XML database: Difference between revisions

Revision as of 18:29, 29 May 2019

Revision as of 17:39, 30 May 2019

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* [[Metadata]] is often available as XML

* Semantic web data is available as [[Resource Description Framework|RDF]]/XML

* Provides a solution for [[Object-relational impedance mismatch]]<ref>[NoSQL Distilled: A Brief Guide to the Emerging World of Polyglot Persistence. Addison-Wesley Educational Publishers Inc, 2009] {{ISBN-13: |978-0321826626}}</ref>

Steve O'Connell gives one reason for the use of XML in databases: the increasingly common use of XML for [[transport layer|data transport]], which has meant that "data is extracted from databases and put into XML documents and vice-versa".<ref name=oconnell2005>{{cite report|author=O'Connell, Steve|work=Advanced Databases Course Notes|title="Section 9.2"|type=Syllabus|date=2005|publisher=[[University of Southampton]]|___location=Southampton, England}}</ref>{{update inline|date=March 2015}} It may prove more efficient (in terms of conversion costs) and easier to store the data in XML format. In content-based applications, the ability of the native XML database also minimizes the need for extraction or entry of metadata to support searching and navigation.

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#Microsoft SQL Server<ref name=sqlserver2005>{{cite web|title=Using XML in SQL Server|url=https://msdn.microsoft.com/en-us/library/ms190936.aspx|website=Microsoft Developer Network|publisher=[[Microsoft Corporation]]|accessdate=17 March 2015}}</ref>

#Oracle Database<ref name=oracle2>{{cite book|title=Oracle XML DB Developer's Guide, 10''g'' Release 2|date=August 2005|publisher=Oracle Corporation|chapter-url=http://docs.oracle.com/cd/B19306_01/appdev.102/b14259/xdb04cre.htm|accessdate=17 March 2015|chapter=XMLType Operations}}</ref>

#PostgreSQL<ref name=postgresql>{{cite book|title=PostgreSQL 9.6 Documentation|chapter-url=https://www.postgresql.org/docs/9.6/static/datatype-xml.html|accessdate=1 April 2017|chapter=8.13. XML Type}}</ref>

Typically an XML enabled database is best suited where the majority of data are non-XML. For datasets where the majority of data are XML, a [[#Native XML databases|native XML database]] is better suited.

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== Native XML databases ==

Native XML databases are especially tailored for working with XML data. As managing XML as large strings would be inefficient, and due to the hierarchical nature of XML, custom optimized data structures are used for storage and querying. This usually increases performance both in terms of read-only queries and updates.<ref>{{cite web|last1=Matthias|first1=Nicola|title=XML versus Relational Database Performance|url=https://nativexmldatabase.com/2010/08/22/xml-versus-relational-database-performance/|website=Native XML Database|accessdate=28 Jun 2017|date=22 August 2010}}</ref>. XML nodes and documents are the fundamental unit of (logical) storage, just as a [[relational database]] has fields and rows.

The standard for querying XML data per W3C recommendation is [[XQuery]]; the latest version is XQuery 3.1.<ref>{{cite web|url=http://www.w3.org/TR/xquery-31/ | title=XQuery 3.1 Recommendation | date=2017-03-21}}</ref> XQuery includes [[XPath]] as a sub-language and XML itself is a valid sub-syntax of XQuery. In contrast to XML enabled databases, native databases provide full support for XQuery. In addition to XPath, some XML databases support [[XSLT]] as a method of transforming documents or query results retrieved from the database.