SQLite

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SQLite
SQLite370.svg
Developer(s) D. Richard Hipp
Initial release August 2000 (2000-08)
Stable release 3.7.17 / May 20, 2013; 24 days ago (2013-05-20)
Written in C
Operating system Cross-platform
Size ~350 KiB
Type RDBMS (embedded)
License Public domain[1]
Website sqlite.org

SQLite (/ˌɛskjuːɛlˈlaɪt/[2] or /ˈsiːkwɛl.laɪt/)[3] is a relational database management system contained in a small (~350 KB)[4] C programming library. In contrast to other database management systems, SQLite is not a separate process that is accessed from the client application, but an integral part of it.

SQLite is ACID-compliant and implements most of the SQL standard, using a dynamically and weakly typed SQL syntax that does not guarantee the domain integrity.

SQLite is a popular choice as embedded database for local/client storage in application software such as web browsers. It is arguably the most widely deployed database engine, as it is used today by several widespread browsers, operating systems, and embedded systems, among others.[5] SQLite has many bindings to programming languages.

The source code for SQLite is in the public domain.[1][6]

Contents

Design[edit]

Unlike client–server database management systems, the SQLite engine has no standalone processes with which the application program communicates. Instead, the SQLite library is linked in and thus becomes an integral part of the application program. (In this, SQLite follows the precedent of Informix SE of c. 1984) The library can also be called dynamically. The application program uses SQLite's functionality through simple function calls, which reduce latency in database access: function calls within a single process are more efficient than inter-process communication. SQLite stores the entire database (definitions, tables, indices, and the data itself) as a single cross-platform file on a host machine. It implements this simple design by locking the entire database file during writing. SQLite read operations can be multitasked, though writes can only be performed sequentially.

History[edit]

D. Richard Hipp designed SQLite in the spring of 2000 while working for General Dynamics on contract with the United States Navy.[7] Hipp was designing software used on board guided missile destroyers, which were originally based on HP-UX with an IBM Informix database back-end. The design goals of SQLite were to allow the program to be operated without installing a database management system or requiring a database administrator. In August 2000, version 1.0 of SQLite was released, based on gdbm (GNU Database Manager). SQLite 2.0 replaced gdbm with a custom B-tree implementation, adding support for transactions. SQLite 3.0, partially funded by America Online, added internationalization, manifest typing, and other major improvements.

In 2011 Hipp announced his plans to add an UnQL interface to SQLite databases and to develop UnQLite, an embeddable document-oriented database.[8] Howard Chu ported SQLite 3.7.7.1 to use Openldap MDB instead of the original Btree code and called it sqlightning. One cited insert test of 1000 records was 20 times as fast.[9][10]

Features[edit]

SQLite implements most of the SQL-92 standard for SQL but it lacks some features. For example it has partial support for triggers, and it can't write to views (however it supports INSTEAD OF triggers that provide this functionality). While it supports complex queries, it still has limited ALTER TABLE support, as it can't modify or delete columns.[11]

SQLite uses an unusual type system for an SQL-compatible DBMS. Instead of assigning a type to a column as in most SQL database systems, types are assigned to individual values; in language terms it is dynamically typed. Moreover, it is weakly typed in some of the same ways that Perl is: one can insert a string into an integer column (although SQLite will try to convert the string to an integer first, if the column's preferred type is integer). This adds flexibility to columns, especially when bound to a dynamically typed scripting language. However, the technique is not portable to other SQL products. A common criticism is that SQLite's type system lacks the data integrity mechanism provided by statically typed columns in other products. The SQLite web site describes a "strict affinity" mode, but this feature has not yet been added.[12] However, it can be implemented with constraints like CHECK(typeof(x)='integer').[7]

Several computer processes or threads may access the same database concurrently. Several read accesses can be satisfied in parallel. A write access can only be satisfied if no other accesses are currently being serviced. Otherwise, the write access fails with an error code (or can automatically be retried until a configurable timeout expires). This concurrent access situation would change when dealing with temporary tables. This restriction is relaxed in version 3.7 when WAL is turned on enabling concurrent reads and writes.[13]

A standalone program called sqlite3 is provided that can be used to create a database, define tables within it, insert and change rows, run queries and manage an SQLite database file. This program is a single executable file on the host machine. It also serves as an example for writing applications that use the SQLite library.

SQLite is a popular choice for local/client SQL storage within a web browser and within a rich internet application framework;[14] most notably the leaders in this area (Google Gears,[15] Adobe AIR,[16] and Firefox[17]) embed SQLite.

SQLite full Unicode support is optional.[18]

SQLite also has bindings for a large number of programming languages, including BASIC, C, C++, Clipper//Harbour, Common Lisp, C#, Curl, D, Delphi, Free Pascal, Haskell, Java, Livecode, Lua, newLisp, Objective-C (on OS X and iOS), OCaml, Perl,[19] PHP, Pike, Python,[20] REBOL, R, REALbasic, Ruby,[21] Scheme, Smalltalk, Tcl, Visual Basic, and JavaScript.[22] An ADO.NET adapter, initially developed by Robert Simpson, is maintained jointly with the SQLite developers since April 2010.[23] An ODBC driver has been developed and is maintained separately by Christian Werner.[24] Werner's ODBC driver is the recommend connection method for accessing SQLite from OpenOffice.[25] There is also a COM (ActiveX) wrapper making SQLite accessible on Windows to scripted languages such as JScript and VBScript. This adds database capabilities to HTML Applications (HTA).[26]

SQLite has automated regression testing prior to each release.[27] Over 2 million tests are run as part of a release's verification. Starting with the August 10, 2009 release of SQLite 3.6.17, SQLite releases have 100% branch test coverage, one of the components of code coverage.

Development[edit]

SQLite development stores revisions of its source code in Fossil, a distributed version control system that is itself built upon an SQLite database.[28]

Adoption[edit]

Web browsers[edit]

  • Mozilla Firefox and Mozilla Thunderbird store a variety of configuration data (bookmarks, cookies, contacts etc.) in internally managed SQLite databases, and even offer an add-on to manage SQLite databases.
  • Google's Chrome browser
  • The Opera Internet suite and browser uses SQLite 3.7.9 for managing WebSQL databases. This is noted in opera:about, although without the mention of WebSQL (databases can be managed through opera:webdatabases).
  • Embedding SQLite in web browsers has resulted in adding SQLite to the HTML5 Web Storage standard and after discussion inside the W3C Web Applications Working Group[29] the WebSimpleDB API proposal was developed.[30]

Web application frameworks[edit]

Various[edit]

Operating systems[edit]

Because of its small size, SQLite is well suited to embedded systems, and is also included in:

However, it is also suitable for desktop operating systems; Apple adopted it as an option in OS X's Core Data API from the original implementation in Mac OS X 10.4 onwards, and also for administration of videos and songs on the iPhone.

See also[edit]

Portal icon Free software portal
Portal icon Software portal
Portal icon IT portal

References[edit]

Notes[edit]

  1. ^ a b "SQLite Copyright". sqlite.org. Retrieved May 17, 2010. 
  2. ^ D. Richard Hipp (presenter) (May 31, 2006). An Introduction to SQLite (video). Google Inc. Event occurs at 00:01:14. Retrieved March 23, 2010. "[...] ess-kju-ellite [...]" 
  3. ^ D. Richard Hipp (presenter) (May 31, 2006). An Introduction to SQLite. Google Inc. Event occurs at 00:48:15. Retrieved March 23, 2010. "[...] sequelite [...]" 
  4. ^ "Distinctive Features Of SQLite". SQLite. June 14, 2012. Retrieved August 7, 2012. 
  5. ^ "Most Widely Deployed SQL Database Estimates". Sqlite.org. Retrieved May 11, 2011. 
  6. ^ "The source code for SQLite is in the public domain". Sqlite.org. Retrieved May 11, 2011. 
  7. ^ a b Owens, Michael (2006). The Definitive Guide to SQLite. Apress. doi:10.1007/978-1-4302-0172-4_1. ISBN 978-1-59059-673-9. 
  8. ^ "Interview: Richard Hipp on UnQL, a New Query Language for Document Databases". InfoQ. August 4, 2011. Retrieved October 5, 2011. 
  9. ^ MDB: A Memory-Mapped Database and Backend for OpenLDAP, Howard Chu, [MDB: A Memory-Mapped Database and Backend for OpenLDAP LDAPCon 2011].
  10. ^ sqlightning source code.
  11. ^ "SQL Features That SQLite Does Not Implement". SQLite. January 1, 2009. Retrieved October 14, 2009. 
  12. ^ "Frequently Asked Questions". SQLite. January 26, 2009. Retrieved February 7, 2009. 
  13. ^ "Write Ahead Logging in SQLite 3.7". SQLite. Retrieved September 3, 2011. "WAL provides more concurrency as readers do not block writers and a writer does not block readers. Reading and writing can proceed concurrently" 
  14. ^ "Web SQL Database". World Wide Web Consortium. December 22, 2009. Retrieved January 26, 2010. "all interested implementors have used the same SQL backend (Sqlite)" 
  15. ^ "Gears API". Database API. Google. Retrieved April 2, 2010. 
  16. ^ Coenraets, Christophe (January 19, 2010). "Using the SQLite database access API in Adobe AIR". Adobe. Retrieved April 2, 2010. 
  17. ^ "DOM Storage". Mozilla Developer Center. Retrieved February 9, 2010. 
  18. ^ "Case-insensitive matching of Unicode characters does not work". SQLite Frequently Asked Questions. Sqlite.org. Retrieved May 11, 2011. 
  19. ^ DBD::SQLite: Perl DBI Interface to SQLite
  20. ^ PySQLite: Python bindings for SQLite
  21. ^ SQLite/Ruby: Ruby bindings for SQLite
  22. ^ JSPDO JavaScript database access abstraction API
  23. ^ http://system.data.sqlite.org/index.html/doc/trunk/www/index.wiki
  24. ^ http://www.ch-werner.de/sqliteodbc/
  25. ^ http://documentation.openoffice.org/HOW_TO/data_source/SQLite.pdf
  26. ^ "sqlite — Sqlite Wrappers". SQLite. February 7, 2009. Retrieved February 7, 2009. 
  27. ^ "How SQLite Is Tested". SQLite. Retrieved September 12, 2009. 
  28. ^ "Fossil: Fossil Performance". Fossil-scm.org. August 23, 2009. Retrieved September 12, 2009. 
  29. ^ "Web Storage & SQL". W3C Web Applications Working Group mailing list. Retrieved February 10, 2011. 
  30. ^ "W3C WebSimpleDB API". W3C, www.w3.org. Retrieved February 10, 2011. 
  31. ^ "Databases". Django Documentation. Django Software Foundation. Retrieved 13 November 2012. 
  32. ^ "Drupal 7". 
  33. ^ "Skype client using SQLite?". Mail-archive.com. August 28, 2007. Retrieved June 14, 2010. 
  34. ^ "Well-Known Users of SQLite". Sqlite.org. Retrieved June 14, 2010. 
  35. ^ "Possible virus infection by Xmarks?". virusremoval.pro. June 23, 2010. Retrieved July 28, 2010. 
  36. ^ "Well-known Users of SQLite". Sqlite.org. Retrieved June 14, 2010. 

External links[edit]

Wikimedia Commons has media related to: SQLite
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