Cloudware Technologies - Guide to Cloud Computing for Business and Technology Managers - page 322

and differentiating point between Web Services providers. This requires
not only focusing on the functional properties of services but also concen-
trating on describing the environment hosting the Web Service, that is,
describing the nonfunctional capabilities of services. Each service hosting
environment may offer various choices of QoS based on technical require-
ments regarding demands for around-the-clock levels of service availabil-
ity, performance and scalability, security and privacy policies, and so on, all
of which must be described.
In the Web Services' context, QoS can be viewed as providing assurance
on a set of quantitative characteristics. These can be defined on the basis
of important functional and nonfunctional service quality properties that
include implementation and deployment issues as well as other important
service characteristics such as service metering and cost, performance met-
rics (e.g., response time), security requirements, (transactional) integrity,
reliability, scalability, and availability. These characteristics are necessary
requirements to understand the overall behavior of a service so that other
applications and services can bind to it and execute it as part of a business
process.
Web Services QoS elements can be grouped under the following three
broad categories:
1. Performance and capacity : This category considers such issues as
transaction volumes, throughput rates, system sizing, utilization
levels, whether underlying systems have been designed and tested
to meet these peak load requirements, and, finally, how important
are request/response times.
2. Availability : This category considers such issues as mean time
between failure for all or parts of the system, disaster recovery
mechanisms, mean time to recovery, whether the business can toler-
ate Web Services downtime and how much, and whether there is
adequate redundancy built in so that services can be offered in the
event of a system or network failure.
3. Security/privacy : This category considers such issues as response to
systematic attempts to break into a system, privacy concerns, and
authentication/authorization mechanisms provided.
15.6 Summary
This chapter presented an overview of technologies on which cloud com-
puting depends: virtualization, service-oriented architectures (SOA), and
Web Services. Virtualization technology is one of the fundamental com-
ponents of cloud computing, Virtualization allows the creation of a secure,