CLICK HERE FOR BLOGGER TEMPLATES AND MYSPACE LAYOUTS »

Tuesday, March 29, 2011

DATABASE

     DATABASE is a system intended to organize, store, and retrieve large amounts of data easily. It consists of an organized collection of data for one or more uses, typically in digital form. One way of classifying databases involves the type of their contents, for example: bibliographic, document-text, statistical. Digital databases are managed using database management systems, which store database contents, allowing data creation and maintenance, and search and other access.
      THE ADVANTAGES of database is Reduced data redundancy, Reduced updating errors and increased consistency, Greater data integrity and independence from applications programs, Improved data access to users through use of host and query languages, Improved data security, Reduced data entry, storage, and retrieval costs, Facilitated development of new applications program.
     THE DISADVANTAGES of database is Database systems are complex, difficult, and time-consuming to design, Substantial hardware and software start-up costs, Damage to database affects virtually all applications programs, Extensive conversion costs in moving form a file-based system to a database system, Initial training required for all programmers and users.


DATABASE MANAGEMENT SYSTEM


structure of DBMS:


DBMS (Database Management System) acts as an interface between the user and the database. The user requests the DBMS to perform various operations (insert, delete, update and retrieval) on the database. The components of DBMS perform these requested operations on the database and provide necessary data to the users. The various components of DBMS are shown below: 







1. DDL Compiler - Data Description Language compiler processes schema definitions specified in the DDL. It includes metadata information such as the name of the files, data items, storage details of each file, mapping information and constraints etc.
2. DML Compiler and Query optimizer - The DML commands such as insert, update, delete, retrieve from the application program are sent to the DML compiler for compilation into object code for database access. The object code is then optimized in the best way to execute a query by the query optimizer and then send to the data manager.
3. Data Manager - The Data Manager is the central software component of the DBMS also knows as Database Control System. 
The Main Functions Of Data Manager Are:
Convert operations in user's Queries coming from the application programs or combination of DML Compiler and Query optimizer which is known as Query Processor from user's logical view to physical file system, 
Controls DBMS information access that is stored on disk, 
It also controls handling buffers in main memory, 
 It also enforces constraints to maintain consistency and integrity of the data, 
It also synchronizes the simultaneous operations performed by the concurrent users, 
t also controls the backup and recovery operations.
4. Data Dictionary - Data Dictionary is a repository of description of data in the database. It contains information about 
Data - names of the tables, names of attributes of each table, length of attributes, and number of rows in each table,  Relationships between database transactions and data items referenced by them which is useful in determining which transactions are affected when certain data definitions are changed,  Constraints on data i.e. range of values permitted,  Detailed information on physical database design such as storage structure, access paths, files and record sizes,  Access Authorization - is the Description of database users their responsibilities and their access rights,  Usage statistics such as frequency of query and transactions.Data dictionary is used to actually control the data integrity, database operation and accuracy. It may be used as a important part of the DBMS.
5. Data Files - It contains the data portion of the database.
6. Compiled DML - The DML complier converts the high level Queries into low level file access commands known as compiled DML.
7. End Users -
DBMS MODEL
  • Hierarchical Model
-The hierarchical data model organizes data in a tree structure. There is a hierarchy of parent and child data segments.
-implies that a record can have repeating information, generally in the child data segments. Data in a series of records, which have a set of field values attached to it. It collects all the instances of a specific record together as a record type. These record types are the equivalent of tables in the relational model, and with the individual records being the equivalent of rows.
-example, an organization might store information about an employee, such as name, employee number, department, salary. The organization might also store information about an employee's children, such as name and date of birth. 

  • Network Model
- The popularity of the network data model coincided with the popularity of the hierarchical data model.
 - The basic data modeling construct in the network model is the set construct. A set consists of an owner record type, a set name, and a member record type. A member record type can have that role in more than one set, hence the multiparent concept is supported. An owner record type can also be a member or owner in another set. 
- The data model is a simple network, and link and intersection record types (called junction records by IDMS) may exist, as well as sets between them . Thus, the complete network of relationships is represented by several pairwise sets; in each set some (one) record type is owner (at the tail of the network arrow) and one or more record types are members (at the head of the relationship arrow). Usually, a set defines a 1:M relationship, although 1:1 is permitted. 
- The CODASYL network model is based on mathematical set theory

  • Relational Model
-  A database based on the relational model developed by E.F. Codd.
- allows the definition of data structures, storage and retrieval operations and integrity constraints. In such a database the data and relations between them are organised in tables. A table is a collection of records and each record in a table contains the same fields. 
- Certain fields may be designated as keys, which means that searches for specific values of that field will use indexing to speed them up. Where fields in two different tables take values from the same set, a join operation can be performed to select related records in the two tables by matching values in those fields. Often, but not always, the fields will have the same name in both tables.
-example, an "orders" table might contain (customer-ID, product-code) pairs and a "products" table might contain (product-code, price) pairs so to calculate a given customer's bill you would sum the prices of all products ordered by that customer by joining on the product-code fields of the two tables. This can be extended to joining multiple tables on multiple fields.
-  based on the Relational Algebra. 

  • Object-Oriented Model

    - add database functionality to object programming languages.bring much more than persistent storage of programming language objects.
    - extend the semantics of the C++, Smalltalk and Java object programming languages to provide full-featured database programming capability, while retaining native language compatibility. 
    - benefit of this approach is the unification of the application and database development into a seamless data model and language environment. As a result, applications require less code, use more natural data modeling, and code bases are easier to maintain. Object developers can write complete database applications with a modest amount of additional effort.
    - According to Rao (1994), "The object-oriented database (OODB) paradigm is the combination of object-oriented programming language (OOPL) systems and persistent systems. The power of the OODB comes from the seamless treatment of both persistent data, as found in databases, and transient data, as found in executing programs."




Sunday, March 20, 2011

What is Information Systems?

CHAPTER 11:INFORMATION SYSTEM

Definition of: information system 


A business application of the computer. It is made up of the database, application programs and manual and machine procedures. It also encompasses the computer systems that do the processing.

Processing the Data
The database stores the subjects of the business (master files) and its activities (transaction files). The application programs provide the data entry, updating, query and report processing.

The Procedures
The manual procedures document how data are obtained for input and how the system's output is distributed. Machine procedures instruct the computer how to perform scheduled activities, in which the output of one program is automatically fed into another.

Transaction Processing
The daily work is the online, interactive processing of the business transactions and updating of customer, inventory and vendor files (master files).

Batch Processing
At the end of the day or other period, programs print reports and update files that were not updated on a daily basis. Periodically, files must be updated for routine maintenance such as adding and deleting employees and making changes to product descriptions.See transaction processing.




Types of Information System


Categories of Information SystemCharacteristices
Transaction Processing System
Substitutes computer-based processing for manual procedures.

Deals with well-structured processes. Includes record keeping applications.
Management information system
Provides input to be used in the managerial decision process. Deals with supporting well structured decision situations. Typical information requirements can be anticipated.
Decision support system
Provides information to managers who must make judgements about particular situations. Supports decision-makers in situations that are not well structured.

Sunday, March 13, 2011

CHAPTER 10 PRIVACY & SECURITY

PRIVACY

Privacy is a concerns the collection and use of data about individuals. So, here is the three primary privacy issues to know:

1. Accuracy 
It is related to the responsibility of those who collect data to ensure that the data is correct.

2. Property
It is relates to who owns data and rights to software.

3.Access
It is relates to the responsibility of those who have data to control and who is able to use that data.

SPYWARE

Spyware is similar to a Trojan horse in that users unwittingly install the product when they install something else. A common way to become a victim of spyware is to download certain peer-to-peer file swapping products that are available today.

Aside from the questions of ethics and privacy, spyware steals from the user by using the computer's memory resources and also by eating bandwidth as it sends information back to the spyware's home base via the user's Internet connection. Because spyware is using memory and system resources, the applications running in the background can lead to system crashes or general system instability.

Because spyware exists as independent executable programs, they have the ability to monitor keystrokes, scan files on the hard drive, snoop other applications, such as chat programs or word processors, install other spyware programs, read cookies, change the default home page on the Web browser, consistently relaying this information back to the spyware author who will either use it for advertising/marketing purposes or sell the information to another party.

Licensing agreements that accompany software downloads sometimes warn the user that a spyware program will be installed along with the requested software, but the licensing agreements may not always be read completely because the notice of a spyware installation is often couched in obtuse, hard-to-read legal disclaimers.
      

Sunday, March 6, 2011

The Power of Social Networking is Infinite

Internet History

CHAPTER 9:COMMUNICATIONS & NETWORKS

Connectivity
Connectivity is the unbiased transport of packets between two end points. This is also the essential definition of "IP" (Internet Protocol). There is a strong boundary between the IP layer and the applications built upon it. TCP, for example, is an application protocol. In the term "TCP/IP" the slash emphasizes the separation of the two.

Communication systems


E-mail




















Instant Messaging






























Internet telephone












Electronic commerce

















Wireless revolution
Means in simple terms the replacement of wires used for communication , by wireless environment.For instance Local area network (LAN) has been replaced by WLAN ( Wireless LAN ) , similarly fixed line telephones have been replaced by Mobile hand sets including satellite handsets.

Networks
A network is a group of two or more computer systems linked together. There are many types of computer networks, including:

  • local-area networks (LANs) : The computers are geographically close together (that is, in the same building).


  • wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.


  • campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.


  • metropolitan-area networks MANs): A data network designed for a town or city.


  • home-area networks (HANs): A network contained within a user's home that connects a person's digital devices

  • Friday, March 4, 2011

    FUTURE DESIGNER LAPTOP: ROLLTOP

    The new future designer laptop name ROLLTOP. This design can make the user easy to bring it, lightweight and easy to use.
    enjoy this video to see how this new future design can make the user life more complex,comfortable  and easier when using this ROLLTOP

    Tuesday, March 1, 2011

    CHAPTER 8: STORAGE

    Storage is frequently used to mean the devices and data connected to the computer through input/output operations - that is, hard disk and tape systems and other forms of storage that don't include computer memory and other in-computer storage. For the enterprise, the options for this kind of storage are of much greater variety and expense than that related to memory.

    In a more formal usage, storage has been divided into: 
    ----->(1) primary storage, which holds data in memory (sometimes called random access         
                 memory or RAM) and other "built-in" devices such as the processor's L1 cache
    ----->(2) Secondary storage,which holds data on hard disks,tapes, and other devices requiring 
                input/output operations.


    DIFFERENCES BETWEEN PRIMARY AND SECONDARY STORAGE


    • All secondary storage is permanent
    • Most Primary Storage is temporary.
    • Secondary storage is usualy cheaper and large
    • Primary Storage is expensive and smaller.
    • Secondary Storage is bigger in capacity
    • Primary storage is smaller in capacity (L2 Cashe is only 2MB)
    • Seconday storage connects to the CPU via cables and therefore is slower
    • Primary storage is closer to the CPU and/or is intergrated onto it and thererfore is faster