database (access)

What is Microsoft Access.

We can define a Microsoft Access 2000 (the MS-Access or Access) as a system of relational databases, specifically designed for use under Windows 95/98. Consider the meaning of this definition, by describing its components.

What is a database

A database is a collection of information or data related to a particular topic. All who have worked in the archives of an office or consulting a book in a library, we know what a database "on paper", a suitable container (file) where you have a number of cards or sheets reviewed so that they can easily, and usually in a particular order (alphabetical, for example). Each of the cards contain information on a particular item (book, in the case of the library) which are entered in a predetermined and uniform for all of them (author, title, catalog number, topic, number of pages, publisher , date and place of printing, for example). However, the electronic database information is entered, stored and managed by computer programs, among whom Access, object of this course.

Databases and manual files

If we need to locate a book by its title, the cards are in the file alphabetically by title, we will not have to watch every one of the tabs to find it. But if what we want in that file are the books on a particular topic, we will need to review the whole file to find. Referring always to the file manually, could provide a solution to this problem by maintaining a copy of it sorted by subject, by another author, etc. So that we would require the tedious task of updating each of these files since they will a novelty.

Fields, records, tables and bases

A field is the smallest piece of information which comprises a base of data. This part contains a single indivisible data, such as price, size, name, etc..
The fields are arranged in series called records. A record is in electronic storage media, the equivalent of the card. Just as the tabs, each record is composed of the same fields and in the same provision is simply the content remain unchanged but the length and location of each of the data in all records. This collection of identical records in terms of their form in Access is grouped in what is called a table, which is equivalent to the container file or manual. For example, if the third field is the price of registration, all records will contain a table there, different numerical values for the price of each product or item.

The name table is due to their organization in the form of rows and columns.
Each row or line of data contains a single row, arranged side by side, so that, following down in each column we find a particular field of each record in the table. The field names that appear at the top of the table, containing information describing each of them, and serve as a means to reference the data in the field.

What does relational

This term refers to the way it organizes information Access to the various tables that compose a database. The figure below shows the implementation of a relational database system to a customer: We see that in the table of clients many of its fields are encoded, for example, the seller is replaced by the table by a customer number, which is then translated through table sales, the name that appears on the card ( gri sado-box we see in the bottom of the figure). Something similar happens with the province and category of VAT registration. The mechanism of the relationship is simple: just set the same (indicating which fields and which tables are involved) and then automatically have access to related data. For example, with reference to the figure, set the Category field to the table of categories VAT Vend field. Vendors to the table, etc..

Once the above relationships, every time you read a record in the table of customers, are positioned in place all the tables are related.

In the example, simply enter the customer number 249, the vendor table (in the examples loved Commission) will be positioned in "Mario" and the level of VAT on "Registered Resp. We can directly show the name of the vendor rather than your code, something similar happening with the VAT and the province level.
Develop a view of the customer file with all the necessary descriptions. Information obtained through the relationship shown in italics in the gray box of the figure, this type of view of the database will call consultation.

A relational database, finally, is a system specifically designed for the handling of information that has been previously organized in the form of one or more tables.

Creating a database

The first of the alternatives in the table of Figure 1.6 (previous lesson) is to create a new blank database, which is what we will do then.

1. Check the box corresponding to the first option: Access Database blank and click OK. Will now be presented the dialog in Figure 1.7, where we proposed to create a database named db1. This name is currently selected, which means that anything you type will replace the keyboard.

2. Changing the name proposed by a more adequate for our purposes, then write and practice hitting the Create button. Although the word "practice" has no accent is advisable to use it in any case in which we assign names to files, folders, Web addresses and e-mail, etc.., In this way to avoid confusion in future. After clicking Create will be presented on the screen of a window Access very important we work with throughout this course