ഫോർ സ്ട്രോക്ക് പെട്രോൾ എഞ്ചിൻ - FOUR STROKE PETROL ENGINE

കംമ്പസറ്റിയൻ എഞ്ചിൻ - Internal Combustion Engine

Distributed Cooperative Caching In Social Wireless Networks,.

Distributed Cooperative Caching In Social Wireless Networks,.

WAP -WIRELESS APPLICATION PROTOCOL

The WAP Forum

In 1997, Ericsson, Motorola, Nokia, and Unwired Planet formed the WAP Forum(www.wapforum.org). More than 90 companies in the wireless telecommunications business are members of the WAP Forum. WAP is the standard developed by the WAP Forum, a consortium formed by device manufacturers, service providers, content providers, and  application providers. WAP specifies an application framework and protocols for wireless devices. WAP is a kind of fusion of mobile networking technologies and Internet technologies.

The WAP Forum’s objectives include :

·         To bring Internet content and advanced data services to digital cellular phones and  other wireless terminals.

·          To create an interoperable wireless protocol specification that will work across  differing wireless network technologies.

·          To enable the creation of content and applications that could scale across a wide range of wireless bearer networks and device types.

·         To embrace and extend existing standards and technologies

The key features provided by WAP include :

·         A programming model similar to the Internet

·         Wireless Markup Language(WML)

·         WML Script

·         Wireless Telephony Application(WTA)

·         Optimized protocol stack

The WAP architecture provides a scalable and extensible environment for application  development on mobile communication devices. It achieves this through a layered protocol design, covering protocols at Layer 4 and above. The WAP protocol stack is independent of the underlying network, which could take the form of GSM, CDMA, CDPD, iDEN, etc. Hence, WAP is essentially an application stack specification; it is not network-centric.

Wireless Application Environment(WAE)

Generally, WAE enables a spectrum of applications to be supported over WAP. WAE has two main elements, namely: (a) user agents, and (b) services and formats. The former includes the WML and WTA(Wireless Telephone Application) user agents. The latter consists of WML scripts, image formats, etc. A user agent can take the form of a Web browser. The WML user  agent is responsible for the interpretation of WML and WMLScript. WAP employs the same addressing model as in the Internet, that is, it use Uniformed Resource Locators(URLs). AURL uniquely identifies an available resource. WAP also uses Uniform Resource Identifiers (URIs) to address resources that are not accessed via well-known protocols.

Wireless Session Protocol(WSP)

The WSP provides both connection-oriented and connectionless services. It is optimized for low-bandwidth networks with relatively long latency. WSP is a binary version of HTTP version  1.1, but with the additions of : (a) session migrations, (b) header caching, etc. WAP connection mode allows the establishment of sessions between a client and the WAP gateway or proxy. It  can handle session interruptions as a result of mobility and reestablish session states at a later point in time. Header caching allows better bearer utilization since in HTTP, most of the  requests contain static headers that need to be re-sent again.

Wireless Transaction Protocol(WTP)

WTP is designed for transaction-style communications on wireless devices. In a transaction, users express their intentions and financial commitments to service providers for processing Very often, such transactions demand reliable, fast, and secure communications. WTP is a  lightweight protocol suitable for implementation in thin clients. WTP implements selective  retransmission of lost segments.

Wireless Transport Layer Security(WTLS)

WTLS is needed for WAP to ensure data integrity, privacy, authentication, and protection from denial-of-service. It is based on Transport Layer Security(TLS) 1.0, but optimized for  wireless channels. It provides transport layer security between a WAP client and the WAP gateway/proxy. Digital certificates are used for authentication and non repudiation of server and client. Encryption is also used to enhance the degree of confidentiality.

Wireless Datagram Protocol(WDP)

WDP is the transport layer protocol in WAP. It has the same functionality provided by the  Internet User Datagram Protocol(UDP). Whether WAP uses UDP or WDP, datagram delivery  services are provided by port number functionality and the characteristics of different beare services are hidden from the upper layers. WDP can be extended to provide segmentation and

reassembly functions

Integrity constraints

Entity Integrity

The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation. Having null value for the primary key implies that we cannot identify some tuples.This also specifies that there may not be any duplicate entries in primary key column key word

Referential Integrity

The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuples in the two relations. Informally, the referential integrity constraint states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation. It is a rule that maintains consistency among the rows of the two relations.

Domain Integrity\

The domain integrity states that every element from a relation should respect the type and restrictions of its corresponding attribute. A type can have a variable length which needs to be respected. Restrictions could be the range of values that the element can have, the default value if none is provided, and if the element can be NULL.

User Defined Integrity

A business rule is a statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business. E.g.: Age>=18 && Age<=60

 DBMS

a. Data:

·         It is a collection of information.

·         The facts that can be recorded and which have implicit meaning known as 'data'.

·         Example:

                 Customer  ----- 1.cname.

                                               2.cno.

                                               3.ccity.

b. Database:

·         It is a collection of interrelated data.

·         These can be stored in the form of tables.

·         A database can be of any size and varying complexity.

·         A database may be generated and manipulated manually or it may be computerized.

·         Example:

 Customer database consists the fields as cname, cno, and ccity

Cname	Cno	Ccity

c. Database System:

1.What are the advantages of a database system over conventional file processing systems? (8 Marks, April-2000)

·         It is computerized system, whose overall purpose is to maintain the information and to make that the information is available on demand.

·         Advantages:

                  1.Redundency can be reduced.

                  2.Inconsistency can be avoided.

                  3.Data can be shared.

                  4.Standards can be enforced.

                  5.Security restrictions can be applied.

                  6.Integrity can be maintained.

                  7.Data gathering can be possible.

                  8.Requirements can be balanced.

d. Database Management System (DBMS):

1.What are the advantages of DBMS over File processing systems?

                       

File Processing System:

·         It is a collection of interrelated data and programs to access the data.

·         It is a collection of programs that enables users to create and maintain a database.

·         It is a 'General Purpose Software System’ that facilitates the processes of Defining, Constructing and Manipulating databases for various applications.

·         Advantages:

1.Data Independence.

2.Efficient Data Access.

3.Data Integrity and security.

4.Data administration.

5.Concurrent access and Crash recovery.

6.Reduced Application Development Time.

·         Dis-advantages:

1.Data Redundancy.

2.Data Inconsistency.

3.Difficulty in accessing the data.

4.Data Isolation.

5.Security Problems.

LEVELS OF DATA ABSTRACTION 

 This is also called as 'The Three-Schema Architecture’, which can be used to separate the user applications and the physical database.

1.Physical Level:

·         This is a lowest level, which describes how the data is actually stores.

·         Example:

                        Customer account database can be described.

2.Logical Level:

·         This is next higher level that describes what data and what relationships in the database.

·         Example:     

               Each record

                       type customer = record

                                   cust_name: sting;

                                         cust_city: string;

                                         cust_street: string;

                              end;

3.Conceptual (view) Level:

·         This is a lowest level, which describes entire database.

·         Example:

                        All application programs.

                       

DATA MODELS

·         The entire structure of a database can be described using a data model.

·         A data model is a collection of conceptual tools for describing

·         Data models can be classified into following types.

1.Object Based Logical Models.

2.Record Based Logical Models.

3.Physical Models.

Explanation is as below.

1.Object Based Logical Models:

·         These models can be used in describing the data at the logical and view levels.

·         These models are having flexible structuring capabilities classified into following types.

a.       The entity-relationship model.

b.      The object-oriented model.

c.       The semantic data model.

d.      The functional data model.

2.Record Based Logical Models:

·                     These models can also be used in describing the data at the logical and view levels.

·                     These models can be used for both to specify the overall logical structure of the database and a higher-level description.

·                     These models can be classified into,

1.   Relational model.

2.   Network model.

3.      Hierarchal model.

3. Physical Models:

·         These models can be used in describing the data at the lowest level, i.e. physical level.

·         These models can be classified into

a.       Unifying model

b.      Frame memory model

.

5.Entity Relational Model (E-R Model)

                     The E-R model can be used to describe the data involved in a real world enterprise in terms of objects and their relationships.

Uses:

·                     These models can be used in database design.

·                     It provides useful concepts that allow us to move from an informal  

               description to precise description.

·                     This model was developed to facilitate database design by allowing the specification of overall logical structure of a database.

·                     It is extremely useful in mapping the meanings and interactions of real world enterprises onto a conceptual schema.

·                     These models can be used for the conceptual design of database

                  applications.

B2C and B2B Community Overview

B2C

 Large in number
 Users share an
experience
 Focus on low-touch
services
 Grows by mass adoption
 Forums, ratings and selfserve
offering
 Typically quick to scale
but users have weak ties
 Vague mission: it is
interpretive

B2B

 Number can vary
 Members share a purpose
 Focus on high-touch
services
 Grows by word of mouth
trust
 Programmatic
membership offering
 Typically slow to scale but
members have stronger
ties
 Strong stated mission
that is visibly embraced

E-Commerce Models

E-Commerce Models

•Business to consumer (B2C)

–Targets consumers or end users, and sells products and/or services

•Amazon.com, small business sites

•Business to business (B2B)

–Helps organizations to manage relationships and transactions with other businesses

•B2BExchange

•Consumer to consumer

–Not a traditional B2C model

•eBay

E-commerce security

E-commerce security

E-commerce Security is a part of the Information Security framework and is specifically applied to the components that affect e-commerce that include Computer Security, Data security and other wider realms of the Information Security framework.

Traditional Commerce

Traditional Commerce  vs. E-Commerce

•Similarities

–Both aim to deliver a valued product or service

–Both want to serve a large audience

–Both strive to quickly deliver products and services

•Differences

–E-commerce customers expect shorter fulfillment time

–E-commerce customers must understand Web-based technologies

–E-commerce provides a global audience

–E-commerce orders are processed without human interaction or travel to a store location

–E-commerce relies upon encryption for security

RDBMS=== LECTURE CLASS I

===========================================

1. What is DBMS? Explain its features.

====================================

A. In a typical file processing system, permanent records are stored in various files. A

number of different application programs are written to extract records from and add recordsto the appropriate files. But this method has a number of disadvantages, such as DataRedundancy, Difficulty in access, Data Isolation, Concurrent Access, Security Problems, andIntegrity Problems..

A Database Management System (DBMS) consists of a collection of interrelated data and a set of programs to access this data. This collection of Data is called Database. The Primary goal of a DBMS is to provide a convenient environment to retrieve and store database information.

Features of DBMS:-

=========================================

1.

The integration and sharing of data files minimizes the duplication and redundancy of

data to a great extent.

2.

Integration of data files also results in a considerable saving of storage space and in

data entry and data storage costs.

3.

Fewer application programs need to be developed for obtaining various reports due to independence of programs and data.

4.

The query language facility helps non-programming persons to access the database

for information as needed without the help of any programmer.

5.

Faster preparation of information to support non-recurring tasks and changing

conditions is possible.

6.

Updation of data becomes easier due to integration of data file. Fewer errors may

when several records may be updated simultaneously.

7.

Large database maintenance.

Software Engineering

Software Engineering is concerned with

•  Technical processes of software development
•  Software project management
•  Development of tools, methods and theories to support software production
•  Getting results of the required quality within the schedule and budget
•  Often involves making compromises
•  Often adopt a systematic and organized approach
•  Less formal development is particularly appropriate for the development of web-based systems

Software Engineering is important because

•  Individuals and society rely on advanced software systems
•  Produce reliable and trustworthy systems economically and quickly
•  Cheaper in the long run to use software engineering methods and techniques for softwaresystems

Fundamental activities being common to all software processes:

•  Software specification: customers and engineers define software that is to be produced and the constraints on its operation
•  Software development: software is designed and programmed
•  Software validation: software is checked to ensure that it is what the customer requires
•  Software evolution: software is modified to reflect changing customer and market requirements

Software Engineering is related to computer science and systems engineering:

 Computer science

o Concerned with theories and methods

 Software Engineering

o Practical problems of producing software

 Systems engineering

o Aspects of development and evolution of complex systems

o Specifying the system, defining its overall architecture, integrating the different parts to 

create the finished system

General issues that affect many different types of software:

 Heterogeneity

o Operate as distributed systems across networks

o Running on general-purpose computers and mobile phones

o Integrate new software with older legacy systems written in different programming 

languages

o Challenge: build dependable software that is flexible enough to cope with heterogeneity

 Business and social change

o Change existing software and rapidly develop new software

o Traditional software engineering techniques are time consuming

o Goal: reduce time to adapt to changing needs

 Security and trust

o Software is intertwined with all aspects of our lives

o See remote software systems (web page, web service interface)

o Make sure malicious users cannot attack software and information security is 

maintained

Essential attributes of good software

 Maintainability

 Dependability and security

 Efficiency

 Acceptability

Application types

 Stand-alone applications

 Interactive transaction-based applications

 Embedded control systems

 Batch processing systems

 Entertainment systems

 Systems for modeling and simulation

 Data collection systems