Cloud Computing Support for Construction Collaboration - Mobile and Pervasive Computing in Construction - page 240

The National Institute of Standards and Technology (NIST) in the United States
defined cloud computing as “a model for enabling ubiquitous, convenient, on-
demand network access to a shared pool of configurable computing resources (e.g.
networks, servers, storage, applications, and services) that can be rapidly provisioned
and released with minimal management effort or service provider interaction. This
cloud model promotes availability and is composed of five essential characteristics -
(1) on-demand self-service, (2) broad network access, (3) resource pooling, (4) rapid
elasticity, and (5) measured service” (Mell and Grance, 2011).
Vaquero et al. (2009) have studied more than 20 definitions and proposed the
following definitions for cloud computing:“Clouds are a large pool of easily usable
and accessible virtualized resources (such as hardware, development platforms and/or
services). These resources can be dynamically re-configured to adjust to a variable
load (scale), allowing also for an optimum resource utilization. This pool of resources
is typically exploited by a pay-per-use model in which guarantees are offered
by the Infrastructure Provider by means of customized Service-Level Agreements
(SLAs)”.
Some people question the innovation of cloud computing. According to Youseff
et al. (2008), cloud computing is a new computing model that consists of new
concepts/technologies and existing concepts/technologies, or their enhancement:
“Cloud computing is a collection of many old and few new concepts in several research
fields like Service-Oriented Architectures (SOA), distributed and grid computing as
well as Virtualization. Cloud computing can be considered a new computing paradigm
that allows users to temporary utilize computing infrastructure over the network,
supplied as a service by the cloud-provider at possibly one or more levels of abstraction”.
12.2.1 Service delivery models - SaaS, PaaS, and IaaS
The essence of cloud computing is the delivery of IT resources in the form of service
units. Cloud computing services are widely classified into three types - Software as a
Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS).
Rhoton (2010) divides a cloud computing environment into five tiers - application,
platform, virtualization, hardware, and co-location. Figure 12.1, modified from the
model presented in Rhoton (2010), shows these five tiers and their components.
SaaS enables users to leverage the service provider's applications running on a
cloud infrastructure. These applications cover a wide variety of domains and
functions, such as customer relationship management (CRM), email, billing and
financials, human resource management, backup and recovery, and content
management. The users can access these application services from various client
devices through a thin client interface like a web browser or mobile app. The users
do not manage or control the underlying cloud infrastructure of the service
provider, including servers, storage, operating systems, and network. The SaaS
model is an extension of the traditional application service provider (ASP) model,
in which software applications are hosted and managed in the ASP's system and are
accessible through a web browser or special client software provided by the ASP.
Nevertheless, ASPs focus on managing and hosting third-party software, whereas
SaaS service providers typically are also the developers of the software they host.