Information Technology Reference
In-Depth Information
The following constraints make use of our rst-order extension of SLTL. This
extension was not part of the product delivered to SNI in 1995.
{
`
SIB',
making sure that counting is always properly initialized. The parameter is
only used to identify dierent counters within the same service.
counter
SIBs are only allowed to appear after a corresponding
init
8n:
counter
n
)
init
n
(
)
BF
(
(
))
{
More complicated is the following constraint guaranteeing pathwise version
compatibility: `on every path, where
SIB1
occurs in version
n
, each subse-
quent occurrence of
SIB2
is at least of version
n
+2'.
8n:
Version(SIB1
)=
n )
G
(
Version(SIB2
)
n
+2)
{
Finally, it is also possible to express global version consistency properties,
like: `whenever a SIB occurs in version
n
within a service, then all its occur-
rences are of version
n
'.
8n: :
G
(
:
Version(SIB
)=
n
)
)
G
(
Version(SIB
)=
n
)
In fact, in discussions with application experts it turned out that only very
few simple patterns of constraints are required in order to express most of the
desired properties. Thus application experts should be able to input their own
constraints on the basis of very few corresponding templates.
3.6
Safe Service Customization
The incremental formalization approach, where (global) constraints are added
online, aims at establishing a (loose) correctness lter but is far from guaran-
teeing correctness. Thus that responsibility remains with the programming or
application expert. This approach is not applicable for customizers, subscribers
or end users: they require a dual assistance, which constrains their freedom of
design in order to guarantee consistency and executability.
Safe Service Cus-
tomization
[6] is such a technique. It flexibly supports subscribers in their desire
of modifying the
service logic
in a controlled fashion, while guaranteeing that the
modied services can immediately be activated, without previous intervention
of specialists like service designers or testers. Thus it goes far beyond the usual
service adaptation capabilities, which either
{
concern user-specic data only, like changing the PIN or modifying the time
windows or the destination numbers for some routings, or
{
are restricted to the combination of a small selection of Features or Service
Independent Building Blocks, like e.g. those for call center functionality.
Together with its call flow-oriented user interface, our technique satises the
following two requirements, essential for success in a competitive market:
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