XHTML

Introduction to XHTML

What You Should Already Know

Before you continue you should have a basic understanding of the following:

HTML and the basics of building web pages

If you want to study HTML first, please read our HTML tutorial.


What Is XHTML?

XHTML stands for EXtensible HyperText Markup Language

XHTML is almost identical to HTML 4.01

XHTML is a stricter and cleaner version of HTML

XHTML is HTML defined as an XML application

XHTML is a W3C Recommendation


XHTML is a W3C Recommendation

XHTML 1.0 became a W3C Recommendation January 26, 2000.

Stay updated with the latest W3C recommendations in our W3C tutorial.


All Browsers Support XHTML

XHTML is compatible with HTML 4.01. All browsers support XHTML

WHAT IS XHTML


Today we goonna learn about XHTML.XHTML is a stricter and cleaner version of HTML.
In this tutorial you will learn the difference between HTML and XHTML.

We will divide it in nine parts which are following:

1.XHTML INTRODUCTION

2.XHTML WHY

3.XHTML VS HTML

4.XHTML SYNTAX

5.XHTML DTD

6.XHTML HOW TO

7.XHTML VALIDATION

8.XHTML MODULES

9.XHTML SUMMARY

Server Manageability

Oracle Database is a sophisticated self-managing database that automatically monitors, adapts, and repairs itself. It automates routine DBA tasks and reduces the complexity of space, memory, and resource administration. Several advisors are provided to help you analyze specific objects. The advisors report on a variety of aspects of the object and describe recommended actions. Oracle Database proactively sends alerts when a problem is anticipated or when any of the user-selected metrics.

In addition to its self-managing features, Oracle Database provides utilities to help you move data in and out of the database.

This section describes these server manageability topics:

Automatic Manageability Features

Data Utilities

Automatic Manageability Features

Oracle Database has a self-management infrastructure that allows the database to learn about itself and use this information to adapt to workload variations and to automatically remedy any potential problem. This section discusses the automatic manageability features of Oracle Database.

Automatic Workload Repository

Automatic Workload Repository (AWR) is a built-in repository in every Oracle Database. At regular intervals, the database makes a snapshot of all its vital statistics and workload information and stores them in AWR. By default, the snapshots are made every 60 minutes, but you can change this frequency. The snapshots are stored in the AWR for a period of time (seven days by default) after which they are automatically purged.

See Also:

Oracle Database Concepts and Oracle Database 2 Day DBA for overviews of the Automatic Workload Repository

Oracle Database Performance Tuning Guide for details on using Automatic Workload Repository for statistics collection

Automatic Maintenance Tasks

Oracle Database uses the information stored in AWR to identify the need to perform routine maintenance tasks, such as optimizer statistics refresh and rebuilding indexes. Then the database uses the Scheduler to run such tasks in a predefined maintenance window.

See Also:

Oracle Database Concepts for an overview of the maintenance window

Chapter 23, "Managing Automatic System Tasks Using the Maintenance Window" for detailed information on using the predefined maintenance window

Server-Generated Alerts

Some problems cannot be resolved automatically and require the database administrator's attention. For these problems, such as space shortage, Oracle Database provides server-generated alerts to notify you when then problem arises. The alerts also provide recommendations on how to resolve the problem.

See Also:"Server-Generated Alerts" in this book for detailed information on using APIs to administer server-generated alerts

Advisors

Oracle Database provides advisors to help you optimize a number of subsystems in the database. An advisory framework ensures consistency in the way in which advisors are invoked and results are reported. The advisors are use primarily by the database to optimize its own performance. However, they can also be invoked by administrators to get more insight into the functioning of a particular subcomponent.

See Also:
Oracle Database Concepts for an overview of the advisors

Oracle Database 2 Day DBA for more detailed information on using the advisors

Data Utilities

Several utilities are available to help you maintain the data in your Oracle Database. This section introduces two of these utilities:

SQL*Loader

Export and Import Utilities

See Also:

Oracle Database Utilities for detailed information about these utilities

SQL*Loader

SQL*Loader is used both by database administrators and by other users of Oracle Database. It loads data from standard operating system files (such as, files in text or C data format) into database tables.

Export and Import Utilities

Oracle export and import utilities enable you to move existing data in Oracle format between one Oracle Database and another. For example, export files can archive database data or move data among different databases that run on the same or different operating systems.

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Creating and Maintaining a Password File

You can create a password file using the password file creation utility, ORAPWD. For some operating systems, you can create this file as part of your standard installation.

This section contains the following topics:

Using ORAPWD

Setting REMOTE_LOGIN_ PASSWORDFILE

Adding Users to a Password File

Maintaining a Password File


Using ORAPWD

When you invoke this password file creation utility without supplying any parameters, you receive a message indicating the proper use of the command as shown in the following sample output:

> orapwd
Usage: orapwd file= password= entries= force=

where

file - name of password file (mand),
password - password for SYS (mand),
entries - maximum number of distinct DBAs and OPERs (opt),
force - whether to overwrite existing file (opt)
There are no spaces around the equal-to (=) character.

The following command creates a password file named acct.pwd that allows up to 30 privileged users with different passwords. In this example, the file is initially created with the password secret for users connecting as SYS.

orapwd FILE=acct.pwd PASSWORD=secret ENTRIES=30

The parameters in the ORAPWD utility are described in the sections that follow.


FILE

This parameter sets the name of the password file being created. You must specify the full path name for the file. The contents of this file are encrypted, and the file cannot be read directly. This parameter is mandatory.

The types of filenames allowed for the password file are operating system specific. Some operating systems require the password file to adhere to a specific format and be located in a specific directory. Other operating systems allow the use of environment variables to specify the name and location of the password file. For name and location information for the Unix and Linux operating systems, see Administrator's Reference for UNIX-Based Operating Systems. For Windows, see Platform Guide for Microsoft Windows. For other operating systems, see your operating system documentation.

If you are running multiple instances of Oracle Database using Oracle Real Application Clusters, the environment variable for each instance should point to the same password file.

Caution:

It is critically important to the security of your system that you protect your password file and the environment variables that identify the location of the password file. Any user with access to these could potentially compromise the security of the connection.

PASSWORD

This parameter sets the password for user SYS. If you issue the ALTER USER statement to change the password for SYS after connecting to the database, both the password stored in the data dictionary and the password stored in the password file are updated. This parameter is mandatory.

Note:

You cannot change the password for SYS if REMOTE_LOGIN_PASSWORDFILE is set to SHARED. An error message is issued if you attempt to do so.

ENTRIES

This parameter specifies the number of entries that you require the password file to accept. This number corresponds to the number of distinct users allowed to connect to the database as SYSDBA or SYSOPER. The actual number of allowable entries can be higher than the number of users, because the ORAPWD utility continues to assign password entries until an operating system block is filled. For example, if your operating system block size is 512 bytes, it holds four password entries. The number of password entries allocated is always a multiple of four.

Entries can be reused as users are added to and removed from the password file. If you intend to specify REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE, and to allow the granting of SYSDBA and SYSOPER privileges to users, this parameter is required.

Caution:

When you exceed the allocated number of password entries, you must create a new password file. To avoid this necessity, allocate a number of entries that is larger than you think you will ever need.

FORCE

This parameter, if set to Y, enables you to overwrite an existing password file.An error is returned if a password file of the same name already exists and this parameter is omitted or set to N.

Setting REMOTE_LOGIN_ PASSWORDFILE

In addition to creating the password file, you must also set the initialization parameter REMOTE_LOGIN_PASSWORDFILE to the appropriate value. The values recognized are:

1.NONE: Setting this parameter to NONE causes Oracle Database to behave as if the password file does not exist. That is, no privileged connections are allowed over nonsecure connections.

2.EXCLUSIVE: (The default) An EXCLUSIVE password file can be used with only one instance of one database. Only an EXCLUSIVE file can be modified. Using an EXCLUSIVE password file enables you to add, modify, and delete users. It also enables you to change the SYS password with the ALTER USER command.

3.SHARED: A SHARED password file can be used by multiple databases running on the same server, or multiple instances of a Real Application Clusters (RAC) database. A SHARED password file cannot be modified. This means that you cannot add users to a SHARED password file. Any attempt to do so or to change the password of SYS or other users with the SYSDBA or SYSOPER privileges generates an error. All users needing SYSDBA or SYSOPER system privileges must be added to the password file when REMOTE_LOGIN_PASSWORDFILE is set to EXCLUSIVE. After all users are added, you can change REMOTE_LOGIN_PASSWORDFILE to SHARED, and then share the file.

This option is useful if you are administering multiple databases or a RAC database.

If REMOTE_LOGIN_PASSWORDFILE is set to EXCLUSIVE or SHARED and the password file is missing, this is equivalent to setting REMOTE_LOGIN_PASSWORDFILE to NONE.

Adding Users to a Password File

When you grant SYSDBA or SYSOPER privileges to a user, that user's name and privilege information are added to the password file. If the server does not have an EXCLUSIVE password file (that is, if the initialization parameter REMOTE_LOGIN_PASSWORDFILE is NONE or SHARED, or the password file is missing), Oracle Database issues an error if you attempt to grant these privileges.

A user's name remains in the password file only as long as that user has at least one of these two privileges. If you revoke both of these privileges, Oracle Database removes the user from the password file.

Creating a Password File and Adding New Users to It

Use the following procedure to create a password and add new users to it:

1.Follow the instructions for creating a password file as explained in "Using ORAPWD".

2.Set the REMOTE_LOGIN_PASSWORDFILE initialization parameter to EXCLUSIVE. (This is the default.)

Note:

REMOTE_LOGIN_PASSWORDFILE is a static initialization parameter and therefore cannot be changed without restarting the database.

3.Connect with SYSDBA privileges as shown in the following example:

CONNECT SYS/password AS SYSDBA

4.Start up the instance and create the database if necessary, or mount and open an existing database.

5.Create users as necessary. Grant SYSDBA or SYSOPER privileges to yourself and other users as appropriate. See "Granting and Revoking SYSDBA and SYSOPER Privileges", later in this section.

Granting and Revoking SYSDBA and SYSOPER Privileges
If your server is using an EXCLUSIVE password file, use the GRANT statement to grant the SYSDBA or SYSOPER system privilege to a user, as shown in the following example:


GRANT SYSDBA TO oe;


Use the REVOKE statement to revoke the SYSDBA or SYSOPER system privilege from a user, as shown in the following example:

REVOKE SYSDBA FROM oe;

Because SYSDBA and SYSOPER are the most powerful database privileges, the WITH ADMIN OPTION is not used in the GRANT statement. That is, the grantee cannot in turn grant the SYSDBA or SYSOPER privilege to another user. Only a user currently connected as SYSDBA can grant or revoke another user's SYSDBA or SYSOPER system privileges. These privileges cannot be granted to roles, because roles are available only after database startup. Do not confuse the SYSDBA and SYSOPER database privileges with operating system roles.

See Also:

Oracle Database Security Guide for more information on system privileges

Viewing Password File Members

Use the V$PWFILE_USERS view to see the users who have been granted SYSDBA or SYSOPER system privileges for a database. The columns displayed by this view are as follows:

Column Description

USERNAME This column contains the name of the user that is recognized by the password file.

SYSDBA If the value of this column is TRUE, then the user can log on with SYSDBA system privileges.

SYSOPER If the value of this column is TRUE, then the user can log on with SYSOPER system privileges.

Maintaining a Password File

This section describes how to:

1.Expand the number of password file users if the password file becomes full

2.Remove the password file

Expanding the Number of Password File Users

If you receive the file full error (ORA-1996) when you try to grant SYSDBA or SYSOPER system privileges to a user, you must create a larger password file and regrant the privileges to the users.

Replacing a Password File

Use the following procedure to replace a password file:

1.Identify the users who have SYSDBA or SYSOPER privileges by querying the V$PWFILE_USERS view.

2.Delete the existing password file.

3.Follow the instructions for creating a new password file using the ORAPWD utility in "Using ORAPWD". Ensure that the ENTRIES parameter is set to a number larger than you think you will ever need.

4.Follow the instructions in "Adding Users to a Password File".

Removing a Password File

If you determine that you no longer require a password file to authenticate users, you can delete the password file and then optionally reset the REMOTE_LOGIN_PASSWORDFILE initialization parameter to NONE. After you remove this file, only those users who can be authenticated by the operating system can perform SYSDBA or SYSOPER database administration operations.