Information Technology Reference
In-Depth Information
Requirement
I
O
Service process
N
i
o
Figure 3.3
Service composition: problem formulation.
as
I
and
O
, respectively. Thus, the requirement can be simply expressed as
I
o
,
that is, the operation consumes one instance of data type
i
and yields one
instance of data type
o
.
Our goal is to find a collection of operations in a large service
portfolio. These operations are connected to form a colored Petri net
N
.
As shown in Figure 3.3, the data type attached to one place is denoted as
an italic string.
We declare that
N
is a valid composition of the requirement
I
!
O
. Operations in a service portfolio can also be expressed as
i
!
!
O
if
1.
N
takes
i
as its only input and
o
as its only output;
2.
N
is data-coherent; and
3.
N
has some additional properties to be discussed later in
Section 3.3.2.
Before addressing the problem of service composition, we intro-
duce in the next section data-driven composition rules used to refine
processes in a business domain into processes in a service domain.
3.2 DATA-DRIVEN COMPOSITION RULES
The composition and transformation rules in this chapter are all
expressed with a graph transformation formalism. We believe that
this formalism is intuitive and thus easy to understand; more details
on graph transformation can be found in [88]. The sequential, parallel,
and choice composition rules correspond to the sequential, parallel, and
conditional routes given in a Workflow Net [81].