25
Middleware
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
1C
hap
ter
8:
Mid
dle
ware
Mid
dle
war
e
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
2C
hap
ter
8:
Mid
dle
ware
Wh
y M
idd
lew
are?
Adv
anta
ges
of D
istr
ibut
ed S
yste
ms
•E
asy
to a
dd n
ew c
ompo
nent
s
•In
tegr
atio
n of
exi
stin
g so
lutio
ns•
Aut
onom
y of
sin
gle
com
pone
nts
•F
lexi
bilit
y an
d ad
apta
bilit
y
Req
uire
men
ts to
Dis
trib
uted
Sys
tem
s
•O
penn
ess,
inte
grat
ion
•M
odul
aris
atio
n, fe
dera
tions
•S
ecur
ity
•M
anag
eabi
lity,
tran
spar
ency
Pro
blem
s:•
diffe
rent
har
dwar
e•
diffe
rent
ope
ratin
g sy
stem
s•
diffe
rent
pro
gram
min
g la
ngua
ges
SU
N S
ola
ris
Het
erog
enei
ty
Sol
utio
n:
Mid
dle
war
e p
latf
orm
as s
oftw
are
infr
astr
uctu
re fo
r ha
ndlin
g he
tero
gene
ity
Win
dow
s N
T/2
000/
XP
HP
UX
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
3C
hap
ter
8:
Mid
dle
ware
Mid
dle
war
eM
iddl
ewar
e:•
Rea
lisat
ion
of d
istr
ibut
ed a
cces
ses
by s
uita
ble
softw
are
infr
astr
uctu
re•
Hid
ing
the
com
plex
ity o
f the
dis
trib
uted
sys
tem
from
the
prog
ram
mer
•S
uppo
rtin
g th
e in
tera
ctio
n be
twee
n ap
plic
atio
n co
mpo
nent
s w
hich
cou
ld r
un o
n he
tero
gene
ous
syst
ems
•S
epar
atio
n of
inte
rfac
e an
d im
plem
enta
tion
•Is
add
ed to
the
oper
atin
g sy
stem
or
build
upo
n it
to ta
ke o
ver
som
e of
its
task
s
The
mid
dlew
are
is b
uild
upo
n di
ffere
nt
oper
atin
g sy
stem
s, n
etw
orks
, and
co
mm
unic
atio
n pr
otoc
ols
(laye
r 1-
4).
The
app
licat
ions
can
be
prog
ram
med
in
diffe
rent
lang
uage
s.
... a
nd th
e m
iddl
ewar
e re
alis
es th
e co
oper
atio
n be
twee
n th
e so
ftwar
e co
mpo
nent
s.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
4C
hap
ter
8:
Mid
dle
ware
Mid
dle
war
e -
Pri
nci
ple
s
Dis
trib
ute
d f
ile s
yste
ms
•D
istr
ibut
ion
tran
spar
enci
es fo
r fil
es
•P
opul
ar b
ecau
se o
f its
sca
labi
lity
Dis
trib
ute
d d
ocu
men
ts•
Exa
mpl
e W
orld
Wid
e W
eb•
Info
rmat
ion
are
seen
as
docu
men
ts, a
ddre
ssed
by
an U
RL
Rem
ote
Pro
ced
ure
Cal
l (R
PC
)•
Ear
ly m
iddl
ewar
e ap
proa
ch fo
r tr
ansp
aren
cy in
com
mun
icat
ion
Dis
trib
ute
d o
bje
cts
(RM
I)•
Enh
ance
men
ts o
f RP
C to
acc
ess
to r
emot
e ob
ject
s
•O
nly
the
inte
rfac
e ca
n be
see
n fr
om o
utsi
de, t
he im
plem
enta
tion
deta
ils a
re
tran
spar
ent
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
5C
hap
ter
8:
Mid
dle
ware
Mid
dle
war
e
Mid
dlew
are
supp
orts
...•
The
com
mun
icat
ion
betw
een
appl
icat
ion
com
pone
nts
(nor
mal
ly R
PC
-or
RM
I-ba
sed)
•C
onst
ruct
ing
mod
ular
app
licat
ions
•D
ynam
ic b
indi
ng•
Sup
port
ing
serv
ices
, e.g
.�
Nam
ing
�S
ynch
roni
satio
n �
Rep
licat
ion
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
6C
hap
ter
8:
Mid
dle
ware
Exa
mp
les
for
mid
dle
war
e
•D
CO
Mas
Mic
roso
ft's
solu
tion
on d
istr
ibut
ed o
bjec
ts
•G
LOB
Eas
(re
sear
ch)
mid
dlew
are
desi
gned
for
larg
e di
strib
uted
sy
stem
•T
he
Co
mm
on
Ob
ject
Req
ues
t B
roke
r A
rch
itec
ture
(C
OR
BA
)as
a
gene
ral (
indu
stry
def
ined
) w
ay to
sup
port
dis
trib
utio
n in
he
tero
gene
ous
syst
ems
•W
eb S
ervi
ces
as a
n ap
proa
ch in
tegr
ated
with
com
mon
Inte
rnet
pr
otoc
ols
form
ing
a “li
ghtw
eigh
t ver
sion
” of
CO
RB
A
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
7C
hap
ter
8:
Mid
dle
ware
Bas
ic T
echn
ique
in M
icro
soft'
s W
indo
ws:
CO
M(C
ompo
nent
Obj
ect M
odel
)•
Sup
port
s th
e de
velo
pmen
t of c
ompo
nent
s th
at c
an b
e dy
nam
ical
ly a
ctiv
ated
and
in
tera
ct w
ith e
ach
othe
r•
Can
be
used
in e
xecu
tabl
es a
s w
ell a
s in
dyn
amic
link
libr
arie
s•
Was
dev
elop
ed to
sup
port
com
poun
d do
cum
ents
•D
CO
M: '
dist
ribut
ed v
ersi
on' o
f CO
M to
sup
port
act
ivat
ion/
inte
ract
ion
with
co
mpo
nent
s lo
cate
d on
ano
ther
mac
hine
. For
a p
rogr
amm
er, t
he d
istin
ctio
n be
twee
n C
OM
and
DC
OM
is h
idde
n be
hind
inte
rfac
es (
acce
ss tr
ansp
aren
cy)
Dis
trib
ute
d C
om
po
nen
t O
bje
ct M
od
el
(DC
OM
)
Act
iveX
: •
cove
rs th
e ta
sks
of O
LE, t
oget
her
with
new
feat
ures
like
sta
rtin
g va
riant
s, s
crip
ting
supp
ort,
…
OLE
: Obj
ect L
inki
ng a
nd E
mbe
ddin
g.
•S
erve
s fo
r gl
uing
toge
ther
diff
eren
t pa
rts
of c
ompo
und
docu
men
ts
CO
M:
•co
mm
unic
atio
n in
fras
truc
ture
be
twee
n di
ffere
nt o
bjec
ts lo
cate
d on
the
sam
e co
mpu
ter
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
8C
hap
ter
8:
Mid
dle
ware
Ob
ject
Mo
del
•D
CO
M b
ases
on
the
rem
ote
obje
ct m
odel
: obj
ects
can
be
plac
ed in
the
sam
e pr
oces
s as
the
clie
nt, i
n an
othe
r pr
oces
s on
the
sam
e m
achi
ne, o
r in
a p
roce
ss o
n a
rem
ote
mac
hine
•B
asic
con
cept
:
�D
istin
ctio
n be
twee
n in
terf
ace
and
impl
emen
tatio
n�
The
dev
elop
er fi
rst s
peci
fies
an o
bjec
t by
its in
terf
ace
in a
n In
terf
ace
Def
initi
on L
angu
age
(ID
L; M
icro
soft
IDL
= M
IDL)
�A
n ob
ject
sim
ply
is a
n im
plem
enta
tion
of a
n in
terf
ace
�In
terf
ace
mea
ns b
inar
y in
terf
ace:
a ta
ble
of p
oint
ers
to m
etho
ds b
elon
ging
to
an in
terf
ace.
In th
is w
ay, i
nter
face
s ar
e la
ngua
ge-in
depe
nden
t
•E
ach
inte
rfac
e is
ass
igne
d w
ith a
glo
bally
uni
que
Inte
rfac
e Id
entif
ier
(IID
)
•D
CO
M o
bjec
t:�
Inst
ance
of a
cla
ss o
bjec
t, w
hich
rep
rese
nts
an in
terf
ace
�B
y ca
lling
a fu
nctio
n CreateInstance
on a
cla
ss o
bjec
t (id
entif
ied
by a
cla
ss
ID, C
LSID
), a
new
obj
ect w
ith th
is in
terf
ace
is b
uild
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
9C
hap
ter
8:
Mid
dle
ware
Ob
ject
Mo
del
All
obje
cts
impl
emen
t a s
tand
ard
inte
rfac
e: IUnknown
•A
poi
nter
to IUnknown
is p
asse
d ba
ck w
hen
crea
ting
an o
bjec
t
•Im
port
ant m
etho
d in
this
inte
rfac
e: QueryInterface
, whi
ch r
etur
ns a
poi
nter
to
anot
her
inte
rfac
e im
plem
ente
d by
the
obje
ct•
By
this
, a s
tand
ard
met
hod
to g
et a
cces
s to
eac
h ob
ject
's m
etho
ds is
giv
en
create
IUnknown
Reference: IUnknown
QueryInterface(deposit)
Reference: deposit
deposit
withdraw
getBal.
setBal.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
10
Ch
ap
ter
8:
Mid
dle
ware
Ob
ject
Mo
del
All
obje
cts
in D
CO
M a
re tr
ansi
ent
•R
efer
ence
cou
ntin
g is
par
t of IUnknown
•H
avin
g no
mor
e re
fere
nces
, an
obje
ct is
des
troy
ed
An
obje
ct c
an im
plem
ent t
he IDispatch
inte
rfac
e
•D
ynam
ic in
voca
tion
of o
bjec
ts•
An
obje
ct d
oes
not h
ave
to k
now
in a
dvan
ce a
ll in
terf
aces
it w
ill h
ave
to
cont
act i
n its
life
time
•W
hen
an o
bjec
t im
plem
ents
this
inte
rfac
e, c
alls
to it
can
be
cons
truc
ted
at
runt
ime
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
11
Ch
ap
ter
8:
Mid
dle
ware
Ob
ject
Iden
tifi
acti
on
and
Act
ivat
ion
Typ
e lib
rary
: sto
rage
for
inte
rfac
e de
finiti
ons
•A
ssoc
iate
d w
ith a
n ap
plic
atio
n•
Use
d to
figu
re o
ut th
e si
gnat
ure
of a
met
hod
to b
e in
voke
d dy
nam
ical
ly
•U
sed
as a
type
libr
ary
for
supp
ortin
g pr
ogra
m d
evel
oper
s
Reg
istr
y(W
indo
ws
regi
stry
)
•U
sed
to p
rovi
de a
map
ping
from
cla
ss id
entif
iers
to e
xecu
tabl
e co
de.
•In
cas
e of
a r
emot
e in
voca
tion,
the
Ser
vice
Con
trol
Man
ager
(SC
M)
on th
e ta
rget
ho
st is
con
tact
ed b
y a
clie
nt to
acc
ess
the
rem
ote
regi
stry
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
12
Ch
ap
ter
8:
Mid
dle
ware
Co
mm
un
icat
ion
in D
CO
MC
lient
sid
e:•
Clie
nt p
roxy
:pro
vidi
ng th
e ob
ject
's in
terf
ace
and
send
ing
the
requ
est t
o th
eob
ject
•P
roxy
mar
shal
ler:
tran
slat
ing
a re
ques
t int
o a
tran
spor
t for
mat
bef
ore
send
ing
Ser
ver
side
:
•O
bjec
t stu
b: r
ecei
ves
a ca
ll fr
om a
clie
nt p
roxy
and
pas
ses
it on
to th
e ob
ject
•P
roxy
mar
shal
ler:
ext
ract
s a
requ
est f
rom
a r
ecei
ves
mes
sage
Com
mun
icat
ion
at th
e be
ginn
ing
only
was
syn
chro
nous
usi
ng R
PC
Alte
rnat
ives
:
•C
allb
ack
inte
rfac
es
�T
he c
lient
pro
vide
s an
inte
rfac
e w
here
the
serv
er c
an c
all b
ack
afte
r w
orki
ng
on a
req
uest
•A
sync
hron
ous
com
mun
icat
ion
�F
or e
ach
met
hod,
two
met
hods
are
impl
emen
ted:
A s
tart
met
hod
the
clie
nt p
asse
s its
req
uest
toA
fini
shm
etho
d th
e cl
ient
cal
ls to
rea
d th
e re
spon
se o
f the
ser
ver
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
13
Ch
ap
ter
8:
Mid
dle
ware
Eve
nts
Rea
l asy
nchr
onou
s co
mm
unic
atio
n w
ithou
t the
nee
d fo
r bo
th, c
lient
and
obj
ect,
to b
e ac
tive:
usi
ng e
vent
s•
An
even
t is
mod
elle
d as
a m
etho
d ca
ll•
An
even
t cla
ss g
roup
s ev
ents
and
can
be
inst
antia
ted
to e
vent
obj
ects
whi
ch c
an
send
eve
nts
of s
peci
fic ty
pes
•T
o re
gist
er a
n im
plem
enta
tion
for
a m
etho
d so
that
eve
nts
can
bese
nt to
it, a
po
inte
r to
the
corr
espo
ndin
g in
terf
ace
has
to b
e se
nt to
the
even
t sys
tem
•T
he e
vent
sys
tem
can
sto
re e
vent
s to
pas
s th
em o
n to
the
rece
iver
late
r
•S
uppl
ier:
som
eone
who
cre
ates
ev
ents
•C
onsu
mer
: som
eone
who
rec
eive
s ev
ents
•m
_eve
nt: m
etho
d of
an
obje
ct
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
14
Ch
ap
ter
8:
Mid
dle
ware
Pas
sin
g In
terf
ace
Po
inte
rs•
A c
lient
doe
s no
t see
dis
trib
utio
n; th
e in
voca
tion
of r
emot
e ob
ject
s w
ith D
CO
M is
th
e sa
me
as a
n in
voca
tion
of a
loca
l obj
ect w
ith C
OM
•D
iffer
ence
: in
CO
M a
n ob
ject
is r
efer
ence
d by
an
inte
rfac
e po
inte
r, in
DC
OM
a
rem
ote
obje
ct is
ref
eren
ced
by im
plem
entin
g an
inte
rfac
e as
a p
roxy
•P
assi
ng o
n an
obj
ect r
efer
ence
to a
noth
er c
lient
is m
ade
by s
endi
ng it
the
prox
y w
hich
con
tain
s al
l con
nect
ion
info
rmat
ion
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
15
Ch
ap
ter
8:
Mid
dle
ware
Nam
ing
in D
CO
M
Ret
urns
inte
rfac
e po
inte
r of
obj
ect t
o cl
ient
Mon
iker
7
Load
s its
sta
te fr
om fi
leO
bjec
t6
Inst
ruct
s ob
ject
to lo
ad p
revi
ousl
y st
ored
sta
teM
onik
er5
Cre
ates
obj
ect a
nd r
etur
ns in
terf
ace
poin
ter
to
mon
iker
Cla
ss o
bjec
t4
Load
s cl
ass
obje
ctS
CM
3
Look
s up
ass
ocia
ted
CLS
ID a
nd in
stru
cts
SC
M to
cr
eate
obj
ect
Mon
iker
2
Cal
ls B
indM
onik
erat
mon
iker
Clie
nt1
Des
crip
tio
nP
erfo
rmer
Ste
p
•O
nly
low
-leve
l nam
ing
•O
bjec
ts a
re o
nly
tran
sien
t. T
o ex
pand
an
obje
ct's
life
time,
add
ition
ally
a p
ersi
sten
t ob
ject
ref
eren
ce is
sto
red
to a
n ob
ject
. Thi
s re
fere
nce
is c
alle
d m
onik
er.
•M
onik
ers
have
all
info
rmat
ion
avai
labl
e to
rec
onst
ruct
an
obje
ctan
d re
load
its
stat
e
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
16
Ch
ap
ter
8:
Mid
dle
ware
Typ
es o
f M
on
iker
s Ref
eren
ce to
an
obje
ct in
a r
emot
e pr
oces
sP
oint
er m
onik
er
Ref
eren
ce to
a m
onik
er in
a c
ompo
sitio
nIte
m m
onik
er
Ref
eren
ce to
a c
ompo
sitio
n of
mon
iker
sC
ompo
site
mon
iker
Ref
eren
ce to
a c
lass
obj
ect
Cla
ss m
onik
er
Ref
eren
ce to
an
obje
ct c
onst
ruct
ed fr
om a
UR
LU
RL
mon
iker
Ref
eren
ce to
an
obje
ct c
onst
ruct
ed fr
om a
file
File
mon
iker
Des
crip
tio
nM
on
iker
typ
e
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
17
Ch
ap
ter
8:
Mid
dle
ware
Act
ive
Dir
ecto
ry•
Win
dow
s 20
00 c
onta
ins
a di
rect
ory
serv
ice
calle
d A
ctiv
e D
irect
ory
whi
ch c
an b
e us
ed b
y D
CO
M•
A d
istr
ibut
ed s
yste
m b
ased
on
Win
dow
s 20
00 is
par
titio
ned
into
dom
ains
con
sist
ing
of a
num
ber
of r
esou
rces
and
use
rs
•E
ach
dom
ain
has
a do
mai
n co
ntro
ller
whi
ch is
a lo
cal d
irect
ory
serv
er•
A d
omai
n co
ntro
ller
is im
plem
ente
d as
a L
DA
P d
irect
ory
serv
er
•LD
AP
ser
vers
are
reg
iste
red
in D
NS
•
Pro
blem
: a c
lient
has
to k
now
the
targ
et d
omai
n fo
r its
req
uest
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
18
Ch
ap
ter
8:
Mid
dle
ware
GL
OB
E
GL
obal
Obj
ect-
Bas
ed E
nviro
nmen
t
•E
xper
imen
tal d
istr
ibut
ed s
yste
m d
evel
oped
by
Vrij
eU
nive
rsite
itA
mst
erda
m
•D
esig
n go
al: s
uppo
rt h
uge
num
ber
of o
bjec
ts a
nd u
sers
spr
ead
acro
ss th
e In
tern
et,
scal
abili
ty is
cen
tral
rol
e
•F
unda
men
tal c
once
pt: h
ow a
re o
bjec
ts v
iew
ed?
�O
bjec
ts d
on't
only
enc
apsu
late
sta
te a
nd o
pera
tions
, but
add
ition
ally
they
en
caps
ulat
e th
e im
plem
enta
tion
of p
olic
ies
that
pre
scrib
e th
e di
strib
utio
n of
an
obje
ct's
sta
te a
cros
s m
ultip
le m
achi
nes
�E
ach
obje
ct d
eter
min
es h
ow it
s st
ate
is m
igra
ted,
rep
licat
ed o
r di
strib
uted
ove
r its
rep
licas
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
19
Ch
ap
ter
8:
Mid
dle
ware
Glo
be
Ob
ject
Mo
del
•N
ot u
ses
the
rem
ote
obje
ct m
odel
•O
bjec
ts, i
.e. t
heir
stat
es c
an b
e ph
ysic
ally
dis
trib
uted
(an
d re
plic
ated
). T
hey
are
calle
d di
strib
uted
sha
red
obje
cts
•E
ach
proc
ess
runn
ing
a 'p
art'
of a
n ob
ject
has
a lo
cal i
mpl
emen
tatio
n of
the
obje
ct's
inte
rfac
e im
plem
enta
tion
(loca
l rep
rese
ntat
ive,
loca
l obj
ect)
•E
ach
loca
l obj
ect o
ffers
an
inte
rfac
e SOInf
(sim
ilar
to IUnknown
in D
CO
M)
•Lo
cal o
bjec
ts im
plem
ent b
inar
y in
terf
aces
, int
erfa
ces
are
desc
ribed
usi
ng a
n ID
L
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
20
Ch
ap
ter
8:
Mid
dle
ware
Co
mp
ose
d O
bje
cts
Tw
o ki
nds
of lo
cal o
bjec
ts•
Prim
itive
loca
l obj
ect
•C
ompo
site
loca
l obj
ect:
com
pose
d of
sev
eral
prim
itive
or
com
pose
d lo
cal o
bjec
tsC
ompo
sitio
n is
use
d to
con
stru
ct a
usa
ble
loca
l obj
ect
•S
eman
tics
subo
bjec
tim
plem
ents
th
e fu
nctio
nalit
y
•C
omm
unic
atio
n su
bobj
ect
prov
ides
a s
tand
ard
inte
rfac
e to
th
e un
derly
ing
netw
ork;
it o
ffers
m
essa
ge-p
assi
ng p
rimiti
ves
for
com
mun
icat
ion
•R
eplic
atio
n su
bobj
ecti
mpl
emen
ts
the
obje
ct's
dis
trib
utio
n st
rate
gy
•C
ontr
ol s
ubob
ject
is in
term
edia
te
betw
een
user
inte
rfac
e an
d al
l ob
ject
func
tions
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
21
Ch
ap
ter
8:
Mid
dle
ware
Pro
cess
-to
-Ob
ject
Bin
din
g•
No
conc
epts
like
type
libr
ary
and
regi
stry
for
getti
ng in
terf
ace
desc
riptio
ns a
nd
activ
atin
g ob
ject
s.•
Use
d in
Glo
be:
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
22
Ch
ap
ter
8:
Mid
dle
ware
Co
mm
un
icat
ion
•O
nly
sync
hron
ous
com
mun
icat
ion
•S
ome
loca
l obj
ects
(he
re in
pro
cess
A)
can
be s
een
as p
roxi
es o
nly
forw
ardi
ng
requ
ests
•If
an o
bjec
t's s
tate
is r
eplic
ated
, the
rep
licat
ion
subo
bjec
tfor
war
ds th
e re
ques
t to
all
repl
icas
and
mer
ges
the
resu
lts
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
23
Ch
ap
ter
8:
Mid
dle
ware
Glo
be
Clie
nt
and
Ser
ver
Get
the
stat
us o
f a s
peci
fic lo
cal o
bjec
tS
tatL
R
Ret
urns
a li
st o
f all
loca
l obj
ects
for
a gi
ven
obje
cts
List
DS
O
Ret
urns
a li
st o
f all
loca
l obj
ects
List
All
Lets
the
serv
er r
emov
e al
l loc
al o
bjec
ts o
f a g
iven
obj
ect
Unb
indD
SO
Lets
the
serv
er r
emov
e a
loca
l obj
ect o
f a g
iven
obj
ect
Rem
oveL
R
Lets
the
serv
er c
reat
e a
loca
l obj
ect f
or a
new
dis
trib
uted
obj
ect
Cre
ateL
R
Lets
the
serv
er b
ind
to a
n ob
ject
, eve
n if
it is
alre
ady
boun
dA
ddB
indi
ng
Lets
the
serv
er b
ind
to a
giv
en o
bjec
t, un
less
it is
alre
ady
boun
dB
ind
Des
crip
tio
nM
eth
od
Clie
nt:
Pro
cess
bou
nd to
a d
istr
ibut
ed s
hare
d ob
ject
, inv
okin
g th
is o
bjec
t by
mak
ing
calls
at t
he c
ontr
ol s
ubob
ject
(pro
cess
A o
n th
e la
st s
lide)
Ser
ver
Pro
cess
that
can
han
dle
only
invo
catio
ns c
omin
g in
thro
ugh
the
netw
ork
(pro
cess
es B
and
C o
n th
e la
st s
lide)
Add
ition
ally
: ob
ject
ser
vers
for
supp
ortin
g di
strib
uted
sha
red
obje
cts/
host
ing
loca
l ob
ject
s. In
terf
ace
for
such
obj
ect s
erve
rs:
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
24
Ch
ap
ter
8:
Mid
dle
ware
Nam
ing
Ref
eren
ce to
a fi
le in
a c
lass
rep
osito
ry (
UR
L)Im
plem
enta
tion
hand
le
A p
roto
col-s
peci
fic a
ddre
ssP
roto
col a
ddre
ss
A c
onst
ant r
epre
sent
ing
a (k
now
n) p
roto
col
Pro
toco
l ide
ntifi
er
Des
crip
tio
nF
ield
•G
lobe
dis
tingu
ishe
s be
twee
n na
min
gan
d lo
catin
gob
ject
s•
Eac
h di
strib
uted
sha
red
obje
ct is
ass
igne
d a
glob
ally
uni
que
obje
ct id
entif
ier
(OID
)
•A
n ob
ject
han
dle
cont
ains
the
OID
•Lo
catio
n se
rvic
e is
org
anis
ed h
iera
rchi
cally
•T
he a
ddre
ss g
iven
bac
k by
the
loca
tion
serv
ice
can
be a
�S
tack
ed a
ddre
ss:
�In
stan
ce a
ddre
ss:
Str
ing
that
is u
sed
to in
itial
ize
an im
plem
enta
tion
Initi
aliz
atio
n st
ring
Ref
eren
ce to
a fi
le in
a c
lass
rep
osito
ryIm
plem
enta
tion
hand
le
Des
crip
tio
nF
ield
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
25
Ch
ap
ter
8:
Mid
dle
ware
Glo
be
Nam
ing
Ser
vice
Sim
ple
nam
ing
serv
ice
with
hum
an-f
riend
ly n
ames
:•
Bas
ed o
n D
NS
•N
ames
are
rep
rese
nted
by
a U
nifo
rm R
esou
rce
Iden
tifie
r (U
RI)
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