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21.1. What is a database?

A database is a file that is organized for storing data. Most databases are organized like a dictionary in the sense that they map from keys to values. The biggest difference is that the database is on disk (or other permanent storage), so it persists after the program ends. Because a database is stored on permanent storage, it can store far more data than a dictionary, which is limited to the size of the memory in the computer.

Like a dictionary, database software is designed to keep the inserting and accessing of data very fast, even for large amounts of data. Database software maintains its performance by building indexes as data is added to the database to allow the computer to jump quickly to a particular entry.

There are many different database systems which are used for a wide variety of purposes including: Oracle, MySQL, Microsoft SQL Server, PostgreSQL, and SQLite. We focus on SQLite in this book because it is a very common database and is already built into Python. SQLite is designed to be embedded into other applications to provide database support within the application. For example, the Firefox browser also uses the SQLite database internally as do many other products.

http://sqlite.org/

SQLite is well suited to some of the data manipulation problems that we see in Informatics such as the Twitter spidering application that we describe in this chapter.

Q-1: What is a database?

• Another name for a dictionary
• A database keeps it data after the program ends, while a dictionary only exists while a program is running.
• A list of lists
• That's a tuple!
• A file containing dictionaries
• While databases can have dictionaries as their stored data, it is not a requirement.
• A file that is organized for storing data
• A database is a file organized for storing data!

Q-3: Which database system are we using in this book?

• MySQL
• We are using a database system that uses Structured Query Language based syntax, but not MySQL.
• SQLite
• SQLite is designed to be embedded into other applications, so we're focusing on it in this book.
• Oracle
• Oracle is commonly used for running online transaction processing, data warehousing and mixed database workloads - not really what we're focusing on here.
• PostgreSQL
• We are using a database system that uses Structured Query Language based syntax, but not PostgreSQL.

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