Chapter 11 Physical Architecture layer design
Physical Architecture layer design
An important component of the design of an information system is the design of the physical
architecture layer, which describes the system’s hardware, software, and network environment.
A three tiered architecture uses three sets of computers.
The software on the client computer is responsible for presentation logic.
An application server(s) responsible for the application logic.
A separate database server(s) is responsible for data access logic and data storage.
N-tiered architecture uses more than three sets of computers.
The client is responsible for presentations.
A database server(s) is responsible for the data access logic and data storage.
The application logic is spread across two or more different sets of servers
The second component us a Web server that responds to the user’s requests, either by
providing (HTML) pages and graphics (application logic) or by sending the request to.
The third component (A set of twenty-eight programs written in the C programming language)
on another application server that performs various functions (application logic).
The fourth components are separate, making it easy to spread the different components on
different servers and to partition the application logic on two different servers.
The primary advantage of an N-tiered client-server architecture compared with two –tiered
architecture is that it separates out the processing that occurs to better balance the load on
different servers; it is more scalable.
Distributed objects computing
Distributed objects computing (DOC).
DOC represents a software layer that goes between clients and server hence it is known as
Middleware supports the interaction between objects in a distributed computing environment.
Ignore the peculiarities of a specific distributed environment.
Simply concentrate on the users, objects, and methods of an application instead of worrying
about which server contains which set of objects.
Physical location of the server object becomes irrelevant.
This can greatly reduce maintenance in a client-server environment
There are three competing approaches to support DOC: object management groups, Sun’s, and
Common object request broker (Cobra)
Sun supports DOC via its Enterprise JavaBeans (EJB) and its Java2 Enterprise Edition (J2EE).
Microsoft has its own competing approach to support DOC: the Distributed component object
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Cost of Infrastructure
One of the strongest driving forces to client-server architectures is cost of infrastructure
Personal computers are more than 1,000 times cheaper than mainframes for the same amount
of computing power
Therefore, the cost of client-server architectures is low compared to server-based architectures
that rely on mainframes.
Cost of Development
Developing application soft-ware for client-server computing is extremely complex, and most
experts believe that it costs four to five times more to develop and maintain application
software for client-server computing than it does for server-based computing.
Ease of Development
This backlog signals the difficulty in developing server-based systems.
Unfortunately, the applications for client-server can be very complex because they must be built
for server layers of hardware.
Today, most users of systems expect a graphics user interface (GUI).
GUI and web development tools typically are created to support client-based or client-server
application; rarely server-based environment support these types of applications.
Control and Security
Server-based architecture was originally developed to control and secure data and it is much
easier to administer because all of the data stored in a single location.
Client-server computing required a high degree of coordination among many components, and
the chance for security holes or control problems is much more likely
Scalability refers to the ability to increase or decrease the capacity of the computing
infrastructure in response to changing capacity needs.
Most scalable architecture is client-server computing because severs can be added to the
architecture when processing needs change.
Are used to represent the relationships between the hardware components used in the physical
infrastructure of an information system.
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A deployment diagram can be used to show the communication relationships among the
different nodes in the network.
The software components and how they are deployed over the physical architecture or
infrastructure of an information system.
A node represents any piece of hardware that needs to be included in the model of the physical
architecture layer design. For example, nodes typically include client computers, servers,
separate networks, or individual network devices.
A stereotype is modeled as a text item enclosed within <<>>.
Typical stereotypes include device, mobile device, database server, web server, and application
A node should include a set of typical network node symbols that can be used instead of the
Artefact represents a piece of the information system that is to be deployed onto the physical
architecture. Typically, an artefact represents a software component, a subsystem, a database
table, an entire database, or a layer.
A communication path represents a communication link between the nodes of the physical
architecture. Paths are stereotyped based on the type of communication link the represent e.g.
LAN, internet serial, parallel, or USB
The network model
The network model is a diagram that shows the major components of the information system
and their geographic locations through the organization.
To convey the complexity of the system and to show how the system’s software components
will fit together.
The diagram helps the project team develop the hardware and software specification that is
described later in this chapter.
Locations are the geographical sites related to these components.
Network model is created top-down whereby you first graphically depict all of the locations
where the application will reside
First, it shows the locations of the components that are needed to support the application.
Secondly step to the network model is to create low-level network diagrams for each of the
locations shown on the top-level diagram.
Low-level network models contain text descriptions below each of the hardware comments that
describe in detail the proposed hardware configurations and processing needs.
Primary purpose of the network model diagram is to present the proposed infrastructure for the
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Non-functional requirements and physical architecture layer design
Physical architecture layer specifies the overall architecture and the placement of