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Software Engineering

Topic 4:

Software Specification

Yor !a"e: #####################

Co"pter Science $ Engineering Depart"ent

The Chinese University of %ong &ong

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Prelude on Specification

♦ ( specification is a precise state"ent of there)ire"ents that a syste" "st satisfy

♦the ter" *specification+ is se at ifferent

stages of syste" eveop"enti re)ire"ent specification

ii esign specification

iii "oe specification

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Specification

♦ ( roa ter" that "eans _____________♦Use at ifferent stages of software

eveop"ent for ifferent prposes

♦2eneray, a state"ent of agree"ent _____________ etween 3 procer an cons"er of a service

3 i"pe"enter an ser

♦ ( esirae )aities "st e specifie

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What Is A Specification?

♦ ( specification at so"e eve states there)ire"ents for the i"pe"entation at aower eve

♦t is viewe as a efinition of ######## thei"pe"entation "st provie, not #########

♦The istinction etween *what+ an *how+ isnot sharp.

e.g., a si"pe way to escrie *what+ is 5st to givean e6a"pe of *how+e.g., display of time: “hour” + “:” + “minute” 1 ≤ 2 digit ≤ 12 0 ≤ 2 digit ≤ 59

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Uses of Specification

♦ State"ent of ############## re)ire"ents 3 "a5or faires occr ecase of "isnerstanings

etween the procer an the ser

3 ( sers8 nees are so"eti"es not ceary nerstoo

y the eveoper 3 So"eti"es, even the ser has no cear iea of what

e6acty the esire proct is

3 9The harest singe part of iing a software syste"

is eciing precisey what to i9 . ;roo

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Uses of Specification (cont.)

♦State"ent of the interface etween the ######### an the controe ############

3 serios nesirae effects can rest e to

"isnerstanings etween software engineers

an o"ain e6perts aot the pheno"ena

affecting the contro fnction to e i"pe"ente y

software

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♦State"ent of re)ire"ents for ############ 3 esign process is a chain of specification i.e.,

efinition–i"pe"entation–verification steps

?requirements specification refers to efinitionof ############## ehavior esign specification "st e verifie against it

?design specification refers to efinition of the

################software architectre coe "st e verifie against it

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♦ ( reference point ring ############ 3 corrective "aintenance ony changes

i"pe"entation or esign

3 aaptive an perfective "aintenanceoccr ecase of re)ire"ents changes

?re)ire"ents specification "st change

accoringy

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Specification Qualities

1 Spec sho e cear, na"igos, annerstanae

3 pictres are etter, if possie e.g. 2aieo

3infor"a spec, written in natra angagesEngish, are i

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Spec Exaples

i ( select co""an in a wor processor 3 Seecting is the process for esignating areas

of yor oc"ent that yo want to wor< on.

Bost eiting an for"atting actions re)ire

two steps: first yo seect what yo want towor< on, sch as te6t or graphicsF then yo

initiate the appropriate action.

!!!!!!!!!!!

!!!!!!!!!!!

not sure if

possi"le or not

fro the spec

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Spec Exaples

ii ( "ission-critica pro5ect 3 The "essage "st e tripicate. The three

copies "st e forware throgh three

ifferent physica channes. The receiver

accepts the "essage on the asis of a two-

ot-of-three voting poicy.

When? As soon as two identical essagesare recei#ed or has to wait for $

essages?

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' Spec sho e ################ 3 (n e6a"pe: wor processing for *te6t+

? Engish spec:

? The whoe te6t sho e

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0 Spec sho e ######################## 3 internay co"pete sef-containe

? efine a new concept or ter"inoogy it ses

? gossary hepf for this prpose

3 e6ternay co"pete: co"pete with respect to serre)ire"ents

? specify a the fnctiona re)ire"ents

? e wary of non-fnctiona re)ire"ents e.g., perfor"ance,

e6ceptiona cases

? ifficty: when sho one stopDe to the ifficties in achieving co"pete spec, the se of

the ################ principe is especiay i"portant

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4 Spec sho e ################## 3 Geferring to the specification process

? start fro" a s

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%lassification of Specification St&les

1 or"a vs. nfor"a spec 3 infor"a - natra angage strctre or non-

strctre

?e.g. given earier in this ectre

3 for"a - a fy precise synta6 an se"antics

3 se"i-for"a - notation withot a co"peteyprecise se"antics

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' Hperationa vs. Descriptive spec 3 Hperationa - escrie the intene syste" y

escriing the esire ehavior, say throgh a"oe of the syste"

3 Descriptive - state the esire-properties of the syste"in a prey ecarative fashion

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3 e6a"pes of operationa spec aot eipse? operationa:

? escriptive:

3 e6a"pes of operationa spec aot sorting an array

? operationa:? escriptive:

3 escriptive specs ten to e "ore astract than

operation specs ecase they o not ias the reaer

towars any particar i"pe"entation 3 the istinction etween operationa an escriptive

specs is not sharp

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Spec St&le Exaples

1 (n operationa spec for eipse 3 E is the path of the point that "oves so that the s" of its istances

fro" two fi6e points P 1 and P 2 is ###########, an ###########.

3 Iroperty of operationa spec:

###############

p' p

a "

ap' ap * "p' "p

(x+ &)

x

&

( escriptive spec: _______________ where the center of the ellipse is (,+,) and

a+ b+ and c are suita"le constants.

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Spec St&le Exaples

() specs a"out sorting - perational spec/

0 1et a "e an arra& of n eleents. 2he result of sorting a is an arra& b of n eleents such that the first eleents of b is the iniu of a (if se#eral eleents of a ha#e the sae #alue+ an& one of the is

accepta"le)+ the second eleent of b is the iniu of the arra& ofn-1 eleents o"tained fro a "& reo#ing its iniu eleent3and so on until all n eleents of a ha#e "een reo#ed.

0 4eature/ !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

- 5escripti#e spec/

0 2he result of sorting a is an arra& b which is a perutation of a andis sorted.

0 4eature/ !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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0 Data paraig" vs. Irocess paraig" 3 ata paraig" - the spec avocates the pri"acy of ata

astractions? DD ata fow iagra"s

3 process paraig" - the spec focses on se)ences of

events or actions operations? SB inite State Bachine

? Ietri !et

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6erification of Specs

♦ specs "st e verifie prior to esign an i"pe"entation♦ two genera techni)es:1 oserve the yna"ic ehavior of the specifie syste" to chec< its

correctness ################### spec

' anayJe the properties of the specifie syste" that can e ecefro" the spec ##################### spec

♦ effectiveness of oth techni)es increases when for"aity of specincreases.

♦ Techni)e 1 co e one via si"ation, yieing prototype of thespecifie syste"Techni)e ' co e one y h"an inspection or theore"proving

♦ Kerifying spec correctness, consistency an co"peteness isfor"iae an teios tas

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perational Specifications

( Data ow Diagra"s DD

; inite State Bachines SB

C Ietri !ets I!

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A) 5ata 4low 5iagras

They escrie syste"s as coections of atathat are "anipate y fnctions.

3 ;asic ee"ents

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♦e.g.+ 545 for (a") 7 (ca7d) 3 igre 4.1

3 igre 4.': ( si"pifie infor"ation syste" for a

pic irary a first appro6i"ation of the syste"

3 igre 4.0: ( finer escription partia refine"ent

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A) 5ata 4low 5iagras/ A Siple Exaple

specifes evaluation o

(a + b) * (c + a * d)

4igure 8.'

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© Chinese University, CSE Dept. Software Engineering / 4 - '=

A %onstruction 9:ethod; (')

......

Input'

Input(

Inputn

.utput

'

.utput(

.utput

n orat on

s&ste

1. Start rom the “context” diaram

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A %onstruction 9:ethod; ()

A

A'

A$

A(

A8

A<

A=

A>

?'

?(

?$ ?8

Ag

I.

I

.

@

B

:

C

P Q

D

S

2

'

(

$

8

:

C

!. "roceed b# refnements until #ou reach“elementar#” unctions (preserve balancin)

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5ata 4low 5iagras/ A 1i"rar& Exaple

Shel#es

1ist of Authors

1ist of titles

1ist of topics

2itle and author

of reuested "ooF3 nae

of the user

Get a "ooF

?ooF

1ist of "ooFs "orrowed

?ooF title3

user nae

2opic reuest

"& the user

Search "&

topics

?ooF reuest

"& the user

?ooF

reception

2opic1ist of titlesreferring to the topic

?ooF

Author

2itle

5ispla& of

the list of titles

2opic

2itle

4igure 8.

fi f F

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Defineent of 9Get a ooF;

She-ves

List of (thors

List of tit-es

Ti t-e an athor

of re)este 1oo

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♦ Drawac< of the irary spec1 The se"antics of the sy"os "ight nee frther

e6panation.? e.g., *fin oo< position+

? !ee oth *athor+ an *tite+ or one is enogh

' Contro aspects are not efine y the "oe

i reations of otpt are nspecifiee.g. igre 4.4

ii synchroniJation etween syste" co"ponents is nspecifiee.g. igre 4.7

♦ n s""ary, DD is an attractive graphica notation, t it sti

ac

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$

%

&

'

utputs rom $, ', % are all needed-

utputs or & and are

produced at the same time-

4igure 8.8

A) 5 4l 5i

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♦Contro infor"ation is asent

'$

"ossible interpretations(a) $ produces datum, /aits until ' consumes it(b)$ and ' are autonomous activities that have di0erent s

(b1) ' can read the datum rom $ and consume it(b!) a pipe is inserted bet/een $ and '

4igure 8.<

A) 5 t 4l 5i

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♦ To overco"e the DD rawac

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d'

d

dn

H

Σ

2rigger

4igure 8.= A partial 545 augented with control flow arrows. 2he trigger is a control flow arrow. It is dashed rather than continuous. 2he

function 9su; associated with the "u""le is applied to all data

existing in the "oxes as soon as a trigger occurs.

U:1 U 5i

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U:1 Usecase 5iagras

♦UBL: Unifie Boeing Langage♦Use-case iagra"s efine fnctions on asis

of actors an actions

"orrow "ooF

return

book

li"rar&

update

li"rarian

custoer

U:1 A ti it 5i

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U:1 Acti#it& 5iagras

♦ (ctivity iagra"s representwor

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U:1 Seuence 5iagras

♦Descrie how o5ects interact y e6changing"essages

♦Irovie a yna"ic view 1i"rarian %atalogue

member card +

"ooF reEuest membership

.A

book request

book available

book borrowed

time

%ustoer

U:1 %olla"oration 5iagras

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U:1 %olla"oration 5iagras

♦2ive o5ect interactions an their orer ♦E)ivaent to se)ence iagra"s

%ustoer 1i"rarian %atalogue

'/ e"er card )

"ooF reEuest

(/ e"ership .A

$/ "ooF reEuest

8/ "ooF a#aila"le

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) ( )

%ontrol 4low

♦e nee to escrie contro aspects of a syste"in orer to "a

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) 4inite State :achines (4S:s)

3 E6a"pes? igre 4.>, igre 4.@? igre 4.A

? igre 4.1 a refine poicy

3 State transition "atri6: a "atri6 to enote the transition

fnction Je.g. 2iven an SB of n states q1 .. qn

......

i....

....

......

= ..

....

..

n

'

n'

..q

q j

q

q

qqk qq

δ outgoing arcs

incoing arcs

M F i

iff J(s M+ i) * sF


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a a

b

bc

q

q

q

q

1

20

3

On Off

Push switch

Push switch

4igure 8.>

4igure 8.N

Hn Hff

%igh-pressre aar"

%igh-te"peratre aar"

Gestart

4igure 8.O


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Iressre signa Te"peratre signa

Sccessf

recovery

Unsccessf

recovery

OffNormal

Pressureaction

Hff !or"a

Iressreaction

Te"peratre signa

Te"peratreaction

Sccessf

recoveryUnsccessf

recovery

Iressre signa

4igure 8.',


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♦ SBs to specify sets of acceptae strings 3 ag"ente ter"s1 one initia state, , ∈ Q

' a set of fina states, F , 4 ⊂ Q enote y oe circenoes

0 a finite set of otpts, 4 the transition fnction J is ag"ente to proce otpt

signas

J/ Q K I L Q K


4S:s as Decogniers

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4S:s as Decogniers

q

q q q q

q q

q

b

e g i

n

e

n

d

0

1 2 3 4

5 6

f

qf is a nal state

4igure 8.'' An 4S: accepting the Fe&words ________ and _________

4S:s as Decogni ers

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4S:s as Decogniers

_

q q

Legend: is an abbreviation for a set of arrows

labeled a, b,..., z, A,..., Z,

is an abbreviation for a set of arrowslabeled 0, 1,..., 9, respectively

0 1 2

4igure 8.' An 4S: accepting the

identifiers of a prograing language


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♦ S""ary aot SBs

3 avantages:

1 si"pe

' wiey se especia in co"pier, I.L., (

3 isavantages:1 its co"ptationa power is i"ite e to finite "e"ory. e.g.,har to ea with rea n"ers whose possie vaes are infinite.

' n"er of states "ay e e6posive P: %ow "any states are neee to escrie a 4-yte ong register (: #################ifferent statesQ

0 SBs are essentiay a synchronos "oe - inappropriate forconcrrent an asynchronos co"ponents in a syste".



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3 i"prove"ents:1 escrie an appro6i"ation to the syste"

withot too "ch etais

' "oify an change the SB "oe

0 enrich the "oe y new featres e.g., a

"ore co"pe6 preicates for state transitions

) 4S:s/ State Explosion Pro"le

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) p

♦E6a"pe: 3 ( procer process -

?proces "essages an pts writes the" into a ffer

3 ( cons"er process -

? reas an re"oves the "essages, an cons"e the"

3 ( ffer -?a two-sot ffer to store "essages

igre 4.10: three co"ponents igre 4.14: escrie the whoe syste"

? %ow "any states are there


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Producer

p1

c2

Buffer

1

produce

write

read

consume

write

read read

write

p2

Consumer

c1

20

4igure 8.'$


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essage in "uffer producers state consuers state

consume

proce

cons"e

proce

consume

proce

consume

proce

proce proce

cons"e cons"e

write

rea

write

rea

rea

write

rea

write

1

12

1

' '

M1, p ,c O

M, p ,c O

1 1

M1, p ,cO

M1, p ,c O

M1, p ,c O

' 1

1 '

1

'

' ' M', p ,c O ' '

M', p ,c O 1 '

M', p ,c O ' 1

11

4igure 8. '8


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) p

3 f we have n ifferent ssyste"s, each one with &i states,the resting syste" has a carinaity of

############ ############### state e6posion

3 igre 4.17 shows i"prove"ents over igre 4.14 yStatecharts with (!D parae eco"position.

? P: %ow "any states carinaity are there

? (: ############# ############ state increase

) 4S:s with Parallel 5ecoposition

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) S s w a a e eco pos o

Idle

%oncurrentWorF

P'

P

produce

write

%'

%

read

consue

'

,

write

write

read

read

start stop

%onsuerProducer uffer

4igure 8.'< Statecharts with AC5 parallel decoposition.

%) Petri Cets/Specif&ing As&nchronous S&stes

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Specif&ing As&nchronous S&stes

♦ RIetri 1A=' C.(. Ietri Ih.D Dissertation U of ;onn.

♦ ;asic ee"ents1 a finite set of paces circes

' a finite set of transitions ars

0 a finite set of arrows connecting paces an transitions with a weightinteger if necessary

%) Petri Cets

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%) Petri Cets

4igure. 8.'=

%) Petri Cets

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( )arpe I,T,,I: paces T: transitions I, T are finite

: fow reation F⊆ {P×T}∪ {T×P}: weight fnction W: F N – {0}Iroperties:

1 I ∩ T ' I ∪ T ≠ 0 ⊆ I × T ∪ T × I

4 : → !-VW

Defat vae of is 1

State efine y "ar

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♦ Hperation of a Ietri !et I!1 state: a I! is given a state y "ar

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> fire: the n"er of *inpt weight+ to

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4igure. 8.'=(a)(d)

%) Petri Cets

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1'starvation: a process that never receivesaccess to a neee resorce.

? Starvation "ay happen e to *##############+

? It two to

%) Petri Cets

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4igure 8.'=(a) with a different arFing

%) Petri Cets

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4igure. 8.'>A Petri net that can enter a deadlocF state

%) Petri Cets

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10eaoc

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4igure. 8.'N

A odification of the Petri net of 4igure 8.'> that is li#e.

4igure. 8.'O

A Petri net with partial star#ation.

%) Petri Cets/ Producer%onsuer Exaple

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I I

write

proce

C

C

cons"e

1 '

rea rea

write write

rea

1

1

'

'

C1C'

cons"e

1 '

rea

writewrite

rea

I1 I'proce

integration

4igure. 8.,

%) Petri Cets/ Producer%onsuer peration

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4igure. 8.'

An integrated Petri net descri"ing

a producerconsuer s&ste.

%) Petri Cets

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♦ avantages over SB:1 graphica co"pe6ity - state space of the

co"ponents is ony aitive, not "tipicative

3 Ba5or rection of "oe co"pe6ity

' the concrrency of inepenent activities is

escrie propery y a ############### .

3 E.g. Mproce, write, proce, rea, cons"e,

write, rea, cons"eO

%) Petri Cets

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P: "oify it so that fferis 0.

4igure. 8.'

An integrated Petri net descri"ing

a producerconsuer s&ste.

%) Petri Cets

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' !ees techni)es to prevent starvation.

2eneray, it is not possie to specify a seection

poicy etween ifferent enae transitions.0 ############# isses are not we "oee

%hannel '(for correct

essage)

%hannel (for incorrect

essage)

♦ I! i"itations1 I! to

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P P

P

P P

t t

t t

P P

t t

1

1 2

3

4

5

6

7

4

2

3

6

5

%) Petri Cets

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♦I! e6tensions1 assign vaes to to

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0 ti"e Ietri nets in which a pair Mt"in,t"a6O is

associate with each transition.

tin * '

tax * 8

priorit& * ' (low)

tin *

tax * $

priorit& * $ (high)

*R t' cannot fire "etween ≤ t ≤ $

t' t

p' p p$

(n earier e6a"pe

? ( "ore precise spec y choosing igre 4.'0 or igre 4.'4

Original message

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Message triplication

Message copies

Message copies transmission

tmin =tmax =

tmin =tmax =

tmin =tmax = 0

0

for all three transitions

PC1

PC2

PC3

c1k1

c2k2

Forwarded message

tvoting1 tvoting2 tvoting3

{

{

{

4igure 8.$

Original message

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Message triplication

Message copies

Message copies transmission

tmin =

tmax =

tmin =tmax =

tmin = 0tmax = 0

PC1

PC2

PC3

c1

k1

c2k2

tvoting

Forwarded message

4igure 8.8

5escripti#e Specifications

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Descrie the esire ######### of a syste" rather

than the esire ###########

( Entity-Geationship Diagra"s

3 ####################

; Logic Specifications 3 ####################

C (geraic Specifications s

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♦ ;asic ee"ents

1 entities - coections of ite"s that share co""on properties.

' reations - connections etween two entities.

0 attrites - characteristics within each entity.

( reation R on two entities A, is a set of pairs Ma, "O,

where !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

(A) Entit&Delationship (ED) 5iagras

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!!!!!!!!!!!Finds of constraints on the relationship R

S2U5EC2

%1ASS

ECD.11E5!IC

CA: E

SE

AGE

SU?BE%2

%.UDSE!I5

:A!ECD.11:EC

4igure 8.< An ED diagra descri"ing

a relationship "etween students and

classes


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© Chinese University, CSE Dept. Software Engineering / 4 - >>

( G ;

( G ;

( G ;

( G ;

♦Geations can e partia

♦They can e annotate to efine

3 one to one

3 one to "any

3 "any to one

3 "any to "any

Con inar& Delations

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© Chinese University, CSE Dept. Software Engineering / 4 - >@

5irector

ProMect

Eplo&ee

5epartent

AssignedParticipate

@ead.f

5ata 5uration


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© Chinese University, CSE Dept. Software Engineering / 4 - >A

♦ S""ary aot EG iagra"s:1 EG iagra"s are a se"ifor"a spec notation.

' De to the ac< of e6pressive power in EG iagra"s,

we nee to a properties as infor"a co""ents.

e.g. co"ine with *ogic specification+ to e shown ater

0 EG iagra"s are a escriptive notation ecase they

state the entities an their properties.

? iey se in ataase appications for a nifie view of

ata. P: what are the "a5or ataase "oes

() 1ogic Specifications

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© Chinese University, CSE Dept. Software Engineering / 4 - @

♦ hat is ogic spec

1 ;ase on first-orer theory HT - an e6pression for"a invoving

sy"os in traitiona "athe"atics.

' Logica connectives - an, or, not, i"pies, an ≡ ogica e)ivaence- are se.

0 the type of rest "st e ;ooean.

4 se )antifiers e.g., *e6ists+ ∃, *for a+ ∀. ⇒ )ic< e6a"pes

♦ a variae that occrs in a for"a is free if it is not )antifie.♦ a )antifie variae is on.

♦ if a variaes in a for"a are )antifie, the for"a is cose.

♦ a cose for"a is aways either tre or fase.@ow to o"tain?

♦ the cosre of a for"a is otaine y )antifying a of its free variaes

with the ############ )antifier.


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© Chinese University, CSE Dept. Software Engineering / 4 - @1

'. x R & and & R implies x R 3

. x * & ≡ & * x3$. for all x+ &+ (x R & and & R implies x R )3

8. x ' T x − '3

. for all x (x ≥ ') or (x ≤ −') or (x * ,)

>: tre or fase

Tre if x is #########F fase if x is ###########

Co"ine with EG iagra"s: See the igre in ne6t page.

CA: E

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*( cass can e6ist ony if then"er of enroe stents isgreater than five, an then"er cannot e6cee thevae B(#E!GHLLBE!T+

∀ in CL(SS

7 ≤ carinaity V a Z Ma,O inE!GHLLED#! W

≤ .B(#E!GHLLBE!T

a: stent : cass

S2U5EC2

%1ASS

ECD.11E5!IC

CA: E

SE

AGE

SU?BE%2

%.UDSE!I5

:A!ECD.11:EC


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♦ Specifying co"pete progra"s:

inpt-otpt assertions5efinition/

1et P "e a seuential progra+ letTi'+ i+ H+ inR denote the seuence

of Ps input #alues and To'+o+

H+oR the seuence of Ps output

#alues

A propert&+ or reuireent+ for P isexpressed as

Pre (i'+i+H+in)V

P (!!!!!!!!!!!!!!)

Post(o'+o+H+o+i'+i+H+in)V

where Pre (i'+i

+H+i

n) denotes a 42

forula ha#ing i'+i+H+in as free #aria"lesand Post(o

'+o

+H+o

+i

'+i

+H+i

n)

denotes a

42 forula ha#ing o'+o

+H+o

and+

possi"l&+ i'+i

+H+i

n as free #aria"les.

Pre !!!!!!!!!!!!!!!!!! of P

Post !!!!!!!!!!!!!!!!! of P

Cote/ e#en siple spec pro"les a&reuire an& details and a& "e hard tounderstand

1ogic Specifications for %oplete Progras

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npt-otpt assertions ass"ing integers in the foowing'. exists ( i' * × i( ) V

P

o' * i' i( V

. i' R i( VP

i' * i( × o' o( and o( ≥ , and o( T i( V

$. trueV

P (o * i' or o * i() and o ≥ i' and o ≥ i( V

no constraint on input


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8. i' R , and i

R , V

"

(e!ists '+

(i

' * o ×

' and i

* o ×

))

and not

(e!ists h (e!ists '+

(i

' * h ×

' and i

* h ×

) and h R o))V

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© Chinese University, CSE Dept. Software Engineering / 4 - @=

Exaple/

input!word(+n) ≡ (for all i ( ≤ i ≤ n) implies alpha"etic(ci))

input!text(+n) ≡ ( i * YZ and in * YZ and

( e!ists F (for all M ('≤ M ≤ F) implies( e!ists h M+ M (input!word( M+ M h M) and

' * ' and F hF ' * n and

(' ≤ M T F) implies ( M)' * M h M and

i M)h M)' * Q Q ) ) ) ) ) )

ci is an alpha"etic character

h M / [length of Mth word\ '

M / starting position of Mth word

⇒ M h M / ending position of Mth word

F/ no. of words

n/ last word ends at

position F hF '/ first word start

fro position '

M'th

word starts fro the ending position of Mth word plus (' for space

charactor at position M h M ')


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© Chinese University, CSE Dept. Software Engineering / 4 - @>

inpt#te6t",n

Nwe#sha#overco"eN

< ####

"1 #### "' #### "0 ####

h1 #### h' #### h0 ####

"1[h1 #### "'[h' #### "0[h0 ####

⇒ specifying a co"pete progra" )ic

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© Chinese University, CSE Dept. Software Engineering / 4 - @@

nter"eiate assertions: aow e6pressions in pre- an post-conitions

assertions to refer to progra" variaes

>. n R , V - n is a constant #alue

pro#edure search(ta"le/ in integer!arra&3 n/ in integer3 eleent/ in integer3found/ out oolean)3

found ≡ (e!ists i ('≤ i ≤ n and ta"le(i) * eleent)) V

N. n R , V

pro#edure re#erse(a/ in out integer!arra&3 n/ in integer)3

for all i (' ≤ i ≤ n) implies (a(i) * old !a(ni')) V

O. n R , Vpro#edure sort(a/ in out integer!arra&3 n/ in integer)3

sorted(a+ n) V+

sorted(a+n) ≡ (for all i ('≤ i T n) implies a(i) ≤ a(i'))

1ogic Specification for Specif&ing %lasses

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© Chinese University, CSE Dept. Software Engineering / 4 - @A

♦ nvariant preicates an pre/post conitionsfor each "etho

♦E6a"pe of invariant specifying an arrayBIL i"pe"enting the astract ata type

SETfor all i, j (1 ≤ i ≤ length and 1 ≤ j ≤ length and i≠ j)implies 2"34i5≠2"34 j5

2"3 arra# o si6e length

(assure no 7777777777777 are stored)

1ogic Specification for Specif&ing Conterinating eha#iors

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♦ E6a"pe of non-ter"inating syste"s

###############

♦ E6a"pe: procer [ cons"er [ ffer ♦

nvariant specifies that whatever has eenproce is the concatenation of what has eenta

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© Chinese University, CSE Dept. Software Engineering / 4 - A1

3 The principe of separation of concerns for spec:

Separate fnctiona specs fro" perfor"ance specs,fro" ser interface specs, etc.

3 non-fnctiona spec

? the attrite of a syste" which cannot e provie y

########################## 3 Separation of concerns "ay rest in sing ifferent

notations for specifying ifferent aspects of a syste"

? E.g., ( oc"ent proction syste" with two views 3

? DD: shows ata epenencies? SB: specifies orer of e6ections

5ata 4low 6iew (')

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© Chinese University, CSE Dept. Software Engineering / 4 - A'

User

Formattingoptions

PredefinedText skeletons

Customers

Customer data(name, type ofdocument)

PrintDocument

PredefinedFormats

Documentproduction

5ocuent Production Exaple/

%ontrol 4low 6iew ()

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Search inCustomers

Get user name

Get other data fromthe data base

Get other relevant datafrom user interaction

Get appropriate textskeletons frompredefined text library

Print document

Compose the document by choosingformatting options(this involves interaction with the user andaccess to the Formats data base)

(b)

uilding and Using Specifications in Practice

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3 The principe of incre"entaity is no ess i"portant to

spec than to i"pe"entation. ncre"entaity sho eappie in the constrction of spec to the eve of rigoran for"aity.

3 ( spec oc"ent is say a "i6tre of infor"anatra angage sentences, se"ifor"a, figres, an

fy for"aiJe "oes. 3 P: Can we hope for one niversa spec angage

3 (: #######Q Spec angages are harer, "oreco"pe6 than progra""ing angages. e cannot

e6pect there wi e ony one niversa spec angageQ 3 The se of ######## is very i"portant

Specifications for the EndUser

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♦Gigoros specs sho e se as co""onreference for procer an ser

♦They hep re"oving a"igity,inco"peteness, X

♦Can specs e nerstoo y en-ser 3 They can e the starting point for a ##########

3 They can spport so"e for" of ani"ation e.g.,

see Ietri nets

2opic 8 %onclusion (')

♦ Specifications escrie

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♦ Specifications escrie

3 what the sers nee fro" a syste" re)ire"entsspecification

3 the esign of a software syste" esign an architectrespecification

3 the featres offere y a syste" fnctiona specification

3 the perfor"ance characteristics of a syste" perfor"ancespecification

3 the e6terna ehavior of a "oe "oe interfacespecification

3 the interna strctre of a "oe interna strctraspecification

2opic 8 %onclusion ()

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© Chinese University, CSE Dept. Software Engineering / 4 - A>

♦Descriptions are given via sitae notations 3 There is no *iea+ notation

♦They "st e "oar

♦They spport co""nication an interaction

etween esigners an sers

Documents

3100-topic4 (2)