h a n g e m a n a g e m e n t p o l i c i e s t o b e d e f i n e d a n d b r o u g h tin to u s e . A f t e r i t h as b een in t r o d u ced , t h e co s t s o fr u n n i n g t h e s y s t e m a r e t h e c o s ts o f a s s e s s i n g th e i m p a c to f c h a n g e s a n d e n s u r i n g t h a t th i s i n f o r m a t i o n i s r e c o r d e di n t h e c h a n g e m a n a g e m e n t s y s t e m .I f y o u h a v e m a n a g e d r e q u i r e m e n t s c h a n g e s i n a n in f or -m a l w a y w h e r e s t a k e h o l d e r s d i s c u s s c h a n g e s d i r e c t l yw i t h r e q u i r e m e n t s e n g i n e e r s a n d s o f t w a r e d e v e l o p e r s , y o um a y f i n d r e s i s t a n c e t o th e s c h e m e f ro m b o t h o f t h e s eg r o u p s . T h e y m a y p e r c e i v e c h a n g e m a n a g e m e n t p o l i c i e sa s a n u n n e c e s s a r y o v e r h e a d w h i c h i n c r e a s e s t h e t i m en e e d e d t o i m p l e m e n t c h a n g e s . T o c o u n t e r t h i s , y o u m u s tm a k e c l e a r t h a t , i n t h e l o n g - t e r m , u n c o n t r o l l e d c h a n g e s


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Define Change M anag em ent Polic ies 2 4 5c os t a g r e a t de a l . T he y a r e l i ke l y t o l e a d t o a ' r e qu i r e -m e n t s d r i f t ' w h e r e t h e s y s t e m e v o l v e s t o w a r d s t h e n e e d so f t h o s e w h o a r e m o s t a b le to i n f l u e n c e t h e e n g i n e e r sr e s p o n s i b l e f o r s y s t e m e v o l u t i o n .

If y o u d o n ' t a u t o m a t e t h e c h a n g e m a n a g e m e n t p r o c es s,y o u w i l l p r o b a b l y h a v e i n f o r m a t i o n m a n a g e m e n tp r o b l e m s . T h e s e a r e n o t ju s t d u e t o t h e v o l u m e o f i n fo r -m a t i o n w h i c h m u s t b e p r o c e s s e d b u t a l s o d u e t o t h e f a c tt h a t c h a n g e p r o p o s a l s m u s t b e a n a l y s e d b y d i f fe r e n tp e o p l e . I t is v e r y e a s y to l o s e t ra c k o f w h e r e e a c h c h a n g er e que s t i s i n t he p r oc e s s .


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Key benef i t Finds the requirements wh ichare l ikely to be most expensiveto changeCosts of introd uctio n LowCosts of app l icat ion LowGu i d e l i n e type Intermediate

Benefits

G l o b a l s y s t e m r e q u i r e m e n t s a r e r e q u i r e m e n t s w h i c h s e to u t d e s i r a b l e o r e s s e n t i a l p r o p e r t i e s o f t h e s y s t e m a s aw h o l e . T h e y c a n n o t b e a s s i g n e d t o i n d i v i d u a l s u b -s y s t e m s o r m a p p e d o n to p a r t s o f t h e s y s t e m i m p l e m e n t a -t i o n . T h e s e r e q u i r e m e n t s s h o u l d b e e x p l i c i t l y i d e n t i f i e da n d d o c u m e n t e d a s p a r t of t h e re q u i r e m e n t s m a n a g e m e n tp r o ces s .

G l o b a l s y s t e m r e q u i r e m e n t s a r e v e r y e x p e n s i v e to c h a n g e .T h e c o s ts o f c h a n g e a r e h i g h b e c a u s e m a n y d i f f e r e n t p a r t so f t h e s y s t e m m a y b e a f fe c t e d b y t h e c h a n g e . I f t h er e q u i r e m e n t s c a n b e i d e n t i f i e d i n a d v a n c e , p a r t i c u l a ra t t e n t i o n c a n b e p a i d t o t h e i r a n a l y s i s a n d v a l i d a t i o n a n ds o e n s u r e t h a t f u t u r e r e q u i r e m e n t s c h a n g e s d u e t o o m i s -s io n s a n d m i s u n d e r s t a n d i n g s a r e m i n i m i s e d . T h e m a n a g e m e n t o f g lo b a l s y s te m r e q u i r e m e n t s is p a r ti -c u l a r l y c o m p l e x a s c h a n g e s t o t h e s e r e q u i r e m e n t s m a yi n v o l v e c o n s u l t a t i o n w i t h m a n y d i f f e r e n t c o n t r a c t o r s w h oa r e d e v e l o p i n g d i f fe r e n t p a r t s o f t h e s y s t e m . K n o w i n gg l o ba l r e q u i r e m e n t s s i m p l i f ie s t h e p l a n n i n g o f t h i s c h a n g ep r o ces s .

Implementat ionW e r e c o m m e n d t h a t y o u i d e n t i f y t h e g l o b a l r e q u i r e m e n t sd u r i n g t h e r e q u i r e m e n t s a n a l y s i s a n d t h e r e q u i r e m e n t sv a l i d a t i o n p r o c e s s e s . D u r i n g t h e s e a c t i v i t i e s , y o u a r e


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Identify G lobal System Requirements 2 4 7a n a l y s i n g a l l t h e r e q u i r e m e n t s s o v e r y l i t t l e a d d i t i o n a le f f o r t i s n eed ed to d i s co v e r g lo b a l r eq u i r emen t s . A l t e r n a -t i v e l y , y o u c a n i d e n t i f y g l o b a l r e q u i r e m e n t s w h e n y o u a r ec r ea t in g y o u r i n i t i a l t r aceab i l i t y i n f o r ma t io n .

T h er e i s n o eas y w ay to i d en t i f y g lo b a l s y s t em r eq u i r e -m e n t s . Y o u n e e d t o u s e y o u r j u d g e m e n t a n d k n o w l e d g eo f t h e s y s t em. T o h e lp w i th t h i s i d en t i f i ca t io n p r o ces s , i ti s s o m e t i m e s h e l p f u l t o a s k t h e fo l l o w i n g q u e s t i o n s a b o u te a c h r e q u i re m e n t .1 Is t h e r e q u i r e m e n t e x p r e s s e d i n a v e r y g e n e r a l w a y ( fo re x a m p l e , ' t h e s y s t e m m u s t n e v e r c o r r u p t d a t a i n t h e d a t a -base ' ) ?2 D o e s t h e r e q u i r e m e n t e x p r e s s s o m e g lo b a l, n o n - f u n c t i o n a ls y s t e m c h a r a c t e r i s ti c (fo r e x a m p l e , ' th e s y s t e m m u s t p r o -ces s N t r an s ac t io n s p e r s eco n d ' ) ?3 Is t h e r e q u i r e m e n t a g e n e r a l u s e r i n te r f a c e r e q u i r e m e n t ?4 D o es th e r eq u i r e m en t r e f e r t o s p ec i f i c s y s t em f u n c t io n -a l i t y o r a s p ec i f i c s y s t em s e r v i ce w h ich mu s t b e p r o -v i d e d ?5 C a n t h e r e q u i r e m e n t be m a p p e d o n to p a rt o f t h e sy s t e mm o d e l ?6 D o e s t h e r e q u i r e m e n t r e fe r t o s p e c if ic d a t a o r c o m p o n e n t so f t h e s y s t em?

I f t h e a n s w er s t o t h e q u es t io n s 1 - 3 a r e 'y es ' o r if t h ea n s w e r s t o q u e s t i o n s 4 - 6 a r e ' n o ' t h e n t h e r e q u i r e m e n tm a y b e a gl o ba l r e q u i r e m e n t . I f p o s s ib l e , y o u s h o u l d t r yt o i d e n t i f y g l o b a l s y s t e m r e q u i r e m e n t s d u r i n g a n a l y s i sa n d n e g o t i a t i o n a c t i v i t i e s . W h e r e t h i s i s i m p r a c t i c a l , t h e ym a y b e i d e n t i f i e d a t r e q u i r e m e n t s r e v i e w s d u r i n g t h e v a l i -d a t io n p r o ces s .Y o u w i l l n o t g e t t h e i d e n t i f i ca t io n o f g lo b a l s y s t emr e q u i r e m e n t s r i g h t f i r s t t i m e . S o m e r e q u i r e m e n t s w h i c ha p p e a r t o b e s u b - s y s t e m r e q u i r e m e n t s w i l l e m e r g e a sg l o b a l s y s t e m r e q u i r e m e n t s . Y o u m u s t t h e r e f o r e e x p e c tn e w g l o b a l r e q u i r e m e n t s t o b e d i s c o v e r e d t h r o u g h o u t t h er e q u i r e m e n t s a n a l y s i s , n e g o t i a t i o n a n d v a l i d a t i o np r o ces s es .G l o b a l s y s t e m r e q u i r e m e n t s r e a l l y r e q u i r e s e p a r a t e


34/39

248 Requirements Managementt r a c e a b i l i t y m a n a g e m e n t . T h e n o r m a l a p p r o a c h e s t o t r a c e -a b i l i t y w h e r e y o u l i n k s p e c i f i c r e q u i r e m e n t s o r r e q u i r e -m e n t s a n d s y s t e m c o m p o n e n t s d o n o t a p p l y t o t h e s er e q u i r e m e n t s . Y o u c a n n o t m a p t h e m o n t o a s e t o f s y s t e mc o m p o n e n t s . Y o u s h o u l d t h e r e f o r e m a i n t a i n a l i s t o fg lo b a l r eq u i r emen t s a s a s ep a r a t e s ec t io n in t h e t r aceab i l -i t y m a n u a l .

Costs and prob lemsT h e r e a r e n o s i g n i f i c a n t c o s t s i n v o l v e d i n i n t r o d u c i n g t h i sg u id e l in e . I f g lo b a l r eq u i r e m en t s a r e i d en t i f i ed a s p a r t o fo t h e r p r o c e s s e s s u c h a s a n a l y s i s a n d r e q u i r e m e n t sr e v i e w s , t h e a d d i t i o n a l c o st s o f a p p l y i n g t h e g u i d e l i n e a r em in im a l . A p ar t f r o m th e g en e r a l d i ff i cu l ti e s o f i d en t i f y in gg l o b a l r e q u i r e m e n t s , t h e r e s h o u l d b e n o s i g n i f i c a n tp r o b l e m s i n a p p l y i n g t h i s g u i d e l i n e .


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Identify Volatile Requirements 249

Key benefitCosts of introductionCosts o f applicationGuidel ine type

Simplif ies requirementschange managementLowLowAdvanced

Y o u s h o u l d m a i n t a i n a li s t o f t h e m o s t v o l a ti l e r e q u ir e -m e n t s , t h a t i s , t h o s e r e q u i r e m e n t s w h i c h a r e m o s t l i k e l yto ch an g e . I f p o s s ib l e , y o u s h o u ld p r e d ic t l i k e ly ch an g e st o t h e s e r e q u i r e m e n t s .

Benefits S y s t e m d e v e l o p e r s m a y b e ab le t o d e s i g n t h e s y s te m s ot h a t v o l a t i l e r e q u i r e m e n t s a r e i m p l e m e n t e d i n m o d u l e s

w h i c h a r e lo o s e l y c o u p l e d t o t h e r e s t of t h e s y s t em . T h i sm e a n s t h a t s o f t w a r e c h a n g e s t o a c c o m m o d a t e r e q u i r e -m e n t s c h a n g e w i l l b e e a s i e r t o i m p l e m e n t . P l a n n in g f or ch an g e i s eas ie r if l i k e ly ch an g es a r ep r e d i c t e d . Y o u w i l l f i n d i t e a s i e r t o m a n a g e t h e e v o l u t i o no f t h e r e q u i r e m e n t s d o c u m e n t a n d t o p la n t h e d e v e l o p -

m e n t o f t h e s y s te m .Implementa t ion

A l l s y s t e m r e q u i r e m e n t s m a y c h a n g e b u t i t i s g e n e r a l l yt h e c a s e t h a t s o m e r e q u i r e m e n t s c h a n g e m o r e f r e q u e n t l yt h a n o t h e r , m o r e s t a b l e , r e q u i r e m e n t s . T o i m p l e m e n t t h i sg u i d e l i n e , e x p e r i e n c e d r e q u i r e m e n t s e n g i n e e r s s h o u l de x a m i n e a l l of t h e s y s t e m r e q u i r e m e n t s a n d i d e n t i f y t h o s ew h i c h a r e l i k e l y t o b e p a r t i c u l a r l y v o l a t i l e . W e r e c o m -m e n d t h a t y o u s h o u l d i d e n t i f y t h e s e r e q u i r e m e n t s d u r i n gt h e r e q u i r e m e n t s v a l i d a t i o n p r o c e s s o r w h e n y o u r i n i t i a ls e t o f t r acea b i l i t y i n f o r m a t io n i s c rea t ed .W e h a v e s u g g e s t e d t h a t t h i s g u i d e l i n e i s a n a d v a n c e dg u i d e l i n e b e c a u s e y o u w i l l n o t r e a l l y g e t a n y b e n e f i t s


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250 Requirements Ma nage m entf r o m i t u n t i l y o u h a v e r e q u i r e m e n t s m a n a g e m e n t a n dc h a n g e m a n a g e m e n t p o l i c i e s i n p l a c e .T h e r e a re d i f fe r e n t t y p e s o f v o l a t il e r e q u i r e m e n t s .

1 M u t a b l e r e q u i r e m e n t s. T h e s e a r e r e q u i r e m e n t s w h i c hc h a n g e b e c a u s e o f c h a n g e s to t h e e n v i r o n m e n t i n w h i c ht h e s y s t e m i s o p e r a t i n g . F o r e x a m p l e , t h e r e q u i r e m e n t s f o ra s y s t e m w h i c h c o m p u t e s t a x d e d u c t i o n s e v o l v e a s t h et a x l a w s a r e c h a n g e d .2 E m e r g e n t r e q u i r e m e n t s. T h e s e a r e r e q u i r e m e n t s w h i c hc a n n o t b e c o m p l e t e l y d e f i n e d w h e n t h e s y s t e m i s s p e c i -f i e d b u t w h i c h e m e r g e a s t h e s y s t e m i s d e s i g n e d a n d

i m p l e m e n t e d . F o r e x a m p l e , i t m a y n o t b e p o s s i b l e t o s p e -c if y, i n a d v a n c e , t h e d e t a i l s o f h o w i n f o r m a t i o n s h o u l d b ep r e s e n t e d . A s st a k e h o l d e r s s e e e x a m p l e s o f p o s s i b l e p r e -s e n t a ti o n s , t h e y m a y t h i n k o f n e w p r e s e n t a t i o n s t h a tw o u l d b e u s e f u l t o t h e m .3 C o n s e q u e n t i a l r e q u i r e me n t s . T h e s e a r e r e q u i r e m e n t sw h i c h a r e b a s e d o n a s s u m p t i o n s o n h o w t h e s y s t e m w i l lb e u s e d . W h e n t h e s y s t e m i s p u t i n t o u s e , y o u w i l l f i n d

t h a t s o m e o f t h e s e a s s u m p t i o n s w i l l b e w r o n g . Y o u w i l la l s o f i n d t h a t u s e r s w i l l a d a p t t o t h e s y s t e m a n d f i n d n e ww a y s t o u s e i t s f u n c t i o n a l i t y . T h i s w i l l r e s u l t i n d e m a n d sf r o m u s e r s f o r s y s t e m c h a n g e s a n d m o d i f i c a t i o n s .4 C o m p a t i b i l i t y r e q u i r e m e n t s . T h e s e a r e r e q u i r e m e n t sw h i c h d e p e n d o n o t h e r e q u i p m e n t o r p r o c e s s e s . A s t h e s ec h a n g e , t h e s e r e q u i r e m e n t s a l s o e v o l v e . F o r e x a m p l e , a ni n s t r u m e n t c o n t r o l s y s t e m m a y h a v e t o b e m o d i f i e d w h e n

a n e w d i s p l a y i s a d d e d .T o i d e n t i f y v o l a t i l e r e q u i r e m e n t s , y o u m u s t i n v o l v e a p p l i -c a t i o n d o m a i n s p e c i a l i s t s w h o w i l l k n o w w h i c h d o m a i ni n fo r m a t i on is fa i r ly s t a b l e a nd w hi c h i s va r i a b l e . I f yo uc a n a s s i g n r e q u i r e m e n t s t o o n e o f t h e a b o v e c l a ss e s , t h a ti s a l s o a n i n d i c a t o r o f vo l a t i li t y . I t m a y a l s o be h e l p fu l t od i s c u s s p o s s i b l e o r g a n i s a t i o n a l c h a n g e w i t h s e n i o rm a n a g e m e n t . H o w e v e r , t h e y m a y

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