Sunday, April 24, 2011

CrazyEngineers Forum - Computer Science & IT Engineering

CrazyEngineers Forum - Computer Science & IT Engineering

Different types of database languages

Posted: 23 Apr 2011 09:07 PM PDT

A database system provides two different types of languages: One to specify the database schema and other to express database queries and updates.

Data-definition Languages(DDL): A database schema is specified by a set of definitions expressed by a special language (DDL). The result of compilation of DDL statements is a set of tables that is stored in a special file called data dictionary or data directory.

A data dictionary is a file that contains metadata, that is data about data. This file is consulted before actual data are read or modified in the database system.
The storage structure and access methods used by the database system are specified by a set of definitions in a special type of DDL called as data storage and definition language. The result of compilation of these definitions is a set of instruction to specify the implementation details of the database schemas-Details are usually hidden from the user. Create table command is used for creation of the table. Suppose we wish to create table account having columns account_no, branch, and amount, then we have to write the following query;
create table account
(account_no number,
branch varchar2(50),
account number);
In this example, table account is created on which various modification operations can be performed.

Data manipulation language (DML): By data manipulation, we mean
1.The retrieval of information stored in the database
2.The insertion of new information into the database
3.Deletion of information from the database.
4.The modification of information stored in the database.
At the physical level, we must define algorithms that allow efficient access to data. At higher levels of abstraction, we emphasize ease of use. The goal is to provideefficient human interaction system.
A data manipulation language (DML) is a language that enables users to access or manipulate data organised by the appropriate data model. There are basically two types:

a) Procedural DMLs requires a user to specify what data are needed and how to get those data.

b)Non procedural DMLs Require a user to specify what data are needed without specifying how to get those data.

Non procedural DMLs are usually easier to learn and use than are procedural DMls. However since a user does not have to specify, how to get those data, these languages may generate code that may not be as that efficient as that produced by procedural languages.

For example: The simplest insert statement is a request to insert one tuple.
Suppose that we wish to insert the fact that there is an account A-9732 at a perryridge branch and that it has a balance of $1200. The query is

insert into account
values("A-9732", "Perryridge", 1200)
In this example, the values are specified in the order in which the corresponding attributes are listed in the relation schema.

Update your host file in windows to block all the pops

Posted: 23 Apr 2011 08:47 PM PDT

If you want to completely block all the unwanted connections like from adds ,pop ups then simply update your host file with below mentioned file


Download this file from here

C[lick here

After this it will completely block all the unwanted ads and connections made to your PC

linux : the complete reference

Posted: 23 Apr 2011 10:16 AM PDT

i will be happy if anyone mails me this Ebook at apoorvmunshi@gmail.com.
also can someone give me suggestion for a good linux boook? gonna buy one soon:cool::cool:

Java Collection

Posted: 23 Apr 2011 09:02 AM PDT

:confused::confused::confused::confused::confused: :confused::confused::confused::confused::confused: :confused::confused::confused:

Java Collections Does any one Know the basics of it , please explain in simple language !!

1) How list iterator differ from iterator ?
2)Why are seperate type Set and Sortedset Provided?
3)How does Java collection provide read only collection ?
4)What is purpose of Type map in Java Collection ?

help in programming

Posted: 23 Apr 2011 05:30 AM PDT

hello guys, I am making a project in which I have to display dates from calendar other than assigned dates and holidays( entered by user). Any idea how can it be done? I am working in .net framework
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