Methodologies for Design of Service-Based Systems - Intentional Perspectives on Information Systems Engineering - page 308

In such an approach the methodological approach to service design prevails, but
there is little focus on the potential offered by service-orientation is terms of adap-
tivity at run time. Some adaptivity is implied by using abstract service descriptions
and abstract processes with SLA annotations, however there is a need to better focus
on adaptation aspects.
As discussed in the previous section, adaptation can be considered both in the
design and in the run-time phases. In the design phase, there is a need to iden-
tify adaptive service behaviours and to specify the adaptation strategies that can be
applied at run time.
An initial attempt to go in the direction of the life cycle described in [ 3] , is pro-
posed in the PAWS (Processes with Adaptive Web Services) framework proposed in
[ 1] . In PAWS, processes are designed to be adaptive, where adaptation is prepared
at design time (Fig. 4) .
A process is designed as an abstract process, as proposed in previously illustrated
methods, but the choice of the suitable services to be invoked is performed at design
time. In fact, for each task a selection of potential services is provided at design
time, and interface adaptation and quality of service negotiation for the services

Process design

Service
registry

Advanced service
selection

Service preparation
(SLA negotiation, interface mediation)

Concrete
candidate
services

Flexible process

Local task
constraints

T1

Local task
constraints

T2 T3

T4

Global constraints

Process
execution

QoS optimization

context

Fig. 4 PAWS, processes with
adaptive web services [ 1]

Self-healing