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and adapting VMs to the dynamics of a virtualization platform, which
leads to a better system coni guration management.
Coni guration languages, precompilers, and runtime systems have
been designed and implemented to support the DVM design and its
functionalities. The following section explains how VM modeling is sup-
ported in a DVM to provide services like coni guration and migration.
16.3.1 Virtual Machine Modeling
VM modeling addresses the problem of how to dei ne and describe a VM.
A prototype Knowledge Base repository is established with common
templates that are required by VM modeling. A DVM is described using
a Virtual Machine Description (VMD) script with the following informa-
tion: hardware, system identity, operating system, system coni guration,
software and their coni gurations, user data, and applications. A VMD
script is represented in two formats: a high-level representation and a
low-level representation. XML is used for the low-level representation.
Several high-level languages can be used for high-level representation.
Language used to describe/dei ne data grid is a choice of selection. It is
descriptive and thus users can easily understand as well as manually
create a script. The templates describe the resources and their coni gura-
tions. They also describe and enforce related software and hardware
dependencies. High-level description templates are used to represent a
DVM when communicating with a user or with a virtual environment
service and low-level representation of XML to represent a DVM during
DVM instantiation and migration. A compiler is used to translate a VMD
script in a high-level language into a script in XML. In this way, a VMD
script is sufi cient for DVM composition, instantiation, and migration.
Altogether, the templates (e.g., VMD scripts) form an extensible knowl-
edge base of hardware and software resources that may be referenced
when composing a DVM.
As shown in
Figure 16.4
,
a DVM script is separated into hierarchical
functional units. Each unit, such as hardware, software, network, and so
on, is dei ned with a template to describe its characteristics and coni gura-
tion. Figure 16.4 only shows the basic template structure. The Knowledge
Base repository is highly extensible and l exible. Third parties can contrib-
ute to the Knowledge Base. For instance, virtual computing environment
providers can dei ne their hardware templates specifying their own
policies. VM image service providers can provide more choices in operat-
ing systems and their coni guration by providing their own OS templates.
Software developers may support their software by providing a software
template that includes all the possible coni guration customization and
rules to coni gure them. The service providers also provide some fre-
quently used software templates to provide a starting point to a user; the
Knowledge Base is open to accept other templates. The user coni guration
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