Database introduction

Keeping everything in order

Think of a database as a sort of filing cabinet:a set of organised information. For example, a library archive. Whenever you arrange information you are building a database: your address book could be one.

In an electronic database the data are arranged in fields and records: normally fields are treated as as columns and records as rows, like in a spreadsheet.
A field is the heading for a category: in the case of our library, headings could be the Author's name, the Book's title, etc. Each field therefore contains data related to a given category. For example Alessandro Manzoni > I Promessi Sposi, or Umberto Eco > Il Nome della Rosa, could be the records. Once you feed data into the various fields you create records. Each record contains the information you want to add to your "filining cabinet". We may say that each record corresponds to a single library card in the library's catalogue.

The function of a database is to enhance fast and reliable search and retrieval of information.

If in a library with tousands of volumes we want to know if they have a certain book, we must query a database, and the result has to be certain. It's either yes or no: and if yes, we would probably also know where the book is, and if we can borrow it. All this information can be retrieved by searching the library cataloguing system. Chances are that it will be in the form of an electronic database.

Getting the information you want

Queries are the way users retrieve information. Typically, the user provides a string of characters, and after that the computer searches the database for a corresponding sequence. You can request, for example, all the records in which the contents of the field for a person's last name is the word "Rossi".

Even if there are many methods to implement searching and query functions, the SQL (Structured Query Language) is one of the most common. However, for most purposes, you needn't resort to this kind of programming language.

Different types of databases

Several different types of database management systems have been developed: flat, hierarchical, network, relational, and object-oriented.

Flat and relational databases are mostly utilised by individual users, but they are quite powerful tools nonetheless. The other types are primarily used by large businesses or organisations or for very special purposes. For example, when you use a search engine on the Internet, you actually send a query to a very large database that incorporates sophisticated searching functions. These databases do not reside on personal computers, which would have neither enough storing memory nor processing capabilities, but they are hosted on servers somewhere.

A flat database is a simple array of fields and records, something that can be easily handled by a spreadsheet. In a relational database different sets of flat databases are associated: a simple flat list becomes one row of a table, or "relation", and multiple relations can be associated to build a complex structure.

The information often consists of text. Number-oriented databases primarily contain information such as statistics, tables, financial data, etc. Small databases can be maintained on personal-computer systems and may be used by individuals at home or in a small company's office.

Some of the most typical commercial applications include airline reservation systems, production management functions, medical records in hospitals, and others. The largest databases are usually maintained by governmental agencies, business organisations, and universities.
Scientists, doctors, lawyers, financial analysts, stockbrokers, and researchers of all types increasingly rely on them for quick, selective access to large volumes of information.