The

Engi

neer

ing

of S

oftw

are

Bran

Sel

icIB

M S

oftw

are

Gro

up –

Rat

iona

l Sof

twar

ebs

elic

@ca

.ibm

.com

2

A G

reat

Pio

neer

Spe

aks…

♦“I

see

no m

eani

ngfu

l diff

eren

ce b

etw

een

prog

ram

min

g m

etho

dolo

gy a

nd m

athe

mat

ical

met

hodo

logy

”(EW

D

1209

)

Edsg

er W

ybe

Dijk

stra

(193

0 –

2002

)

3

Two

Opi

nion

s“B

ecau

se [p

rogr

ams]

are

put

toge

ther

in th

e co

ntex

t of a

set

of

info

rmat

ion

requ

irem

ents

, the

y ob

serv

e no

nat

ural

lim

itsot

her

than

thos

e im

pose

d by

thos

e re

quire

men

ts. U

nlik

e th

e w

orld

of

engi

neer

ing,

ther

e ar

e no

imm

utab

le la

ws

to v

iola

te.”

-W

ei-L

ung

Wan

gC

omm

. of t

he A

CM

(45,

5)

May

200

2

“All

mac

hine

ry is

der

ived

from

nat

ure,

and

is fo

unde

d on

the

teac

hing

and

inst

ruct

ion

of th

e re

volu

tion

of th

e fir

mam

ent.”

-Vitr

uviu

sO

n Ar

chite

ctur

e,Bo

ok X

1stC

entu

ry B

C

4

Wha

t is

Engi

neer

ing?

♦M

erria

m-W

ebst

er C

olle

giat

e D

ictio

nary

:

engi

neer

ing:

the

appl

icat

ion

of s

cien

ce a

nd m

athe

mat

ics

by w

hich

the

prop

ertie

s of

mat

ter a

nd th

e so

urce

s of

en

ergy

in n

atur

ear

e m

ade

usef

ul to

peo

ple

♦W

hat d

oes

this

hav

e to

do

with

sof

twar

e de

sign

?�

“…no

nat

ural

lim

its…

no im

mut

able

law

s to

vio

late

”

5

Wha

t is

Softw

are

Mad

e of

?

6

Pro

cess

ing

Site

Pro

cess

ing

Site

ob

serv

ero

no

ffo

ffo

n

Sta

te?

“on

”

“on

”

Exhi

bit A

: Tra

nsm

issi

on D

elay

Effe

cts

♦Po

ssib

ility

of o

ut o

f dat

e st

atus

info

rmat

ion

7

clie

ntA

no

tifi

er1

no

tifi

er2

clie

ntB

tim

e

on

on

off

off

Exhi

bit B

: Rel

ativ

istic

Effe

cts

♦R

elat

ivis

tic e

ffect

s:�

diffe

rent

obs

erve

rs s

ee d

iffer

ent e

vent

ord

erin

gs (d

ue to

di

ffere

nt a

nd v

aria

ble

trans

mis

sion

del

ays)

8

Pro

cess

ing

Site

Co

mm

un

icat

ion

s M

ediu

m

Pro

cess

ing

Site

Dist

ribut

ion

Tran

spar

ency

Mec

hani

sms

♦Pl

atfo

rm la

yers

that

mas

k ou

t fai

lure

s fro

m th

e ap

plic

atio

n�

e.g.

, rel

iabl

e R

PC s

ervi

ces,

relo

catio

n tra

nspa

renc

y,…

clie

nt

serv

er

Rel

iab

le

Co

mm

Ser

vice

Rel

iab

le

Co

mm

Ser

vice

9

Impo

ssib

ility

Res

ult N

o.1

It is

not

pos

sibl

e to

gua

rant

ee th

at a

gree

men

t ca

n be

reac

hed

in fi

nite

tim

e ov

er a

n as

ynch

rono

us c

omm

unic

atio

n m

ediu

m, i

f the

m

ediu

m is

loss

y or

one

of t

he d

istri

bute

d si

tes

can

fail

�Fi

sche

r, M

., N

. Lyn

ch, a

nd M

. Pat

erso

n,

“Impo

ssib

ility

of D

istri

bute

d C

onse

nsus

with

One

Fa

ulty

Pro

cess

” Jou

rnal

of t

he A

CM

, (32

, 2) A

pril

1985

.

10

Impo

ssib

ility

Res

ult N

o.2

Even

whe

n co

mm

unic

atio

n is

fully

relia

ble,

it is

no

t pos

sibl

e to

gua

rant

ee c

omm

on k

now

ledg

e if

com

mun

icat

ion

dela

ys a

re u

nbou

nded

�H

alpe

rn, J

.Y, a

nd M

oses

, Y.,

“Kno

wle

dge

and

com

mon

kno

wle

dge

in a

dis

tribu

ted

envi

ronm

ent”

Jour

nal o

f the

AC

M, (

37, 3

) 199

0.

11

Tran

spar

ency

Mec

hani

sms?

♦Al

ldis

tribu

tion

trans

pare

ncy

mec

hani

sms

requ

ire

dist

ribut

ed a

gree

men

t !�

Tran

spar

ency

can

onl

y be

app

roxi

mat

ed

⇒th

e ap

plic

atio

n m

ay s

till h

ave

to d

eal w

ith th

e un

plea

sant

si

de-e

ffect

s of

dis

tribu

tion

�Th

e m

ore

trans

pare

ncy

is d

esire

d th

e hi

gher

the

cost

(tim

e,

reso

urce

s, c

ompl

exity

)

♦Th

e en

d-to

-end

arg

umen

t[Sa

ltzer

et a

l.]:

⇒th

e ov

erhe

ad in

trodu

ced

by tr

ansp

aren

cy m

echa

nism

s m

ay

outw

eigh

any

ben

efits

12

Plat

form

Wha

t Sof

twar

e is

Mad

e of

♦Pl

atfo

rm=

the

com

plet

e te

chno

logi

cal b

ase

(SW

and

HW

) req

uire

d to

ex

ecut

e an

app

licat

ion

♦Th

e pl

atfo

rm is

the

“con

stru

ctio

n m

ater

ial”

of s

oftw

are,

con

veyi

ng it

s ph

ysic

al

char

acte

ristic

s (s

peed

, cap

acity

, etc

.) di

rect

ly to

the

appl

icat

ion

Softw

are

Appl

icat

ion

Ope

ratin

g Sy

stem

Com

putin

g Ha

rdw

are

13

Plat

form

s an

d Ap

plic

atio

ns♦

Q: W

hat e

ffect

sho

uld

a co

mpu

ting

plat

form

hav

e on

an

appl

icat

ion?

♦A:

as

little

as

poss

ible

…bu

t, no

less

!♦

Plat

form

-inde

pend

ent d

esig

n (M

DA)

�Se

para

tion

of c

once

rns

(sim

plifi

es d

esig

n)

�Po

rtabi

lity

♦A

soun

d de

sign

prin

cipl

e th

at is

far t

oo o

ften

mis

inte

rpre

ted

as “p

latfo

rm ig

nora

nce”

14

If Tr

ansp

aren

cy is

an

Idea

lizat

ion…

♦Fa

cts

to p

onde

r:�

In th

e In

tern

et A

ge, m

ost i

nter

estin

g ap

plic

atio

ns w

ill be

dis

tribu

ted

�As

our

dep

ende

nce

on c

ompu

ters

incr

ease

s, th

e ph

ysic

al c

hara

cter

istic

s of

our

sof

twar

e (re

spon

se ti

me,

ava

ilabi

lity)

will

beco

me

muc

h of

a

conc

ern

♦Tr

aditi

onal

Pro

gram

min

g =

Logi

c

♦Ph

ysic

al P

rogr

amm

ing

= Lo

gic

+ Ph

ysic

s�

Like

mor

e tra

ditio

nal e

ngin

eers

, sof

twar

e de

sign

ers

mus

t tak

e in

to

acco

unt t

he c

onst

ruct

ion

mat

eria

l out

of w

hich

the

logi

c is

spu

n

�D

ealin

g w

ith fi

nite

reso

urce

s, fi

nite

del

ays,

fini

te re

liabi

lity.

..

♦“A

llm

achi

nery

is d

eriv

ed fr

om n

atur

e, a

nd is

foun

ded

on th

e te

achi

ng a

nd

inst

ruct

ion

of th

e re

volu

tion

of th

e fir

mam

ent.”

15

Core

Con

cept

s fo

r “Ph

ysic

al”

Prog

ram

min

g

16

Qua

lity

of S

ervi

ce♦

The

phys

ical

cha

ract

eris

tics

of s

oftw

are

can

be s

peci

fied

usin

g th

e ge

nera

l not

ion

of Q

ualit

y of

Ser

vice

(QoS

):

a sp

ecifi

catio

n of

how

wel

l a s

ervi

ce c

an (o

r sho

uld)

be

perfo

rmed

�th

roug

hput

, lat

ency

, cap

acity

, res

pons

e tim

e, a

vaila

bilit

y, s

ecur

ity...

�us

ually

a q

uant

itativ

e m

easu

re

♦Q

oS c

once

rns

have

two

side

s:

�of

fere

d Q

oS:t

he Q

oS th

at is

ava

ilabl

e

�re

quire

d Q

oS:t

he Q

oS th

at is

requ

ired

to d

o a

job

17

Res

ourc

e(e

.g.,

data

bas

e)

Reso

urce

s an

d Q

oS C

ontra

cts

♦R

esou

rce:

an

ele

men

t who

se a

bilit

y or

cap

acity

is li

mite

d, d

irect

ly o

r in

dire

ctly

, by

the

finite

cap

aciti

es o

f the

und

erly

ing

phys

ical

el

emen

ts

♦Th

e re

latio

nshi

p be

twee

n re

sour

ces

and

reso

urce

use

rs

Clie

ntQ

oS C

ontra

ctR

ead

DB

()

Key

issu

e:(R

equi

redQ

oS≤ ≤≤≤

Offe

redQ

oS) ?

Requ

iredQ

oS(e

.g.,

2 m

s re

spon

se)

Rea

dD

B()

Offe

redQ

oS(e

.g.,

1 m

s re

spon

se)

18

QoS

Con

tract

Ver

ifica

tion

♦C

an Q

oS c

ontra

cts

be s

tatic

ally

che

cked

by

a co

mpi

ler?

�Th

e go

od n

ews:

Yes

(in

mos

t cas

es)

�Th

e ba

d ne

ws:

typi

cally

requ

ires

com

plex

ana

lysi

s m

etho

ds

(que

uein

g ne

twor

k an

alys

is, s

ched

ulab

ility

anal

ysis

, etc

.)

♦So

me

issu

es:

�In

mos

t cas

es Q

oS v

erifi

catio

n ca

nnot

be

done

incr

emen

tally

–th

e fu

ll sy

stem

con

text

is re

quire

d

�Ea

ch ty

pe o

f QoS

(e.g

., ba

ndw

idth

, CPU

per

form

ance

) co

mbi

nes

diffe

rent

ly –

no g

ener

al th

eory

for Q

oS a

naly

sis

♦H

owev

er, m

uch

of th

is c

an b

e au

tom

ated

19

Auto

mat

ing

QoS

Ver

ifica

tion

♦Se

amle

ss in

ter-w

orki

ng o

f spe

cial

ized

tool

s ba

sed

on

shar

ed s

tand

ards

Mod

el E

ditin

gT

ool

5

3.1

4

Mod

el A

naly

sis

Too

l

Aut

omat

ical

lyde

rived

ana

lysi

sm

odel

µ µµµ

Res

ults

in s

ourc

em

odel

form

at

2.5

QoS

Spe

cific

atio

ns

20

Offe

red

vs. R

equi

red

QoS

♦Li

ke a

ll gu

aran

tees

, the

offe

red

QoS

is c

ondi

tiona

lon

the

reso

urce

itse

lf ge

tting

wha

t it n

eeds

to d

o its

job

Clie

nt

S1

S1

Res

ou

rceA

S2

S2

Res

ou

rceB

♦Th

is e

xten

ds in

two

dim

ensi

ons:

�th

e pe

erdi

men

sion

�th

e la

yerin

gdi

men

sion

: for

pla

tform

dep

ende

ncie

s

CP

UC

PU

CP

U

CP

U

Phy

sica

l Pro

cess

or

CP

U

Phy

sica

l Pro

cess

or

21

Plat

form

-Aw

are

Plat

form

-Inde

pend

ent D

esig

n

22

Plat

form

Aw

aren

ess

♦Aw

aren

ess

of p

ossi

ble

plat

form

effe

cts

�Pe

rform

ance

, ava

ilabi

lity,

…

�E.

g., c

an tw

o co

mpo

nent

s fa

il in

depe

nden

tly o

f eac

h ot

her?

�E.

g., h

ow re

liabl

e is

the

com

mun

icat

ion

betw

een

two

com

pone

nts?

♦El

imin

ates

the

need

for w

orst

-cas

e as

sum

ptio

ns th

at th

e en

d-to

-end

arg

umen

t im

plie

s

23

Spec

ifyin

g Pl

atfo

rm A

ssum

ptio

ns♦

Dis

tribu

ted

vide

o ap

plic

atio

n

Envi

ronm

ent A

:--

IPC

rate

= …

--C

PU s

peed

= …

--av

aila

bilit

y =

…

Envi

ronm

ent D

:--

thro

ughp

ut =

…--

dela

y =

…--

avai

labi

lity

= …

Envi

ronm

ent C

:--

IPC

rate

= …

--C

PU s

peed

= …

--av

aila

bilit

y =

…

Envi

ronm

ent B

:--

IPC

rate

= …

--C

PU s

peed

= …

--av

aila

bilit

y =

…

vp: V

ideo

Pla

yer

vw :

Vid

eoW

indo

wb

: Bro

wse

r

ws

: Web

Ser

ver

vs: V

ideo

Ser

ver

Qo

S d

om

ain

24

QoS

Dom

ains

♦A

dom

ain

in w

hich

cer

tain

QoS

val

ues

appl

y un

iform

ly:

�C

PU p

erfo

rman

ce

�co

mm

unic

atio

ns c

hara

cter

istic

s (d

elay

, thr

ough

put,

capa

city

)

�fa

ilure

cha

ract

eris

tics

(e.g

., av

aila

bilit

y, re

liabi

lity)

�et

c.

♦Th

e Q

oS v

alue

s of

a d

omai

n ca

n be

com

pare

d ag

ains

t th

ose

of a

ny c

oncr

ete

plat

form

to d

eter

min

e its

sui

tabi

lity

25

Conc

lusi

ons

♦M

ost i

nter

estin

g sy

stem

s of

the

futu

re w

ill be

em

bedd

ed in

the

real

(phy

sica

l) w

orld

�

E.g.

, Int

erne

t-bas

ed s

yste

ms

�Ig

norin

g pl

atfo

rm c

hara

cter

istic

s w

ill le

ad to

sig

nific

ant p

roje

ct fa

ilure

s�

…ye

t, pl

atfo

rm ig

nora

nce

has

been

rais

ed to

the

leve

l of a

des

ign

prin

cipl

e!

♦En

gine

erin

g-or

ient

ed s

oftw

are

deve

lopm

ent i

s ba

sed

on u

se o

f�

Mod

els

and

mod

elin

g te

chni

ques

�Fo

rmal

ana

lysi

s te

chni

ques

�…

incl

udin

g th

e us

e of

qua

ntita

tive

anal

yses

(e.g

., Q

oS-b

ased

met

hods

)

♦Th

ese

deve

lopm

ents

are

the

nece

ssar

y co

nditi

ons

for t

he

fund

amen

tal a

dvan

ce n

eede

d to

impr

ove

the

qual

ity o

f sof

twar

e de

velo

pmen

t