Add XML documentation.

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 68ff7afd039653c17b513341ccf574b0680018e4..c589c2c34556f16496341d6ead147ea3f52747a3 100644 (file)
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -1,4 +1,4 @@
-
+
 
  
   Data Types
@@ -3295,6 +3295,154 @@ SELECT * FROM pg_attribute
 
   
 
+  
+   <acronym>XML</> Document Support
+
+   
+    xml
+   
+
+   
+    XML (eXtensible Markup Language) support is not one
+    capability, but a variety of features supported by a database
+    system. These capabilities include storage, import/export,
+    validation, indexing, efficiency of modification, searching,
+    transforming, and XML to SQL mapping.
+    PostgreSQL supports some but not all of these
+    XML capabilities. Future releases of
+    PostgreSQL will continue to improve XML
+    support. For an overview of XML use in databases, see 
+    url="http://www.rpbourret.com/xml/XMLAndDatabases.htm">.
+   
+
+   
+
+   
+    Storage
+    
+
+     
+      PostgreSQL does not have a specialized XML data type.
+      Users should store XML documents in ordinary
+      TEXT fields. If you need the document split apart into
+      its component parts so each element is stored separately, you must
+      use a middle-ware solution to do that, but once done, the data
+      becomes relational and has to be processed accordingly.
+     
+    
+   
+
+   
+    Import/Export
+    
+
+     
+      There is no facility for mapping XML to relational
+      tables. An external tool must be used for this. One simple way to
+      export XML is to use psql in
+      HTML mode (\pset format html), and convert
+      the XHTML output to XML using an external tool.
+     
+    
+   
+
+   
+    Validation
+    
+
+     
+      /contrib/xml2 has a function called
+      xml_valid() that can be used in a CHECK
+      constraint to enforce that a field contains valid XML.
+      It does not support validation against a specific XML
+      schema. A server-side language with XML capabilities
+      could be used to do schema-specific XML checks.
+     
+    
+   
+
+   
+    Indexing
+    
+
+     
+      /contrib/xml2 functions can be used in expression
+      indexes to index specific XML fields. To index the
+      full contents of XML documents, the full-text indexing
+      tool /contrib/tsearch2 can be used. Of course,
+      tsearch2 indexes have no XML awareness so additional
+      /contrib/xml2 checks should be added to queries.
+     
+    
+   
+
+   
+    Modification
+    
+
+     
+      If an UPDATE does not modify an XML field,
+      the XML data is shared between the old and new rows.
+      However, if the UPDATE modifies an XML
+      field, a full modified copy of the XML field must be
+      created internally.
+     
+    
+   
+
+   
+    Searching
+    
+
+     
+      XPath searches are implemented using /contrib/xml2.
+      It processes XML text documents and returns results
+      based on the requested query.
+     
+    
+   
+
+   
+    Transforming
+    
+
+     
+      /contrib/xml2 supports XSLT (XML
+      Stylesheet Language Transformation).
+     
+    
+   
+
+   
+    XML to SQL Mapping
+    
+
+     
+      This involves converting XML data to and from
+      relational structures. PostgreSQL has no internal
+      support for such mapping, and relies on external tools to do such
+      conversions.
+     
+    
+   
+
+   
+    Missing Features
+    
+
+     
+   Missing features include XQuery, SQL/XML syntax (ISO/IEC
+   9075-14), and an XML data type optimized for
+   XML storage.
+   
+     
+    
+   
+
+   
+
+  
+