Databases

Data is best stored in a relational database format if it can include many instances of the same type of thing. Take a contact list, for instance. There are many contacts, all of whom potentially have the same types of information (address, phone number, etc.). Each "row" of data stores information about a different person, while each "column"

stores a specific attribute of each person: names in one column, addresses in another column, and home phone numbers in a third.

Android uses the SQLite database engine, a self-contained, transactional database engine that requires no separate server process. It is used by many applications and environments beyond Android, and is being actively developed by a large community.

The process that initiates a database operation, such as a SELECT or UPDATE, does the actual work of reading or writing the disk file that contains the database in order to fulfill the request. With SQLite, the database is a simple disk file. All of the data structures making up a relational database—tables, views, indexes, etc.—are within this file.

SQLite is not a Google project, although Google has contributed to it. SQLite has an international team of software developers who are dedicated to enhancing the software's capabilities and reliability. Some of those developers work full time on the project.

Reliability is a key feature of SQLite. More than half of the code in the project is devoted to testing the library. The library is designed to handle many kinds of system failures, such as low memory, disk errors, and power failures. In no case should the database be left in an unrecoverable state: this would be a showstopper on a mobile phone, where critical data is often stored in a database. If that database were susceptible to easy corruption, the mobile phone could become an expensive paperweight if the battery were to fail at an inopportune time.

This is not a book on SQL, so we will not go into much detail about the database commands themselves. Ample documentation about SQL in general and SQLite in particular can be found on the Web. But the SQL we use in our examples should be a good starting point for your own applications.

We'll use the MicroJobsDatabase.java file from our MicroJobs example application to discuss how to create and use a SQLite database using Android. This is the subject of the next section.

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