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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

<?end ?>
Peter Eisentraut XML Support