MetaFrame in Practice: Design of Intelligent Network Services - Correct System Design: Recent Insights and Advances - page 381

Strengthening of the Environment. Application development is superposed by
an orthogonal process of incremental strengthening of the application-specic
environment: this happens by successively adding further BBs and consistency
constraints. Both strengthenings proceed naturally, on demand: new BBs may
turn out to become necessary when the range of the environment or the applica-
tion are enlarged, or when it becomes obvious that certain code fragments have
a high potential for reuse. The latter situation is supported by 's

macro facility [23], which essentially allows one to encapsulate (fragments of)
application programs as BBs. In the further development process, these blocks
can be used just as `ordinary' BBs.
New constraints naturally arise when an erroneous BB combination pattern
is detected in the test lab, or when new versions of BBs impose or induce com-
patibility constraints.

M eta Frame

M eta Frame explicitly separates BB implementations from their descriptions: for

each application domain we have a distinct Meta-Data repository containing an
abstract description of the BBs. The BBs themselves and their documentation
are available in a dierent repository. As prototyping can start already as soon
as the abstract description level of a domain is available, application experts can
experiment with the combination of new BBs independently of their direct phys-
ical availability. This experimentation phase may in fact influence the choice and
design of new BBs. In fact,

explicitly encourages feedback flowing
from the application experts to the programming experts by allowing abstract
descriptions of BBs to be associated with simulation code, in order to prototyp-
ically use new BBs before they are actually implemented.

M eta Frame

Rather than providing a technical description of all these features and their
impact, we will illustrate them along an industrial application: the design of
intelligent network (IN) services. We gained experience in the area during an
intense industrial cooperation in 1995/96, which led to a product that has been
adopted, bought, and marketed by Siemens Nixdorf Informationssysteme AG
(SNI) [20, 22, 23, 5, 21].

1.2 Intelligent Network Services.

Intelligent Networks have changed the world of telecommunication in the last
decade: by integrating telecommunication and computer technology, the Intel-
ligent Network concept (see [9] for an overview) helps (network) providers to
make new and flexible telecommunication services available to their customers.
Concretely, complex programs steer the call handling of special telephone ser-
vices, ranging from simple Free Phone services, where the called party pays the
bill, to ambitious Virtual Private Network services establishing a distributed,
private telephone network for a group of users within the public network.
In fact, practically everybody has already made use of IN services. Partic-
ularly widespread examples are Televoting, Personal Mobility services, or Pre-
mium Rate Services, which enable the service subscriber to supply certain in-