Saturday, 15 June 2019

HTML Features, Advantages, Disadvantages

HTML stands for Hypertext Markup Language. It is used to display the document in the web browsers. HTML pages can be developed to be simple text or to be complex multimedia program containing sound, moving images and java applets. HTML is considered to be the global publishing format for Internet. It is not a programming language. HTML was developed by Tim Berners-Lee. HTML standards are created by a group of interested organizations called W3C (World Wide Web consortium). In HTML formatting is specified by using tags. A tag is a format name surrounded by angle brackets. End tags which switch a format off also contain a forward slash. Points to be remembered for HTML tags:

  1. Tags are delimited by angled brackets.
  2. They are not case sensitive
  3. If a browser not understands a tag it will usually ignore it.
  4. Some characters have to be replaced in the text by escape sequences.
  5. White spaces, tabs and newlines are ignored by the browser

Features of HTML

1) It is a very easy and simple language. It can be easily understood and modified.
2) It is very easy to make effective presentation with HTML because it has a lot of formatting tags.
3) It is a markup language so it provides a flexible way to design web pages along with the text.
4) It facilitates programmers to add link on the web pages (by html anchor tag) , so it enhances the interest of browsing of the user.
5) It is platform-independent because it can be displayed on any platform like Windows, Linux and Macintosh etc.
6) It facilitates the programmer to add Graphics, Videos, and Sound to the web pages which makes it more attractive and interactive.

Advantages of HTML:
1. First advantage it is widely used.
2. Every browser supports HTML language.
3. Easy to learn and use.
4. It is by default in every window so you don't need to purchase extra software.

Disadvantages of HTML:

1. It can create only static and plain pages so if we need dynamic pages then HTML is not useful.
2. Need to write lot of code for making simple webpage.
3. Security features are not good in HTML.

Situations Where DBMS is not necessary

It is also necessary to specify situations where it is not necessary to use a DBMS. If traditional file processing system is working well, and if it takes more money and time to design a database, it is better not to go for the DBMS. Moreover if only one person maintains the data and that person is not skilled in designing a database as well as not comfortable in using the DBMS then it is not advisable to go for DBMS.

DBMS is undesirable under following situations:
  1. DBMS is undesirable if the application is simple, well-defined, and not expected to change.
  2. Run time overheads are not feasible because of real-time requirements.
  3. Multiple accesses to data are not required.

Well, it isn’t necessary in a lot of places, but I will assume you are talking about information storage and access.

Wherever you do not expect concurrent access to the data and do not need simple structured access to parts of the data. Example: application’s local settings (like an .INI file). The application is the only editor and consumer of this data and typically it would need the whole structure at once, so just load the XML or JSON from the disk file into the in-memory structure and you are good to go. Although even then some vendors would use a SQLite database (call it DBMS or not is a call I’m not making now) to be able to address particular settings with a SQL expression.

I’m sure there are other good examples.

Applications that don’t need all of the data at once and data that needs concurrent access from multiple consumers almost always means DBMS. It is a pretty broad range, but there are also many DBMS in different shapes and flavors.


Component and Interfaces of DBMS

A database management system involves five major components: data, hardware,software, procedure, and users. These components and the interface between the components are shown in below figure 

Component and Interfaces of DBMS
1. Hardware

Hardware consists of a set of physical electronic devices such as computers (together with associated I/O devices like disk drives), storage devices, I/O channels, electromechanical devices that make interface between computers and the real world systems etc, and so on.

2. Software

The software includes the DBMS software, application programs together with the operating systems including the network software if the DBMS is being used over a network.

3. Data

Data in the database are raw facts. Useful information is retrieved from these raw facts. The main features of the data in the database are listed later:
  1. The data in the database is well organized (structured)
  2. The data in the database is related
  3. The data are accessible in different orders without great difficulty

The data in the database is persistent, integrated, structured, and shared

4. Procedures

Procedures refer to the instructions and rules that help to design the database and to use the DBMS. The users that operate and manage the DBMS require documented procedures on hot use or run the database management system. These may include.
  1. Procedure to install the new DBMS.
  2. To log on to the DBMS.
  3. To use the DBMS or application program.
  4. To make backup copies of database.
  5. To change the structure of database.
  6. To generate the reports of data retrieved from database.
5. People Interacting with Database

Here people refers to the people who manages the database, database administrator, people who design the application program, database designer and the people who interacts with the database, database users. A DBMS is typically run as a back-end server in a local or global network, offering services to clients directly or to Application Servers.

Peoples interacting with Database

5.1 Application Programmers

The people who write application programs in programming languages (such as Visual Basic, Java, or C++) to interact with databases are called Application Programmer.
5.2 Database Administrators 
A person who is responsible for managing the overall database management system is called database administrator or simply DBA.
5.3 End-Users
The end-users are the people who interact with database management system to perform different operations on database such as retrieving, updating, inserting, deleting data etc.

5.4 Database Designer

Database designer can be either logical database designer or physical database designer. 

  • Logical database designer is concerned with identifying the data, the relationships between the data, and the constraints on the data that is to be stored in the database.
  • The physical database designer takes the logical data model and decides the way in which it can be physically implemented.

5.5 Database Manager

Database manager is a program module which provides the interface between the low level data stored in the database and the application programs and queries submitted to the system.

6. Data Dictionary

A data dictionary, also known as a “system catalog,” is a centralized store of information about the database. It contains information about the tables, the fields the tables contain, data types, primary keys, indexes, the joins which have been established between those tables, referential integrity, cascades update, cascade delete, etc. This information stored in the data dictionary is called the “Metadata.”


The information (data) about the data in a database is called Metadata

7. Functional Components of Database System Structure

The functional components of database system structure are:
  1. Storage manager.
  2. Query processor.
1. Storage Manager

Storage manager is responsible for storing, retrieving, and updating data in the database. Storage manager components are:
  1. Authorization and integrity manager.
  2. Transaction manager.
  3. File manager.
  4. Buffer manager.

Authorization and Integrity Manager

Checks the integrity constraints and authority of users to access data.

Transaction Management

Transaction-management component ensures that the database remains in a consistent state despite system failures and transaction failure.

File Manager

File manager manages the allocation of space on disk storage. The file manager can:

– Create a file
– Delete a file
– Update the record in the file
– Retrieve a record from a file

Buffer Manager

Buffer manager is responsible for fetching data from disk storage into main memory.

2. Query processor:

The query processor transforms user queries into a series of low level instructions. It is used to interpret the online user's query and convert it into an efficient series of operations in a form capable of being sent to the run time data manager for execution. The query processor uses the data dictionary to find the structure of the relevant portion of the database and uses this information in modifying the query and preparing and optimal plan to access the database.


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