The SQL Language

The SQL language and relational database systems based on it are one of the most important foundation technologies in the computer industry today. Over the last decade, the popularity of SQL has exploded, and it stands today as the standard computer database language. Literally hundreds of database products now support SQL, running on computer systems from mainframes to personal computers and even handheld devices. An official international SQL standard has been adopted and expanded twice.
Virtually every major enterprise software product relies on SQL for its data management, and SQL is at the core of the database products from Microsoft and Oracle, two of the largest software companies in the world. From its obscure beginnings as an IBM research project, SQL has leaped to prominence as both an important computer technology and a powerful market force.

SQL is a tool for organizing, managing, and retrieving data stored by a computer database. The name "SQL" is an abbreviation for Structured Query Language. For historical reasons, SQL is usually pronounced "sequel," but the alternate pronunciation "S.Q.L." is also used. As the name implies, SQL is a computer language that you use to interact with a database. In fact, SQL works with one specific type of database, called a relational database.

The computer system in the figure has a database that stores important information. If the computer system is in a business, the database might store inventory, production, sales, or payroll data. On a personal computer, the database might store data about the checks you have written, lists of people and their phone numbers, or data extracted from a larger computer system. The computer program that controls the database is called a database management system, or DBMS.

When you need to retrieve data from a database, you use the SQL language to make the request. The DBMS processes the SQL request, retrieves the requested data, and returns it to you. This process of requesting data from a database and receiving back the results is called a database query—hence the name Structured Query Language.

The name Structured Query Language is actually somewhat of a misnomer. First of all, SQL is far more than a query tool, although that was its original purpose and retrieving data is still one of its most important functions. SQL is used to control all of the functions that a DBMS provides for its users, including: 

• Data definition. SQL lets a user define the structure and organization of the stored
data and relationships among the stored data items.

• Data retrieval. SQL allows a user or an application program to retrieve stored data
from the database and use it.

•Data manipulation. SQL allows a user or an application program to update the
database by adding new data, removing old data, and modifying previously stored
data.

• Access control. SQL can be used to restrict a user's ability to retrieve, add, and modify
data, protecting stored data against unauthorized access.

• Data sharing. SQL is used to coordinate data sharing by concurrent users, ensuring
that they do not interfere with one another.

• Data integrity. SQL defines integrity constraints in the database, protecting it from
corruption due to inconsistent updates or system failures.

SQL is thus a comprehensive language for controlling and interacting with a database management system. Second, SQL is not really a complete computer language like COBOL, C, C++, or Java.

SQL contains no IF statement for testing conditions, and no GOTO, DO, or FOR statements for program flow control. Instead, SQL is a database sublanguage, consisting of about forty statements specialized for database management tasks. These SQL statements can be embedded into another language, such as COBOL or C, to extend that language for use in database access. Alternatively, they can be explicitly sent to a database management system for processing, via a call level interface from a language such as C, C++, or Java.

Finally, SQL is not a particularly structured language, especially when compared to highly structured languages such as C, Pascal, or Java. Instead, SQL statements resemble English sentences, complete with "noise words" that don't add to the meaning of the statement but make it read more naturally. There are quite a few inconsistencies in the SQL language, and there are also some special rules to prevent you from constructing SQL statements that look perfectly legal, but don't make sense.

Source : Book "SQL: The Complete Reference"
by James R. Groff and Paul N. Weinberg 

Read More

What Is a Network?

A network is nothing more than two or more computers connected by a cable (or in some cases, by a wireless connection) so that they can exchange information. Of course, computers can exchange information in other ways besides networks. Most of us have used what computer nerds call the sneakernet. That’s where you copy a file to a diskette and then walk the disk over to someone
else’s computer. (The term sneakernet is typical of computer nerds’ feeble attempts at humor, and why not? As a way to transfer information, sneakernetwas pretty feeble.)


The whole problem with the sneakernet is that it’s slow — plus, it wears a trail in your carpet. One day, some penny-pinching computer geeks discovered that connecting computers together with cables was actually cheaper than replacing the carpet every six months. Thus the modern computer network
was born.

You can create a computer network by hooking all the computers in your office together with cables and installing a special network interface card (an electronic circuit card that goes inside your computer — ouch!) in each computer so you have a place to plug in the cable. Then you set up your computer’s


If you don’t want to mess with cables, you can create a wireless network instead. In a wireless network, each computer is equipped with a special wireless network adapter that has little rabbit-ear antennas. Thus, the computers can communicate with each other without the need for cables.

Computer networking has its own strange vocabulary. Fortunately, you don’t have to know every esoteric networking term. Here are a few basic buzzwords

1. to get you by: Networks are often called LANs. LAN is an acronym that stands for localarea
network. It’s the first TLA, or three-letter acronym, that you see in this
book. You don’t really need to remember it, or any of the many TLAs that
follow. In fact, the only three-letter acronym you need to remember is TLA.

2.You may guess that a four-letter acronym is called an FLA. Wrong! A fourletter
acronym is called an ETLA, which stands for extended three-letter
acronym. (After all, it just wouldn’t be right if the acronym for four-letter
acronym had only three letters.)

3. Every computer connected to the network is said to be on the network.
The technical term (which you can forget) for a computer that’s on the
network is a node.

4. When a computer is turned on and can access the network, the computer
is said to be online. When a computer can’t access the network, it’s offline.
A computer can be offline for several reasons. The computer can be
turned off, the user may have disabled the network connection, the
computer may be broken, the cable that connects it to the network can
be unplugged, or a wad of gum can be jammed into the disk drive.

5.When a computer is turned on and working properly, it’s said to be up.
When a computer is turned off, broken, or being serviced, it’s said to be
down. Turning off a computer is sometimes called taking it down. Turning
it back on is sometimes called bringing it up.


Source :
Book: "NetWorking For Dummies" by Doug Lowe

Read More

Manfaat Jaringan komputer

Ayo kita bersama-sama belajar pentingnya mengenal dan memahami manfaat jaringan komputer. Tanpa kita sadari ketika kita sedang di warnet atau pun internetan di kampus menggunakan hotspot, kita adalah penguna dari sebuah sistem jaringan komputer.


Timbul pertanyaan di benak kita seberapa pentingnya kah kita harus mempelajari jaringan komputer? Jawabannya tentu bisa kita lihat dari manfaat yang kita dapat dari sebuah jaringan komputer itu sendiri.


Jaringan komputer adalah kumpulan sejumlah peripheral yang terdiri dari beberapa perangkat komputer, prinet, LAN Card, dan peralatan lain yang saling terintegrasi satu sama lain. Nah, dengan demikian kita dapat saling tukar menukar data atau infomasi dengan mudah dan dalam Waktu tempo yang sesingkat-singkatnya eh.... dalam waktu singkat dan cepat.


Untuk sekedar pengetahuan rekan-rekan sekalian bahwasanya banyak sekali manfaat yang dapat kita peroleh apabila komputer kita terhubung dengan jaringan. Antara lain ialah:

· Dapat saling berbagi (Sharing) pemakaian file data dengan komputer teman kita.
· Tukar menukar data antar komputer dapat kita lakukan dengan super cepat.
· Memungkingkan kita dapat menggunakan sebuah printer yang terhubung dengan jaringan secara         bersama-sama dalam area jaringan. Contohnya seperti di warnet-warnet kawasan Indonesia dan sekitarnya.
· Lebih menghemat biaya.
· Efisiensi kerja menjadi meningkat.
· File-file data kita dapat lebih terpelihara dan dapat diproteksi.
· Kinerja sistem dapat kita tingkatkan sesuai dengan beban pemakaian komputer di jaringan. Kita hanya cukup menambah kemampuan processor jika membutuhkan peningkatan kinerja.

Mungkin itu beberapa dari sekian banyak sekali manfaat-manfaat yang dapat kita peroleh dari jaringan komputer.

Read More