Information Technology Reference
In-Depth Information
2
G
is the Goal Tree of the organization, describing the dependencies
between different goals of the organization.
•
→
GT
:
G
2
R
relates a service with the set of roles that use it.
•
Client
:
S
→
2
R
relates a services with the set of roles that offer it.
•
Provider
:
S
→
2
G
describes the set of goals that can be achieved by a service,
thus defining the functionality of the system.
•
Obtains
:
S
→
2
G
•
Achieves
:
Ta
→
defines the set of goals that are reached when a task is
executed.
2
Ta
shows how services are split in different tasks.
•
Task
:
S
→
2
S
describes the dependencies between services, showing which
services need to be invoked by other services to complete their functionality,
thus allowing the composition of services.
•
Invoke
:
S
→
2
S
represents the sequence of services that must be followed in
order to achieve a goal.
•
Plan
:
G
→
Properties of the Relations.
The Goal Tree relation is irreflexive, asymmetrical and
transitive, since a goal cannot be related with itself, neither with its predecessor but it
can be related with the successors of its successors.
It must be assured that the provider of a service must be a role contained in the same
OU as the service. Formally:
∀
o
∈
OU
∧∀
s
∈
Services
(
o
)
→
Provider
(
s
)
⊆
Roles
(
o
)
(6)
This restriction assures that the services of an OU will be provided only inside it, but
they can be accessed by agents from other OUs (e.g. using the
Invoke
relation).
As pointed out in this section, the
Invoke
relation allows services to invoke other
services to reach their goals. In order to execute this operation, it must be assured that
the provider of the invoker service must be a client of the invoked service. Formally:
∀
s
1
,
s
2
∈
S
,
s
2
∈
Invokes
(
s
1
)
:
∀
r
1
∈
Provider
(
s
1
)
→∃
r
2
∈
Client
(
s
2
)
∧
r
1
=
r
2
(7)
A key issue for the system designer is to assure that the services located in an organiza-
tional unit must help to reach its goals. Formally, it is described as:
∀
o
∈
OU
,
∀
s
∈
Services
(
o
)
∧∀
g
1
∈
Pursues
(
s
)
:
∃
g
2
∈
Goals
(
o
)
→
g
2
∈
GT
(
g
1
)
(8)
It is is possible that a specific goal of a service could not be reached by any of the tasks
that compose it, so then this service must invoke another which should include at least
a task that achieves this desired goal. Formally, it is expressed as:
∀
g
∈
Obtains
(
s
1
)
→
(
∃
t
∈
Task
(
s
1
)
∧
g
∈
Achieves
(
t
))
∨
(
∃
s
2
∈
S
∧
g
∈
Obtains
(
s
2
)
∧
s
2
∈
Invokes
(
s
1
))
(9)
