QoS-Oriented Service Computing - Advanced Design Approaches to Emerging Software Systems - page 285

Invoice Manager into low-level infrastructural parameters

(such as CPU, bandwidth, memory usage)
that can be quantitatively measured (usual-
ly supported by OS probes). This mapping
happens on the basis of (i) SLA template
instance, (ii) domain-specific schemas, or
(iii) domain-specific ontology.

The Invoice Manager works out the bill which
includes usage charging, penalty charging, etc.
The calculation will reference to SLA instance or
domain-specific ontology.

Policy Store • Violation Evaluator: (i) Analyze the gath-

ered data and send notification message
to the Enforcement Engine when threat
thresholds are reached. The Enforcement
Engine will then take some recovery ac-
tions so that values can return to normal
execution level (ii) Although the alert
thresholds are defined in SLA, an interface
allowing on-the-fly modification of the
alarm thresholds should be supported, and
(iii) should allow graphical visualization of
the metrics.

Stores the domain polices which will be used to
decide the recovery actions or rescheduling. It
usually works with the Rule Engine .

SLA Template

The SLA template describes the bi-partite con-
tract between service provider and customer. The
contract content should be provided by service
provider and typically should have: (i) Contract Id:
Uniquely identify a contract. (ii) Context: Various
metadata about the context, e.g. contact duration,
consumer name, service provider name, etc. (iii)
Service Description Terms (SDT): Define the
functionality this contact promises to deliver. It is
domain specific. (iv) Service Properties: Define
measurable and exposed properties related to a
service. The properties are used to describe the
service level objectives. (v) Guarantee Terms: Pro-
vide assurance on the service quality or resource
availability offered by a service provider, and
(vi) Business Terms: Usage charging or penalty.
The survey has shown that WS-Agreement is an
appropriate standard for the representation of the
SLA template.

• Report generator: Generate usage report

periodically.

Enforcement Engine

The Enforcement Engine component module
aims to ensure that terms defined in SLA can be
guaranteed. It contains the following sub-modules:

• Notifier: Will send notification message to

service provider or customer when viola-
tion event happens.

• Rule Engine: Based on the feature of the

event, the Rule Engine will (i) retrieve
relevant policy from the Policy Store , (ii)
get parameters from SLA instance, or (iii)
domain knowledge from the ontology, to-
gether to decide the recovery actions or
rescheduling.

SLA Instance

Once terms and agreement of SLA have been
agreed by both service provider and service
consumer after negotiation, the SLA becomes
an SLA instance. It serves as a signed contract
between both parties.

• Trigger: Responsible for taking recovery

actions or rescheduling instructed by the
Rule Engine . For example, to get a new
service deployed, or get a new session
created.