An Ini ial App oach o Explaining SLA
Inconsis encies?
Ca los Mülle , An onio Ruiz-Co és, Manuel Resinas
Dp o. Lenguajes y Sis emas In o má icos
ETS. Ingenie ía In o má ica - Uni e sidad de Se illa (Spain - España)
41012 Se illa (Spain - España)
{cmulle , a uiz, esinas}@us.es
Abs ac An SLA signed by all in e es ed pa ies mus be c ea ed ca e-
ully, a oiding con adic ions be ween e ms, because hei e ms could
ca y penal ies in case o ailu e. Howe e , his consis ency checking may
become a challenging ask depending on he complexi y o he ag ee-
men . As a consequence, an au oma ed way o checking he consis ency
o an SLA documen and e u ning he se o inconsis en e ms o he
ag eemen would be e y appealing om a p ac ical poin o iew. Fo
ins ance, i enables he de elopmen o so wa e ools ha make he c e-
a ion o co ec SLAs and he consis ency checking o impo ed SLAs
easie o use s. In his pape , we p esen he p oblem o explaining WS-
Ag eemen inconsis encies as a cons ain sa is ac ion p oblem (CSP),
and hen we use a CSP sol e oge he wi h an explana ion engine o
check he consis ency and e u n he inconsis en e ms. Fu he mo e, a
p oo -o -concep using Choco sol e in conjunc ion wi h he Palm expla-
na ion engine has been de eloped.
Keywo ds: Se ice Le el Ag eemen , WS-Ag eemen , Consis ency Check-
ing, Debugging, Quali y o Se ice.
1 In oduc ion
SLAs consis o a se o e ms ha include in o ma ion abou unc ional ea u es,
non- unc ional gua an ees, compensa ion, e mina ion e ms and any o he e ms
wi h ele an in o ma ion o he ag eemen . An ag eemen signed by all in e -
es ed pa ies should be edac ed ca e ully because a ailu e o speci y hei e ms
could ca y penal ies o he ini ia ing o esponding pa y. The e o e, ag eemen
e ms should be speci ied in a consis en way, a oiding con adic ions be ween
hem. Howe e , depending on he complexi y o he ag eemen , his may be-
come a challenging ask. Fo ins ance, in a scena io in which a p o ide o e s
compu ing se ices o o he o ganiza ions, an SLA could be ag eed ha includes
non- unc ional a ibu es such as: he a ailabili y -in pe cen age-, he mean ime
be ween wo consecu i e eques s o he se ice (MTBR) -in seconds-, and he
?This wo k has been pa ially suppo ed by he Eu opean Commission (FEDER),
Spanish Go e nmen unde CICYT p ojec Web-Fac o ies (TIN2006-00472), and
p ojec P07-TIC-2533 unded by he Andalusian local Go e nmen .
e iciency. Assuming ha : A ailabili y anges be ween [90..100] , MTBR anges
be ween ∈[5..60] and E iciency =A ailabili y/MTBR. I he SLA includes a
e m obliga ing o gua an ee E iciency >20, a i s sigh he SLA is consis en .
Howe e he highes alid alue o e iciency is 100/5=20, so his e m canno
be sa is ied. The e o e, a consis ency checke ha au oma ically checks he SLA
o inconsis encies be ween i s e ms would be e y appealing om a p ac ical
poin o iew.
Fu he mo e, i is o in e es no only o ob ain an au oma ed way o check-
ing he consis ency o an SLA documen , bu also o e u n an explana ion i he
documen is inconsis en . This explana ion is he se o inconsis en e ms o he
ag eemen . So, in he p e ious scena io we would ob ain as debugging in o ma-
ion ha he inconsis en e ms a e: [(E iciency >20),(A ailabili y ∈[90..100]),
(MTBR ∈[5..60]),(E iciency =A ailabili y/MTBR)], because hey a e incon-
sis en e ms. This au oma ed consis ency checking enables he implemen a ion
o a so wa e ool which makes he c ea ion o co ec SLAs and he consis ency
checking o impo ed SLAs easie o use s.
Ne e heless, as a as we know, he consis ency o SLAs has been aken o
g an ed by mos au ho s. In his pape , we desc ibe a mechanism o check and
explain SLAs speci ied wi h WS-Ag eemen [2], which is a p oposed ecommen-
da ion o he Open G id Fo um (OGF) which p o ides a schema o de ining
SLAs and a p o ocol o c ea ing hem. To his end, we map he e ms o a
subse o he WS-Ag eemen documen in o a cons ain sa is ac ion p oblem
(CSP). Then we use he CSP as an inpu o a CSP sol e wi h an explana ion
engine, which will e u n he se o inconsis en cons ain s. Finally, we ace
back he cons ain s o he o iginal SLA e ms in o de o gi e use ul debugging
in o ma ion o use s.
As a p oo -o -concep , we ha e de eloped a p o o ype o ou consis ency
analyse using Choco sol e [1] in conjunc ion wi h he Palm explana ion engine
[3]. This p o o ype is a ailable o es ing a h p://www.isa.us.es in he ools
sec ion.
This pape is s uc u ed as ollows. Sec ion 2 p esen s some backg ound on
cons ain sa is ac ion p oblems and WS-Ag eemen . Sec ion 3 de ails he sub-
se o WS-Ag eemen which is used o explain he SLA inconsis encies in 3.1
and i s mapping o CSP in 3.2. Sec ion 4 desc ibes ou p ocess o explain he
WS-Ag eemen * iconsis encies. Sec ion 5 shows ou p oo -o -concep . Sec ion 6
epo s on he ela ed p oposals. Finally, Sec ion 7 de ails ou conclusions and
u u e wo k.
2 P elimina ies
2.1 Cons ain Sa is ac ion P oblems
Cons ain Sa is ac ion P oblems [8] ha e been he objec o esea ch in A i icial
In elligence o e he las ew decades. A Cons ain Sa is ac ion P oblem (CSP)
is de ined as a se o a iables, each anging on a ini e domain, and a se o
cons ain s es ic ing all he alues ha hese a iables can ake simul aneously.
A solu ion o a CSP is an assignmen o a alue om i s domain o e e y a iable,
in such a way ha all cons ain s a e sa is ied simul aneously. These a e some
basic de ini ions o wha a CSP is.
De ini ion 1 (CSP). A CSP is a h ee– uple o he o m (V, D, C)whe e V6=∅
is a ini e se o a iables, D6=∅is a ini e se o domains (one o each a iable)
and Cis a cons ain de ined on V.
Conside , o ins ance, he CSP: ({a, b},{[0..2],[0..2]},{a+b < 4})
De ini ion 2 (Solu ion). Le ψbe a CSP, a solu ion o ψis wha e e alid
assignmen o all elemen s in V ha sa is ies C.
In he p e ious example, a possible solu ion is (2,0) since i e i ies ha
2+0<4.
De ini ion 3 (Solu ion space). Le ψbe a CSP o he o m (V, D, C), i s
solu ion space deno ed as sol(ψ)is made up o all i s possible solu ions. A CSP
is sa is iable i i s solu ion space is no emp y.
sol(ψ) = {S| ∀si·si∈S⇒C(si) = ue}
In he p e ious example he e a e eigh solu ions. The only assignmen ha
does no sa is y a+b < 4is (2,2). Ne e heless, i we eplace he cons ain wi h
a+b < −1, hen he CSP is no sa is iable.
In many eal-li e applica ions, i a CSP has no solu ion, we would like o know
which se o cons ain s a e esponsible o his si ua ion. This can be done by
in e p e ing he CSP as an explana ion p oblem.
De ini ion 4 (Explana ion p oblem). Le be a CSP o he o m (V, D, C)
wi h an emp y solu ion space: sol() = ∅. I is conside ed o be an explana ion
p oblem i i s objec i e is o ind a se o cons ain s C0⊂C ha canno be
sa is ied.
De ini ion 5 (Explana ions). Le be an explana ion p oblem, he esul ing
se o inconsis en cons ain s C0a e known as he explana ions o he p oblem.
They a e di ided in o wo pa s: a subse o he o iginal se o cons ain s C0⊂C
and a subse o decision cons ain s in oduced so a in he sea ch o solu ions
(dc1, ..., dck).
As de ined in [3], a con adic ion explana ion, also known as “nogood” [7], is a
subse o he cons ain s o he p oblem ha , le alone, leads o a con adic ion
(no easible solu ion con ains a nogood).
The p e ious CSP example, wi h he cons ain eplaced wi h a+b < −1, is
no sa is iable, and by in e p e ing i as an explana ion p oblem he explana ion
engine should ob ain as he se o inconsis en cons ain s: [(a+b < −1),(a >=
0),(b >= 0)]
2.2 WS-Ag eemen in a Nu shell
WS-Ag eemen speci ies an XML-based language and a p o ocol o ad e ising
he capabili ies and p e e ences o se ice p o ide s, and c ea ing ag eemen s
based on ag eemen o e s. The s uc u e o an ag eemen in WS-Ag eemen
comp ises:
– Name: i iden i ies he ag eemen and can be used o e e ence.
– Con ex : i includes in o ma ion such as he name o he pa ies and hei
oles as ini ia o o esponde in he ag eemen . Addi ionally, i can include
o he impo an in o ma ion o he ag eemen .
– Te ms: hey a e g ouped by he ollowing e m composi o s: Exac lyOne,
OneO Mo e, o All. The wo main ypes o e ms a e:
•Se ice e ms: hey p o ide se ice in o ma ion by means o :
∗Se ice desc ip ion e ms and se ice e e ences, which includes in o -
ma ion o ins an ia e o iden i y he se ices and ope a ions in ol ed
in he ag eemen .
∗Se ice p ope ies, which includes he measu able p ope ies ha
a e used in exp essing gua an ee e ms. They consis o a se o a i-
ables whose alues can be es ablished inside he se ice desc ip ion
e m, and whose domain can be es ablished by he me ic a ibu e
poin ing o an ex e nal XML documen .
•Gua an ee e ms: hey desc ibe he se ice le el objec i es (SLO) ag eed
by a speci ic obliga ed pa y, ei he using a ee- o m elemen o using a
key pe o mance indica o . I also includes he scope o he e m (e.g. i i
applies o a ce ain ope a ion o a se ice o he whole se ice i sel ), and
a quali ying condi ion ha speci ies he alidi y condi ion unde which
he e m is applied.
Figu e 1 depic s an example o a WS-Ag eemen be ween a compu ing se -
ices p o ide and a consume . I de ines se e al se ice p ope ies whose domain
is speci ied in an ex e nal XML documen (depic ed in Figu e 2). No e ha o he
XML documen s, such as an XML Schema de ini ion, could ha e been used in-
s ead. The se ice p ope ies de ined in he WS-Ag eemen documen o Figu e
1 a e he ollowing ones:
– he a ailabili y -in ege o m 1 o 100-
– he mean ime be ween wo consecu i e eques s o he se ice (MTBR) -
in ege g ea e han 1-
– he mean ime o esponse (MTTR) -in ege g ea e han 1-
– he ini ial cos o he se ice (Ini Cos ) -in ege g ea e han 1-
– he inal cos o he se ice (Cos ) -in ege g ea e han 1-
– he inc ease o he cos i he MTBR < 10 (Ex aMTBRCos ) -in ege
g ea e han 1-
– he inc ease o he cos i he MTTR < 05 (Ex aMTTRCos ) -in ege
g ea e han 1-
We ha e ex ac ed he ollowing in o ma ion om he SLA:
–MTBR ∈[5..60].
–MTTR ∈[1..10].
–I MTBR >= 10 Then A ailabili y ∈[90..100].
–I MTBR < 10 Then A ailabili y ∈[95..100].
–Cos = Ini Cos + Ex aMTBRCos + Ex aMTTRCos .
–I MTBR < 10 Then Ex aMTBRCos = 15.
–I MTTR < 05 Then Ex aMTTRCos = 15.
–I MTBR >= 10 and MTTR >= 05 Then Ex aMTBRCos = 0 and Ex-
aMTTRCos = 0.
3 Mapping WS-Ag eemen on o CSP
3.1 WS-Ag eemen * as a subse o WS-Ag eemen
Due o he lexibili y and ex ensibili y o WS-Ag eemen , we ocus in his pape
on a subse o WS-Ag eemen ha is a bi less exp essi e han WS-Ag eemen ,
bu s ill use ul o ou pu pose. The subse o WS-Ag eemen is called WS-
Ag eemen *. A WS-Ag eemen * documen (α) is composed o he ollowing el-
emen s:
–Se ice p ope ies mus de ine all a iables ha a e used in he gua an ee
e ms. In addi ion, a ibu e me ic o he a iables is manda o y. This
a ibu e mus poin o ano he XML documen o schema ha p o ides
he da a ype and a gene al ange o alues (δ) o each se ice p ope y.
Figu e 2 shows an example o an ad-hoc XML documen ha includes he
men ioned in o ma ion o se ice p ope ies o he example o Figu e 1,
al hough o he XML documen s could be used. XML node Loca ion (λυ) o
each a iable es ablishes he speci ic XML node inside he se ice desc ip ion
e m whe e i is de ined he alue o such a iable ( alue(λυ)).
–Te ms (T) can be composed using he h ee e m composi o s de ined in
WS-Ag eemen : All (), Exac lyOne (⊗), and OneO Mo e (⊕).
–Se ice desc ip ion e ms can be included bu only o impose speci ic alue
de ini ions o each a iable (υ) o se ice p ope ies. O he se ice desc ip-
ion e ms could be added bu hey a e igno ed when checking he SLA
consis ency.
–Gua an ee e ms (γ) can be included. Bo h quali ying condi ion (κ) and
he SLOs (σ) mus be de ined as cons ain s on he a iables de ined in he
se ice p ope ies, and only o hose a iables (i.e. κ∈Cand σ∈C). The
scope o a gua an ee e m canno be es ablished, bu all gua an ee e ms
apply o he whole se ice.
No e ha , al hough WS-Ag eemen * is no as exp essi e as WS-Ag eemen ,
i does allow o he exp ession o complex ag eemen s. Fo ins ance, he ag ee-
men depic ed in Figu e 1 is compa ible wi h WS-Ag eemen *.
Thus, we can o mally de ine an ag eemen speci ied wi h WS-Ag eemen *
as ollows:

<Ag eemen ’’id=exampleScena io’’>
<Con ex > ... </...>
<All>
<Se iceDesc ip ionTe m Name=’’Compu ingSe ice’’>
<...>
... </...>
<Ini Cos > 20 </...>
... </...>
</...>
</Se iceDesc ip ionTe m>
<Se iceP ope ies>
...<Va iable name=’’A ailabili y’’ me ic=’’me icXML:A ailabili y’’>
<Loca ion> A ailabili y </Loca ion>
</Va iable>
<Va iable name=’’MTBR’’ me ic=’’me icXML:MTBR’’>
<Loca ion> MTBR </Loca ion>
</Va iable>
<Va iable name=’’MTTR’’ me ic=’’me icXML:MTTR’’>
<Loca ion> MTTR </Loca ion>
</Va iable>
<Va iable name=’’Ini Cos ’’ me ic=’’me icXML:Ini Cos ’’>
<Loca ion> Ini Cos </Loca ion>
</Va iable>
<Va iable name=’’Cos ’’ me ic=’’me icXML:Cos ’’>
<Loca ion> Cos </Loca ion>
</Va iable>
<Va iable name=’’Ex aMTBRCos ’’ me ic=’’me icXML:Ex aMTBRCos ’’>
<Loca ion> Ex aMTBRCos </Loca ion>
</Va iable>
<Va iable name=’’Ex aMTTRCos ’’ me ic=’’me icXML:Ex aMTTRCos ’’>
<Loca ion> Ex aMTTRCos </Loca ion>
</Va iable>...
</Se iceP ope ies>
<Gua an eeTe m Name=’’MTBRDomain’’>
<SLO> MTBR >= 5 and MTBR <= 60 </...>
</Gua an eeTe m>
<Gua an eeTe m Name=’’MTTRDomain’’>
<SLO> MTTR >= 1 and MTTR <= 10 </...>
</Gua an eeTe m>
<Gua an eeTe m Name=’’Cos De ini ion’’>
<SLO> Cos = Ini Cos + Ex aMTBRCos + Ex aMTTRCos </...>
</Gua an eeTe m>
<Exac lyOne>
<Gua an eeTe m Name=’’Lowe A ailabili yDomain’’>
<Quali yingCondi ion> MTBR >= 10 </...>
<SLO> A ailabili y >= 90 and A ailabili y <= 100 </...>
</Gua an eeTe m>
<Gua an eeTe m Name=’’Highe A ailabili yDomain’’>
<Quali yingCondi ion> MTBR < 10 </...>
<SLO> A ailabili y >= 95 and A ailabili y <= 100 </...>
</Gua an eeTe m>
</Exac lyOne>
<OneO Mo e>
<Gua an eeTe m Name=’’MTBRInc emen ’’>
<Quali yingCondi ion> MTBR < 10 </...>
<SLO> Ex aMTBRCos = 15 </...>
</Gua an eeTe m>
<Gua an eeTe m Name=’’MTTRInc emen ’’>
<Quali yingCondi ion> MTTR < 05 </...>
<SLO> Ex aMTTRCos = 15 </...>
</Gua an eeTe m>
<Gua an eeTe m Name=’’Cheape Cos ’’>
<Quali yingCondi ion> MTBR >= 10 and MTTR >= 05 </...>
<SLO> Ex aMTBRCos = 0 and Ex aMTTRCos = 0 </...>
</Gua an eeTe m>
</OneO Mo e>
</All>
</Ag eemen >
Figu e 1. Example o a WS-Ag eemen documen wi h all kinds o composi o s.
<me icXML>
<A ailabili y ype=’’in ege ’’ min=’’1’’ max=’’100’’/>
<MTBR ype=’’in ege ’’ min=’’1’’ max=’’unbounded’’/>
<MTTR ype=’’in ege ’’ min=’’1’’ max=’’unbounded’’/>
<Ini Cos ype=’’in ege ’’ min=’’1’’ max=’’unbounded’’/>
<Cos ype=’’in ege ’’ min=’’1’’ max=’’unbounded’’/>
<Ex aMTBRCos ype=’’in ege ’’ min=’’1’’ max=’’unbounded’’/>
<Ex aMTTRCos ype=’’in ege ’’ min=’’1’ max=’’unbounded’’/>
</me icXML>
Figu e 2. Ad-hoc XML documen o he a iable domains o Figu e 1.
De ini ion 6 (A WS-Ag eemen * documen ). A WS-Ag eemen * docu-
men αis a se o a iables υi, a iable domains δi, and a se o e ms T,
including se ice desc ip ion e ms, gua an ee e ms and e ms composi o s as
ollows:
α= (υi, . . . , υn, δi, . . . , δn, T1, . . . , Tm),whe e Ti=











λυ
γ
Ti1. . . Tik
Ti1⊗. . . ⊗Tik
Ti1⊕. . . ⊕Tik











3.2 Mapping WS-Ag eemen * on o CSP
Figu e 3 depic s he mapping (µ) o a WS-Ag eemen * documen (α) on o an
equi alen CSP, (ψα). The a iables (υ) de ined inside he se ice p ope ies a e
he CSP a iables; he a iable domains (δ) included in he documen speci ied
by he me ic a ibu e a e he CSP a iable domains; and he cons ain s om
he se ice desc ip ion e ms (λυ), gua an ee e ms (γ) and e m composi o s
(as a logic “AND”, ⊗as logic “XOR”, and ⊕as logic “OR”) a e he CSP
cons ain s.
Thus, in gene al, ou WS-Ag eemen * o CSP mapping can be de ined as
ollows:
De ini ion 7 (Mapping an WS-Ag eemen * o CSP). The mapping (µ:
α→ψ) o a WS-Ag eemen * documen (α) o a CSP (ψ) can be de ined as
ollows:
µ(α) = µ(υ1, . . . , υn, δ1, . . . , δn, T1, . . . , Tm) =
= ({υ1, . . . , υn},{δ1, . . . , δn},{µT(T1, . . . , Tm)}) = ψα
whe e µT:T→Cis a mapping unc ion o e ms in o cons ain s de ined as
ollows:
µT(T)≡











υ=λυi Tis a se ice desc ip ion e m (λυ)
σi Tis a gua an ee e m wi hou quali ying condi ion (γσ)
κ⇒σi Tis a gua an ee e m wi h a quali ying condi ion (γσ,κ)
Vk
i=1 µT(Ti)i Tis a composi e e m (T1. . . Tk)
Vk
i=1 µT(Ti)⇔(Vk
j=1 j6=i¬µT(Tj)) i Tis a composi e e m (T1⊗. . . ⊗Tk)
Wk
i=1 µT(Ti)i Tis a composi e e m (T1⊕. . . ⊕Tk)











<Ag eemen >
<o o >
<Se iceP ope ies>
…< a iable name=‘’ 1’’ me ic=‘‘me icXML:δ1’’>
<loca ion> 1 </…>
</ a iable> …
…< a iable name=‘‘ n’’ me ic=‘‘me icXML:δn’’>
<loca ion> n </…>
</ a iable> …
</Se iceP ope ies>
<Se iceDesc ip ionTe m ( 1)>
…< 1> alue( 1)</ 1> …
<n> alue( n)</ n> …
</Se iceDesc ip ionTe m>
<Gua an eeTe m name=‘‘ 1’’ ( 2)>
<SLO> </SLO>
</Gua an eeTe m>
<Gua an eeTe m name=‘‘ m’’ ( k)>
<Quali yingCondi ion> </Quali yingCondi ion>
<SLO> </SLO>
</Gua an eeTe m>
</o o >
</Ag eemen >
<<WS-Ag eemen *>>
<me icXML>
<δ1 ype=‘‘…’’ min=‘‘…’’ max=‘‘…’’> …
<δn ype=‘‘…’’ min=‘‘…’’ max=‘‘…’’>
</me icXML>
<<me icXML>>
CSP
a iables
={
(Equi alen CSP)
CSP
a iable
domains
CSP
cons ain s
1,
…,
n,
δ1,
…,
δn,
1,
…,
m
(i)≡ i = alue( i)
(1)≡
i≡ i
(m)≡
(o o )
δi≡ δi
{
{
{
{
{
(
(
Figu e 3. Summa y o WS-Ag eemen * o CSP mapping.
Using his mapping, he ψα o he example o Figu e 1 is mapped as ollows:
ψα= ( { A ailabili y, MTBR, MTTR, Ini Cos , Cos , Ex aMTBRCos , Ex aMTTRCos },
{[1. . . 100 ], [ 1 . . . ∞), [ 1 . . . ∞), [ 1 . . . ∞), [ 1 . . . ∞), [ 1 . . . ∞), [ 1 . . . ∞), },
{ Ini Cos = 20,
MTBR ≥5 and MTBR ≤60,
MTTR ≥1 and MTBR ≤10,
Cos = Ini Cos + Ex aMTBRCos + Ex aMTTRCos ,
((MTBR ≥10) ⇒(A ailabili y ≥90 and A ailabili y ≤100)) ⇔
⇔ ¬ ((MTBR < 10) ⇒(A ailabili y ≥95 and A ailabili y ≤100)),
(MTBR < 10 ⇒Ex aMTBRCos = 15) ∨
∨(MTTR < 5 ⇒Ex aMTTRCos = 15) ∨
∨((MTBR ≥10 and MTTR ≥5) ⇒Ex aMTBRCos = 0 and Ex aMTTRCos = 0) }
)
The ollowing able deno es cons ain s mapped om he example o Figu e
1.
Example e m (Ti) name Equi alen mapped (µT(Ti))
Ini Cos Ini Cos = 20
MTBRDomain MTBR >= 5 and MTBR <= 60
MTTRDomain MTTR >= 1 and MTTR <= 10
Cos De ini ion Cos = Ini Cos + Ex aMTBRCos + Ex aMTTRCos
Lowe A ailabili yDomain (MTBR ≥10) ⇒(A ailabili y ≥90 and
A ailabili y ≤100)
Highe A ailabili yDomain (MTBR < 10) ⇒(A ailabili y ≥95 and
A ailabili y ≤100)
MTBRInc emen (MTBR < 10) ⇒(Ex aMTBRCos = 15)
MTTRInc emen (MTTR < 5) ⇒(Ex aMTTRCos = 15)
Cheape Cos (MTBR ≥10 and MTTR ≥5) ⇒
(Ex aMTBRCos = Ex aMTTRCos = 0)
Exac lyOne (Lowe A ailabili yDomain ⇔ ¬ Highe A ailabili yDomain) ∧
(Highe A ailabili yDomain ⇔ ¬ Lowe A ailabili yDomain)
OneO Mo e MTBRInc emen ∨MTTRInc emen ∨Cheape Cos
All Ini Cos ∧MTBRDomain ∧MTTRDomain ∧
∧Cos De ini ion ∧Exac lyOne ∧OneO Mo e
Table 1. Mapping example e ms o CSP cons ain s
4 Checking and Explaining WS-Ag eemen *
Inconsis encies
Checking he consis ency o WS-Ag eemen documen s in ol es bo h syn ac ic
and seman ic checking. The o me in ol es checking he documen agains he
WS-Ag eemen XML Schema. The la e , howe e , is ha de o check on and is
hus he ocus o his pape .
Figu e 4 depic s ou consis ency checking p ocess. In his scena io, i is im-
posed by a human e o , an MTBR alue de ini ion inside he se ice desc ip ion
e m wi h a alue o 61. Thus, he ψαwould no be sa is iable by he MTBR
domain de ini ion. As depic ed in Figu e 4, we p opose o use he ag eemen
speci ied wi h WS-Ag eemen * in conjunc ion wi h he XML documen which
de ines he a iables me ics as he wo inpu s o a mapping componen which
implemen s he mapping de ined in sec ion 3.2. Once he ag eemen is mapped
o a CSP, he explana ion engine o he CSP explaine componen will ob ain
whe he he SLA documen is consis en o no . In he la e case, he componen
sends o a acing componen he explana ions o he p oblem. In his case, he
explana ions o he p oblem a e MT BR: [MTBR = 61; MTBR ≥5 and MTBR
≤60]. The acing componen con e s he explana ions in o he equi alen in-
consis en o iginal e ms in o de o gi e use ul in o ma ion o use s. This is
done by naming cons ain s mapped om an SLO as he name o he gua an ee
e m which includes i ; and i he cons ain was mapped om a alue de ini ion
inside a se ice desc ip ion e m, we name i “SDT”, conca ena e wi h he name
o he a iable. Then, he p e ious explana ion o MTBR would be aced by us
o he inconsis en e m “SDTMTBR” cons ain , showing ha i is he MTBR