This document summarizes Peter Eisentraut's presentation on XML support in PostgreSQL. It discusses the types of XML support including an XML data type, XML export format, and mapping XML documents to SQL databases. It also outlines specifications like SQL/XML, features of the XML data type, functions for input, output, and querying XML, and the status and future of XML support in PostgreSQL.

1. XML Support
Specifications and Development
Peter Eisentraut
PostgreSQL Anniversary Summit
July 8–9, 2006
Toronto
Peter Eisentraut XML Support

2. XML Support
Types of “XML Support”:
XML data type and support functions
XML export format
Mapping XML documents to SQL databases
Peter Eisentraut XML Support

3. Specifications
ISO/IEC 9075-14:2003 (“XML-Related Specifications” –
SQL/XML)
ISO/IEC 9075-14:2006, as of 2006-06-12
Already implemented by IBM DB/2, Microsoft SQL Server,
OpenLink Virtuoso, Oracle, . . .
More information: http://www.sqlx.org/
Peter Eisentraut XML Support

4. XML Data Type
CREATE TABLE test (
...,
data xml,
...
);
Features:
Input checking
Support functions
Peter Eisentraut XML Support

5. XML Input/Output
No string literals as input
XMLPARSE ( DOCUMENT|CONTENT value ) --> xml
XMLSERIALIZE ( DOCUMENT|CONTENT xmlvalue AS
varchar ) --> varchar
These could serve as PostgreSQL input/output functions.
Peter Eisentraut XML Support

6. XML Support Functions
XMLCOMMENT
XMLCONCAT
XMLELEMENT
XMLFOREST
XMLPI
XMLROOT
XMLAGG
IS DOCUMENT, IS NOT DOCUMENT
Peter Eisentraut XML Support

7. XMLELEMENT Example
XMLROOT ( <?xml version=’1.0’
XMLELEMENT ( standalone=’yes’ ?>
NAME ’gazonk’, <gazonk name=’val’
XMLATTRIBUTES ( num=’2’>
’val’ AS ’name’, <qux>foo</qux>
1 + 1 AS ’num’ </gazonk>
),
XMLELEMENT (
NAME ’qux’,
’foo’
)
),
VERSION ’1.0’,
STANDALONE YES
)
Peter Eisentraut XML Support

8. XMLFOREST Example
SELECT xmlforest (
"FirstName" as "FName", "LastName" as "LName",
’string’ as "str", "Title", "Region" )
FROM "Demo"."demo"."Employees";
might result in
<FName>Nancy</FName>
<LName>Davolio</LName>
<str>string</str>
<Title>Sales Representative</Title>
<Region>WA</Region>
. . .
<FName>Anne</FName>
<LName>Dodsworth</LName>
<str>string</str>
<Title>Sales Representative</Title>
(1 row per record)
Peter Eisentraut XML Support

9. XMLAGG Example
SELECT xmlelement (’Emp’,
xmlattributes (’Sales Representative’ as "Title"),
xmlagg (xmlelement (’Name’, "FirstName", ’ ’,
"LastName")))
FROM "Demo"."demo"."Employees"
WHERE "Title" = ’Sales Representative’;
might result in
<Emp Title="Sales Representative">
<Name>Nancy Davolio</Name>
<Name>Janet Leverling</Name>
<Name>Margaret Peacock</Name>
<Name>Michael Suyama</Name>
<Name>Robert King</Name>
<Name>Anne Dodsworth</Name>
</Emp>
(1 row)
Peter Eisentraut XML Support

10. SQL:2006
More specific XML data type:
XML
XML(DOCUMENT)
XML(CONTENT)
XML(SEQUENCE)
XML(DOCUMENT(ANY))
XML(DOCUMENT(UNTYPED))
XML(DOCUMENT(XMLSCHEMA ’http://...’))
More functions:
XMLDOCUMENT
XMLTEXT
XMLVALIDATE
IS CONTENT
IS VALID
More options everywhere
XQuery
Peter Eisentraut XML Support

11. XML Data Type Status
Current status:
Google Summer of Code project works on SQL:2003
(Nikolay Samokhvalov)
Previous patches for support functions available, but work
with text data type (Pavel Stehule)
Also:
Integrate contrib/xml functionality
Peter Eisentraut XML Support

12. Implementation Issues
Uses libxml (LGPL)
Encoding handling
Memory management
Optional/mandatory?
Peter Eisentraut XML Support

13. For the Future
XQuery support (SQL:2006)
Ctree indexes
Peter Eisentraut XML Support

14. XML Export Format
Map SQL schema to XML Schema
Map database contents to XML document
Useful for:
Postprocessing using XSLT
pg_dump
psql?
Peter Eisentraut XML Support

15. Mapping Names
SQL <identifier> fully-escaped XML name partially-escaped XML name
employee EMPLOYEE EMPLOYEE
"employee" employee employee
"hire date" hire_x0020_date hire_x0020_date
"comp_plan" comp_x005F_plan comp_x005F_plan
"dept:id" dept_x003A_id dept:id
xmlcol _xFFFF_xmlcol xmlcol
Peter Eisentraut XML Support

16. XML Schema Mapping Example
CREATE TABLE test (a int PRIMARY KEY, b varchar(200));
is mapped to
<xsd:complexType name="RowType.catalog.schema.test">
<xsd:sequence>
<xsd:element name="a" type="INTEGER"></xsd:element>
<xsd:element name="b" type="VARCHAR_200_200"
minOccurs="0"></xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="TableType.catalog.schema.test">
<xsd:sequence>
<xsd:element name="row"
type="RowType.catalog.schema.test"
minOccurs="0"
maxOccurs="unbounded" />
</xsd:sequence>
</xsd:complexType>
Peter Eisentraut XML Support

17. XML Export Format Example
<catalogname>
<schemaname>
<tablename>
<row>
<colname1>value</colname1>
<colname2 xsi:nil=’true’/>
...
</row>
...
</tablename>
...
</schemaname>
...
</catalogname>
Peter Eisentraut XML Support

18. XML Export Format Status
Prototype available
Would like XML data type first
Where to put it?
pg_dump?
psql?
user-defined functions?
Peter Eisentraut XML Support

19. <?end ?>
Peter Eisentraut XML Support