Week12-2. Networked Application Architecture Design and Implementation
Application software design and development is just one part of the computer system
development. To make the delivery to the clients application software is to be integrated into
technology infrastructure.
In general case Application Building Blocks are (ref. Figure 1):
- Application Software
- Data
- Infrastructure Software
- Local Area Network
- Server
- Desktop Computer
- Global Internet
Principal destiny of the networked application infrastructure is to support 4 most important
features:
- Communication across distance (LAN, Internet)
- Communication across time (Data storage)
- Computation and logic (Application software)
- Human-Computer Interface (Presentation, GUI)
The major Layers in a computer infrastructure are presented in the table
Layer
Application
Function
Provides specialized functionality directly
needed by a user
Example
GRP business logic
implementation
Application
components
Specialized modules incorporated by many
applications and purchased as a product from
an outside company
Middleware
Hides the heterogeneity and distribution of
operating system and network from the
application. Also provides capabilities useful
to a wide range of application, such as
scalability, performance, security
Manages and hides the details of resources
such as storage and printing. Also manages
the details of interhost communications
Provides communication of data from one
host to another
MQ Series – messages
services
CC Validation Connector
EntireX – connection to
legacy system (Adabas)
XML Parser
Transaction Services, ODBC
HTTP Server, Web
Application Server
Operating
System and
other Servers
Network
Windows, Unix
DBMS, Directory Services,
Mail Server
Novell, Windows based
network, Internet
The new terms explanation
Connector Objects – a special type of objects whose responsibility is to provide communication
between essentially different software components (for example developed on different
platforms)
Messages Services – a special middleware developed to mange messages effectively
Transaction Services – a special middleware to manage transactions to database
Directory Services – services that locate users, services and resources in the network
Network Infrastructure – provides services such as TCP/IP, directory and security whose
capabilities can be accessed via open, standard interfaces and protocols
Web (HTTP) Server provides communication over Internet
Application Server – a middleware to provide a scalability, performance and Security for
applications.
Mail Server – a middleware to provide e-mail services
Actually the choice what components should be included into the computer system model
depends on the factors listed below:
 Platform solution. So far 2 distinctly different platforms are known – Windows based
from Microsoft and Unix based from Java community. In spite of the possibility to
implement cross-platform solutions, there are the “native components” for each platform
allowing complete computer system modeling. Each platform offers fully integrated
solutions and each platform has its own advantages and disadvantages. Detailed
consideration of differences is beyond our course scope.
 Non-Functional Requirements, particularly scalability. The computer system scalability
is easier to achieve with Application Server included.
 Non-Functional Requirements, such as performance and security. To achieve higher level
of their implementation Directory Service, Transaction Services, Message Services
should be implemented using specialized software (Servers or middleware) instead of
those available with operating system.
 Data Storage Solution. Particularly the legacy system requires special components to be
integrated to the system.
 Functional Requirements. To implement some standard functions such as e-mail sending,
credit card validation, fax messaging it is preferable to use third party software
components instead of doing private development.
Application Architecture Examples
Big Enterprise Application Architecture (Fig. 3)
The model presents Java-based n-tier application architecture. It contains:
1. A browser interface access over TCP/IP network
2. Web Server
3. Application Server allows development and deployment of Java Applications and
provides a set of major services: State/Session management, Connection Management,
Load balancing and Logging
4. From Application Server there is the access to Transaction Management, Messages
Services, Data Servers and LDAP Directory. Application Server use JMS (Java Message
Services) to connect to MQ Series and JTS to connect to Transaction Services
5. Access to Data Server is provided through database middleware from Application Server
through Integration Tier. Data Servers could include legacy system.
6. Special Middleware is required to connect to legacy system.
7. LDAP Directory is accessible from Web Server and from Application Server
8. Mail Server is accessible from Application Server
Medium Enterprise Application Architecture (Fig. 4)
The model presents Java-based n-tier application architecture. However such components like
legacy system, Messages Services and Transaction Services are not included. Database Server is
Oracle. Messages and Transactions management is implemented by Application Server.
Small company application architecture (Fig. 5)
The model presents Java – 2-tier application. It does not use separate services and rely on
standard services of web servers and database servers. For this reason Web Server usually is
more functional to provide additional services, such as IIS or Apache
Network Topology
The network topology schema is to show physical implementation of computer system. This is
the blue print for deployment. Fig. 6 shows the example of topology for medium size application
Application Software Physical Implementation
The following tasks must be completed to arrange physical implementation of the application
software:
- Decide about EXE and DLL
- Decide about components (Compiling)
- Decide about component placement on the network (Deployment Diagram)
- Develop Start-Up procedure and configuration files/parameters
- Configure naming services
- Deployment on designated infrastructure
Executable code usually is compiled in one of 2 capacities;
- The exe module that is started by Start-Up procedure to initiate the system running.
Usually it contains the pieces of the software that is preferable to have constantly in
memory (Action Controller, Front Controller) because they are constantly in use. Very
often the main executable module is implemented as COM module or services of
operating system. They are included into the services that are under control of operating
system. EXE module creates its own process Client
- Dynamically Linked Libraries (DLL). The modules from the libraries are uploaded “by
request”, when some particular activity is initiated. Modules from DLL do not create
processes
A component is a physical model of code. Components can include both source code libraries
and runtime files. Components can be created in the correspondence to functional structure. A
component must have one or more interfaces. For example in GRP each mini-project can be
considered as a component. Components represent a physical perspective.
The component diagram is to define the dependency relationships between components, and this
is the only possible type of relationships. The component dependency relationships show the
order of compiling. If component A is dependent on B, B must be the first to compile.
Apart the order of compiling, other goal of component creating is to facilitate management and
interaction among teams involved into computer system development and implementation.
The deployment view represents physical deployment of the application. Deployment Diagram
shows all the nodes on the network, the connections between them, and the processes that will
run on each one. In other words, Deployment Diagram shows which components and objects run
on which node of application architecture. There is only one Deployment Diagram for a
particular application.
Start-Up procedure is essentially platform dependent. It could be simply a batch file with a single
command <cd c:\application/main.exe>. Or it could be the COM module activated once by
hands. Other detailed information about the application such as DLL names and paths,
parameters needed to link application to middleware or servers are sourced through
configuration files. In general terms configuration file could be considered as the link between
application software and middleware. Each middleware defines its configuration file format and
the only thing to do is to provide information requested. Configuration files language is either
scripts or nowadays very often XML format is in use. Start-Up procedure may provide the paths
to configuration files if they are not standard.
And finally it is important to take care about naming services configuration to link all the pieces.
Naming services provide the tool to support general requirements to object names availability.
The simple example of naming services is Registry. Commonly available Objects ID must be
included into the Registry. Another example – directory services. This is advanced storage of
objects names and connection for complicated networked application. One more example –
Domain Name Services (DNS) to store the URL of objects available via Internet.
Application Architecture Design
Application Architecture Design goal is to make the decision about each layer internal structure
and the ways of interaction (interfaces, integration). Non- Functional Requirements provide good
source of information to the architect. The table below contains the tasks that usually are to be
completed.
Task
Define platform
hardware
Define platform
software
Task description
Major sources of
information to
consider
To decide what kind of
Scale of the system,
machine shall be used as a commercial value,
server and as a client
potential number of
clients, performance
and security
requirements, other
non-functional
requirements
To decide what operating Platform hardware
system and languages will solution, functional
be used for development
requirements, nonand implementation.
functional requirements
Decide about DBMS
Define
communication
middleware
To define what kind of
communication software
is needed and decide what
is to be used
Platform hardware and
software, functional
requirements
Define Network
To define what software
Platform hardware and
Examples of
solutions
Servers: Sun Solaris
Clients: PC, Mac
Unix, Java, J2EE,
Oracle
Windows, VB, MS
SQL Server
Windows, VC++,
Oracle
Connection to DB –
ODBC, JDBC
Connection to Internet
– IIS, Apache, IBM
HTTP Server
OS embedded network
middleware
Define
application
components and
other
middleware
required
Define security
middleware and
hardware
Design the
system
architecture for
both
environments,
production and
QA
Define
configuration
parameters for
each
middleware
component
Design special
objects that may
be required to
implement
communication
shall be used to support
Local Area Network
To define what
components could be
purchased from a vendor
instead of in-house
developments. The
components are used to
implement some
functional requirements
such as e-mail sending, or
user’s authentication. Or
the necessity to have a
component could derive
from non-functional
requirements, such as
scalability, performance,
security
To define what additional
hardware/ software is
needed for the computer
system protection
Having the components
listed, design the exact
architecture. It means to
make the exact decision
about servers
configuration (how many,
the content of each),
where firewalls are
located, what is the
network topology.
Usually there are two
solutions – for production
and for QA
To define the
configuration parameters
values that make all the
components interact
smoothly.
In some special cases you
may be required to
develop special objects
needed to integrate
software components.
Example: legacy system
is to be included into a
new system architecture
software, nonfunctional requirements
Knowledge of
technologies available
from vendors,
Functional and nonfunctional
requirements,
Platform solutions
Platform solution
Non-functional
requirements
solutions
Novell
Web Application
Server – Web Sphere,
Web Logic.
E-mail Server – Post
Office, MS Exchange,
Domino.
Messages Service –
MQ Series.
Directory Service –
LDAP, Active
Directory
Naming Services –
Registry, JNDI
Firewalls,
Intrusion Detection
System,
Authentication tokens
Platform solution,
See the examples for a
middleware, additional big enterprise system
hardware, non(fig.2), middle size
functional requirements (fig. 3) and small
system (fig.4).
QA solution can be
more simple. Usually
it does not contain
additional middleware
and hardware, but it
must contain all the
components needed to
test functionality
Platform solution,
Usually the guides to
middleware, additional harden middleware
hardware, noncomponents are to be
functional
provided to the
requirements. Special
technical team
attention to security
requirements
Vendor’s information
Legacy system
Legacy system usually
interface, vendor’s
is developed on a
information, platform
mainframe, using
solution for the system powerful data storage
under development
like DB2 or Adabas.
The connectivity
middleware is usually
available from a
vendor, for example
Application
software
deployment
Decide about the
components and develop
Deployment Diagram
Class Diagrams,
platform solution,
functional requirements
EntireX for Adabas.
However project
specific components
are to be developed
and included into
application
architecture to
implement the
interface. Those
components are known
as adapters and
connectors objects.
Patterns are available
to design the objects
GRP Deployment
Diagram (Fig.6)