A compiler is a computer program that accepts programs written in high level language and produces an object program.

Differences between methods and constructors.

System calls provide the interface between a running program and the operating system. These calls are generally available as assembly- language instructions, and are usually listed in the manuals used by assembly-language programmers.

Some systems may allow system calls to be made directly from a higher-level language programm in which case the calls normally resemble predefined function or subroutine calls. They may generate a call to a special run-time routine that makes the system call, or the system call may be generated directly in-line.

DCL language is used to control access to data in a database.This language defines the access permissions for users and groups on the pieces of data in database.E.g We use commands to provide permissions for individual user to make SELECT statements for data table.

Examples of DCL commands include:

•     GRANT to allow specified users to perform specified tasks.
•     REVOKE to cancel previously granted or denied permissions.

The following privileges can be GRANTED TO or REVOKED FROM a user or role:

DML is used by computer programs database users to retrieve, insert, delete and update data in a database.Currently the most popular data manipulation language is that of SQL, which is used to retrieve and manipulate data in a Relational database.

Basic Data operations are:-

1. Select
2. Insert
3. Update
4. Delete

A Data Definition Language (DDL) is a computer language for defining data structures.In SQL, DDL contains commands for defining structure of data,altering and deleting structure of data.

1. Used to specify a database scheme as a set of definitions expressed in a DDL
2. DDL statements are compiled, resulting in a set of tables stored in a special file called a data dictionary or data directory.

    

    

SQL is a standard language for storing, manipulating, and retriving data stored in relational databases using a predefined language syntax and rules.SQL is widely used database language and provides  data manipulation (store, retrieve, update, delete) and database creation) with DataBase management Systems.

There are many types of DBMS(Database management Systems) available in market E.g: MS SQL Server, Microsoft Access, MSDE, Oracle, DB2, Sybase, MySQL, Postgres and Informix and they use SQL as standard database language.

The definition of a variable will assign storage for the variable and define the type of data that will be held in the location.

• Int
• Float
• Char
• Double

The three data types above have the following modifiers.

    * short
    * long
    * signed
    * unsigned

An array is a mean to store collection of values in a single variable. e.g instead of creating a separate variable to store each employee's name, you can use an array to store the names of all your employees in a single variable. This is how you would do it.

$employee_names[0] = "value1";
$employee_names[1] = 10;      //No matter of data type Wow..!
$employee_names[2] = "Susan";

SQL is a language used for accessing and manipulating databases by issuing queries(commands or request) for data.

basic operations for data base are INSERT,UPDATE,DELETE and SQL provide commands for each of these operations but SQL also provide others type of operations of DATABASES.

SQL can be divided into two parts:

1. Data Manipulation Language (DML)
2. Data Definition Language (DDL).