• The structure must support the functionality required of the system. Thus, the dynamic behavior of the system must be taken into account when designing the architecture.

• The structure--or architecture--must conform to the system qualities (also known as non-functional requirements). These likely include performance, security and reliability requirements associated with current functionality, as well as flexibility or extensibility requirements associated with accommodating future functionality at a reasonable cost of change.

• These requirements may conflict, and tradeoffs among alternatives are an essential part of designing an architecture. At the architectural level, all implementation details are hidden.

The steps in the software development are

        Requirement analysis ( problem statement)
        Object oriented analysis
        Architectural design
        Object oriented design
        Architectural design  (revisted)
        Object creation

Requirement analysis

This phase involves the domain specification of the software in need.

Example of a out come of this phase
A simple bookstore example as to be accessible from the web. The users would like to retrieve information regarding the books available in the company. Should be able to purchase books online using credit card transaction

Object oriented analysis

This phase involves the analysis of the domain. The requirement analysis sets the boundary for this phase.

Example of a out come of this phase
Develop the use case diagrams for all the business process
Develop the sequence diagrams.
Develop the class diagrams
Develop the collaboration diagrams.

Architectural design

This phase involves the architectural design for the software. The development of the architecture is based on the output of the Object oriented analysis. This phase tries to give a framework with in which all the components will work to satisfy all the customer requirements. This phase lays the outline of the system. Implementation details are not Documented at this phase.

An example of this phase would be

Decide and document the architecture
What framework will be used
J2EE / CORBA/ RMI / DCOM
Define any new hardware, software requirements.
Define how security will be handled
Define how performance is achieved
Define any bottlenecks
How to work out a practical solution with

• Security
• Performance
• Cost
• Reusing existing technology and business logic in the legacy system.
• Programmers

Object oriented design

In this phase the implementation design is done. Client tier whether it is an applet or HTML is decided. All the classes with hierarchy is defined. Design patterns if any are used. Object reuse is considered.

Architectural design ( revisited )

Any architectural considerations arising due to the detailed implementational design is discussed.

Example:
If the client uses HTML then the server side servlet can be communicated via HTTP without any modification in the existing systems.
If the client uses applet instead of HTML then consider HTTP tunneling on the server side is to be considered.

Object creation

The objects and code are implented.
 
 
 
 

Architecture Notation

UML, Unified Modeling Language by OMG , Object Management Group is the Architecture Notation.
 

Class diagram

A rectangle with three divisions for class name, attributes and methods
 
 
 

Sequence diagram
 
 

Basic Three-Tier Architecture

Three-Tier Architecture has three layers User Interface layer, business logic layer and the persistence layer.
The three tier software architecture emerged in the 1990s to overcome the limitations of the two tier architecture The third tier (middle tier server) is between the user interface (client) and the data management (server) components. This middle tier provides process management where business logic and rules are executed and can accommodate hundreds of users (as compared to only 100 users with the two tier architecture) by providing functions such as queuing, application execution, and database staging. The three tier architecture is used when an effective distributed client/server design is needed that provides (when compared to the two tier) increased performance , flexibility, maintainability, reusability, and scalability, while hiding the complexity of distributed processing from the user.
 
 

-Tier Architecture
The 3-tier architecture overcomes the weaknesses of the 2-tier and client/server architectures. It contains a client workstation, a component server, and a database server. The user interface is on the client side while business logic and data management are in dedicated tiers. Business logic resides on one machine where it can be easily managed.Successful implementation of a 3-tier architecture requires considerable applied experience.
 

n-Tier Architecture
The n-tier architecture is the same as the 3-tier architecture, but it has multiple (n) component and data management servers. It can distribute components across multiple servers and can access data in multiple databases. However, it requires careful planning of component interfaces to enable re-use and sharing.
 

Tier-to-Tier Communication
 

Communication between the user interface and business tiers can be achieved by	HTTP RMI Corba Dcom
Communication between the business and persistence tier can be achieved by	Jdbc IDL to Com bridge // check

HTTP

HTML forms based client interacts with the servlet on the server. Server interacts with the business layer and business layer interacts with the persistence layer.

RMI

This is a possible if the objects in the user interface and the business layers are all Java objects. The persistence layer is mostly accessed through JDBC. Other relational object mapping of the data layer is also possible.

Advantage of RMI
            Object are passed by value. The server/ client can reconstitute the objects easily.
            Data type can be any Java objects. Any Java objects can be passed as arguments.
            Arguments has to implement the serializable interface

Disadvantage of RMI
           Heterogeneous objects are not supported.

Corba
If the objects in the client layer and the business layer are heterogeneous, i.e. the objects are implemented in C, C++ Java, Smalltalk then Corba is most suitable.

Advantage of Corba
        Heterogeneous objects are supported.

Disadvantage of Corba
    Objects are not passed by value, only the argument data is passed.
    The server/ client has to reconstitute the objects with the data.
    Only commonly accepted data types can be passed as arguments.

Dcom
    This works best in windows environment.

Distributed Object Communication
 

	Advantages	Disadvantages
HTTP	Simple,  Established	Has to communicate to a Servlet, Java Server pages Cannot communicate to a Java class directly
RMI	Object are passed by value.  The server/ client can reconstitute the objects easily. Object are passed by reference Data type can be any Java objects.  Any Java objects can be passed as arguments. Arguments has to implement the  Serializable interface	Heterogeneous objects are not supported.
Corba	Heterogeneous objects are supported.	Objects are not passed by value, only the argument data is passed. The server/ client has to reconstitute the objects with the data. Only commonly accepted data types can be passed as arguments
Dcom	If windows is the deployment platform suits well with the operating system	This works in windows environment  at best

Distributed Object Frameworks

Distributed Object Frameworks are RMI, Corba, Dcom, EJB.
 
 

Basic Three-Tier Java Technology Architecture

The three-Tier Java Technology Architectureis achieved by HTML, Applet, Java Application on the client. Servlet, Java Server Pages on the Middle Tier. JDBC communication to the persistence or Database layer

RMI

// Explain later
 
 

Java IDL

// Explain later
 

Client	C to M comm.	Middle	M to P comm.	Persistence
HTML  HTML with applet	HTTP	Servlet Java Server Pages	JDBC	RDBMS Legacy File
Java Application	JRMP	RMI Server	JDBC	RDBMS Legacy File
Java Application	RMI- II0P	EJB	JDBC	RDBMS Legacy File
Java Application ( Not a Java 3 tier)	IIOP	Corba	JDBC	RDBMS Legacy File

 
 

Comparison of Three-Tier Communication Mechanisms
 
 
 
 

Review questions

• Where do the architectural design fit into the design phase

• What are the phases in ooad

• What is the requirement of a Java architect