Information Technology Reference
In-Depth Information
sential system properties, such as resource consumption, fault tolerance or
persistence. These groupings (illustrated in a much simplified configuration
in figure 5.1), include such elements as nodes and, within them, sets of clus-
ters, with cluster managers, sets of capsules, with capsule managers, and a
nucleus.
These concepts are used to define the logical structure of the node. These
days, there are many complete packages of infrastructure support available,
but it is still important to have a common functional architecture for the infras-
tructure to support interoperation and interworking between these products,
or to extend it to new technologies as they appear.
It is important to understand the kinds of functionality required to sup-
port provision of distribution transparencies, the basic mechanisms needed to
achieve those functionalities, and how they can be structured and assigned
to the architectural elements of the engineering viewpoint. This provides a
reference architecture, against which existing distributed processing systems
can be compared and evaluated, or with which tomorrow's systems can be
designed. Using it helps technical architects specify or select required infras-
tructure characteristics.
The first two concepts make the distinction between provision and use of
resources, as follows:
A node represents a physical object that has computing, communication
and storage capabilities, and generally has connections to other nodes. A
node will therefore have one or more network addresses, and the elements
deployed on the node can become network accessible. Your laptop, your
oce PC, your mobile phone and your organization's server machines
are all nodes. However, this is a slight simplification because a node
does not actually have to be a separate, physically tangible object; a
virtualization of such a resource (see section 9.1) can also be considered
to be a node.
An engineering object is any object of interest in this viewpoint.
These objects support computational requirements, distribution trans-
parencies or infrastructural aspects of the system. We distinguish here
between BEOs, which represent computational objects, and other en-
gineering objects, whose aim is to provide basic engineering functions,
such as managers, interceptors and directories.
The engineering viewpoint language also defines three other concepts that
describe the principal controlling elements involved in any engineering speci-
fication:
A nucleus represents the basic mechanisms needed to make a node
function at the lowest level, typically representing an operating system
kernel that manages and allocates processing capabilities, communica-
tion capabilities and storage capabilities. Fair scheduling and accurate
