Java Lec01

 What Is the World Wide Web?

• The internet is a network of computer networks worldwide
• The web is a tool used to retrieve information published on the internet
• To navigate the web we use a browser i.E. Netscape or internet explorer

Brief History of the www

• 1968 – DARPA (Defense Advanced Research Projects Agency) contracts with BBN (Bolt, Beranek & Newman) to create ARPAnet
• 1970 – First five nodes:
• UCLA
• Stanford
• UC Santa Barbara
• U of Utah, and
• BBN
• 1974 – TCP specification by Vint Cerf
• 1984 – On January 1, the Internet with its 1000 hosts converts en masse to using TCP/IP for its messaging.

HTTP/HTTPS

• Original web communication protocol
• Request-Response type
• Client (browser) will open a connection to a server and then send a request using a very specific format
• Server will respond and close the connection
• Stateless
• Does not maintain any connection information between transaction information
• Feature
• Negotiation of data representation.

TCP/IP

• Transmission Control Protocol over Internet Protocol
• IP ensures that data packets reach the destination from the source of communication
• Not necessarily data packets follow the same path
• TCP keeps track of these packets, and manages the assembling of these packets to form the original message
• Thus, both TCP and IP work together to ensure that effective transmission of data over the internet

Web Brochures vs. Web Applications

 

Goal	Information: Text, graphics, tables	Web interface to any application Interaction: Data entry, data selection, checking, ordering
Emphasis	Professional look, graphic design	Optimal support for the work flow
Implementation	Few interaction steps, mostly static pages (e.g. data entries) Navigation (browsing) – many integrated hyperlinks with jumps to other pages	Usually interacts with data source Incorporates business logic May contain simple or complex navigation Dynamic behavior.

	Web Brochures	Web Applications
Deployment	WWW	May present on companies LAN or WWW
Examples Apps	University Web Sites, Personal Home Page etc.	Amazon.com Purchasing System Address Book etc.

Advantages of Using Web Applications

• Allows you to browse a wide variety of internet sources
• Instantaneous connections to internet sites world wide

Disadvantages of Using Web Applications

• Connections can be slow or busy
• No standard methods of organization
• Out-of -date materials may not be removed
• Contents can be (maliciously) altered
• Sites can simply be moved/removed

Layers: Simplified view of application and its layers.

• It is important to note that the layers are merely logical groupings of the software components that make up the application or service.
• They help to differentiate between the different kinds of tasks performed by the components.
• The make it easier to design reusability into the solution.
• Each logical layer contains a number of discrete component types grouped into sublayers, with each sublayer performing a specific kind of task.
• By identifying the generic kinds of components that exist in most solutions, you can construct a meaningful map of an application or service, and then use this map as a blueprint for your design.

Evolution of Enterprise Application Framework

• Single tier
• Two tier
• Three tier
• N-Tier

Client-server architectures1-tier Architecture

• Entire application exists on single node
  • Installed on individual machines
• Dumb terminals are directly connected to mainframe
• Centralized model (as opposed distributed model)
  • Presentation, business logic, and data access are intertwined in one monolithic mainframe application
• Types of systems
  • Standalone executable
  • Mainframe applications

Client-server architectures 2-tier Architecture

• Client Server Applications
  • • The client and server can be heterogeneous
      • Different implementation languages
      • Different operating systems
• The roles can be transient
• Fat client – server only manages data
  • • • talk to back end database
      • SQL queries sent, raw data returned
      • Some Windows GUI based application
• Thin Client – server manages data and business logic
• Browser – server manages presentation too

Client-server architectures 2-tier Evaluation

Advantages

• Modifications on server propagated to clients
• Can distribute processing load
• Better scalability by adding server nodes and clients
• Database type independence

Disadvantages

• Client nodes require more computing power
• Development and maintenance more complex
• Presentation, data model, business logic are intertwined (at client side), difficult for updates and maintenance
• Data Model is “tightly coupled” to every client: If DB Schema changes, all clients break
• Updates have to be deployed to all clients making System maintenance nightmare
• DB connection for every client, thus difficult to scale
• Raw data transferred to client for processing causes high network traffic

3-tier Architecture (General)

Applications are generally partitioned as Client, Control (business) and Data Components

In 3-Tier Each logical partition maps to a layer in the system

• Modeling layers and software layers match 1-to-1
• Each layer implemented with appropriate technologies Layers have their own internal architectures

Advantages

• Complete separation of concerns
• Control logic can be reused by client applications
• Caches results in the controller layer
• Maximum flexibility for enterprise-wide applications

Disadvantages

• Difficult to integrate legacy stovepipes which represent large investment
• Complexity
• Speed decreases with levels of indirection and latency
• Increases cost and development time
• Lack of knowledgeable developers and managers

N-tier (multi-tier & multi-layered) Architecture

Layers added for better separation of concerns

• Every layer does a specified task, which improves cohesion and lowers coupling
• Application can be divided among developers with well defined roles.
• Layers and Tiers need not have 1-1 mapping. 3-tier is popular as its maps to typical IT problems
• For example a fortune five company uses
  • • JSP-Servlet-Handler-Translator-EJB-DAO layers
    • These layers are deployed on three physical tiers which are
    • Thin client à Web + Application server àDatabase Tiers

 

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