6 Database

A computer database is a structured collection of records or data that is stored in a computer system so that a computer program or person using a query language can consult it to answer queries.
The computer program used to manage and query a database is known as a database management system (DBMS).
Database systems have become an essential component of everyday life in modern society. In the course of a day, most of us encounter several activities that involve some interaction with a database. For example, if we go to the bank to deposit or withdraw fund; if reserving hotel, airline or train; if we access a computerized library catalogue or search for a bibliographic item. All of these our activities will involve someone accessing a database. Even purchasing items from the supermarket nowadays in many cases involves an automatic update of the database that keeps the inventory of supermarket items.

The ER model views the real world as a construct of entities and association between entities.

When we are designing our data model we have to fallow these steps bellow.

1. Design ER Model � Entity Relational model with its full attributes.
2. Convert ER Model into Relational model.
3. Then normalize to avoid the redundancy and constraints, if there is redundancy you should eliminated by using first normal form, second normal form and third normal form.

SQL:

SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database.

CREATE TABLE �customer�
(�customer_nr� Number PRIMARY KEY,
�firstname� text,
�lastname� text,
�tlf_nr� Number,
�address� text,
�post_nr� Number,
UNIQUE (customer_nr));

CREATE TABLE �order�
(�order_nr� AutoNumber PRIMARY KEY UNIQUE,
�customer_nr� Number,
UNIQUE (order_nr));

CREATE TABLE �order_line�
(�order_nr� AutoNumber PRIMARY KEY UNIQUE,
�ISBN� text,
�numbers� Number,
UNIQUE (order_nr));

CREATE TABLE �product�
(�ISBN� text PRIMARY KEY UNIQUE,
�price� Number,
�title� text,
�type� text,
�description� text,
UNIQUE (ISBN));

CREATE TABLE �city�
(�post_nr� Number PRIMARY KEY UNIQUE,
�city_name� text,
UNIQUE (post_nr));
INSERT INTO [order_line] (ISBN, numbers) Values (' " & ISBN.Text & "', '" & numbers.Text & " ')

INSERT INTO [order] (customer_nr) Values (' " & cust_nr.Text & " ')

Set Mail = Server.CreateObject("CDONTS.NewMail")
Mail.To = "books_order@fimus.dk"
Mail.From = "office@fimus.dk"
Mail.Subject = "New order"
Mail.Body = "Book IXBN.test ordered by fname.test lname.test address.test"
Mail.Send
Set Mail=nothing Very good dating site http://www.rus-women.com/

6.1 Normalization

Normalization is to check your database if there is a redundancy. Normalization is a design technique that is widely used as a guide in designing relational databases. Normalization is essentially a two steps process that puts data into tabular form by removing repeating groups and then removes duplicate data from the relation tables.

I have made some guidelines for ensuring that our database is being normalized. There are referred to as normal forms and numbered from one (the lowest form of normalization, referred to as first normal form (1NF)).
In practical applications, you will often see 1NF, 2NF and 3NF.

First normal form (1NF) is considered to be part of the formal definition of a relation, the basic relational model: historically it was defined to disallow multivolume attributes, composite attributes and their combinations.
The relational table, by definition, is in first normal form. All values of the columns are atomic, so they contain not repeating values.

Second Normal Form

A second normal form (2NF) is based on the concept of full functional dependency.
In order to be in second normal form, a relation must first fulfill the requirements to be in 1NF additionally, each no key attribute in the relation must be functionally dependent upon the primary key.

Third Normal Form

In order to be in third normal form (3NF), a relation must first fulfill the requirements to be in second normal form (2NF). Additionally, all attributes that are not dependent upon the primary key must be eliminated.

6.2 Relation model concept

The relational model represents the database as a collection of relations. When a relation is thought of as a table of values each row in the table represents a collection of related data values.