SQL/XML for Developers

Lewis CunninghamSenior Solutions ArchitectEnterpriseDBLewis.cunningham@enterprisedb.co

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Postgres Rocks!

Agenda

What is XML?

What is the XML data type?

What is SQL/XML?

What should(n’t) I do with XML?

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What is XML?

<?XML?>

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What is XML?

Semi-Structured Hierarchical Not relational Not freeform

Markup “Language” Tags Identify Data <NAME>Lewis</NAME>

Human AND machine readable

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What is XML?

Elements Root Element Child Elements

Elements are nodes Some nodes contain elements Some nodes contain character data A node can contain both

Namespaces

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What is XML?

Well Formed XML Follows XML formatting rules

All open tags have closing tags All attribute values are enclosed in quotes

If a document is not well formed, it is not XML A well formed document may not be a VALID document

Valid XML Conforms to a specific specification (DTD, XSD, RNG) A valid document will always be a well formed

document

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What is XML?

Simple Example

<rootnode><childnode1>Some Data</childnode1><childnode2>Some more

<additional>data</additional></childnode2><emptytag />

</rootnode>

Element/Tag

ClosingTag

Childnode1Child to rootnode

EmptyTag

Childnode1 isSibling tochildnode2

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What is XML?

Namespaces

A namespace prevents naming collisions

A namespace provides clarity

A namespace allows multiple documents to be combined into a single document

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What is XML?

Simple Example

<rootnode xmlns:abc='http://abc.org/xml' ><abc:xml:childnode1>Some Data</abc:childnode1><abc:childnode2>Some more

<additional>data</additional> </abc:childnode2>

<emptytag /></rootnode>

NamespaceIdentifier

NamespaceUsage

NamespaceName

NamespaceURI

Default Usage

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What is XML?

Describing XML

DTD – Document Type Description

XSD – XML Schema

Relax NG – REgular LAnguage for Xml Next Generation

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What is XML?

DTD

A list of valid elements and attributesMay be inline or externalOriginal descriptive languageLimited and mostly obsoleteNo data type definitionsNo support for Namespaces

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DTD Example

<!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]>

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What is XML?

XSD

The XML Schema is the W3C replacement to DTDs

XSD supports data types an namespacesXML Schemas are defined as XMLAllows you to define ordering/number of

elementsAllows you to define mandatory elementsXML Schemas are extensible

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XSD Example

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="product" type="ProductType"/> <xsd:complexType name="ProductType"> <xsd:sequence> <xsd:element name="number" type="xsd:integer"/> <xsd:element name="size" type="SizeType"/> </xsd:sequence> <xsd:attribute name="effDate" type="xsd:date"/>

</xsd:complexType> <xsd:simpleType name="SizeType"> <xsd:restriction base="xsd:integer"> <xsd:minInclusive

value="2"/> <xsd:maxInclusive value="18"/> </xsd:restriction>

</xsd:simpleType> </xsd:schema>

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What is XML?

RELAX NG

XML and non-XML formatsSimpler than XSDMore like a speaking dialect than an XML

dialectSupports data types and namespacesNot as robust as XSD (fewer data types, not as

many rules (defaults and such)Not as widely utilized as XSD

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RELAX NG (XML) Example

<element name="patron" xmnln="http://relaxng.org/ns/structure/1.0"> <interleave> <element name="name"><text/></element> <element name="id-num"><text/></element> <zeroOrMore> <element name="book"> <choice> <attribute name="isbn"/> <attribute name="title"/> </choice> </element> </zeroOrMore> </interleave> </element>

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RELAX NG (Compact) Example

element patron { element name { text } & element id-num { text } & element book { (attribute isbn { text } | attribute title { text } ) }* }

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What is the XML data type?

Postgres 8.3 Data Type

Text based

Well formed check

Non-validating

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What is the XML data type?

XML Document <onlyoneroot>

data goes here</onlyoneroot>

XML Content (fragment)<name>Lewis</name><sex>yes</sex>

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What is the XML data type?

Declare a column as XMLcreate table xml_tab (

id integer,data XML );

Declare a variable as XMLDECLARE v_xml XML;BEGIN……

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What is SQL/XML?

SQL/XML

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What is SQL/XML?

SQL/XML (or SQL/X) is standards based

Combines XML and SQL

IBM, Oracle, Microsoft and Sybase all played a large part in defining SQL/XML

Home on the web: www.sqlx.org

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What is SQL/XML?

SQL/XML defines a set of mappings and a set of functions

Based on XQuery and XPath

Postgres 8.3 implements the core functions of SQL/XML

XQuery is not yet supported in Postgres

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What is SQL/XML?

SQL/X Functions XMLParse XMLSerialize XMLElement XMLForest XMLAgg XMLAttributes XML Comment XMLConcat Xpath

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What is SQL/XML?

Sample data

CREATE TABLE EMP( LAST_NAME text, EMP_ID integer NOT NULL, FIRST_NAME text, DEPT_ID integer, SALARY integer, CONSTRAINT EMP_pkey PRIMARY KEY (EMP_ID))WITH (OIDS=FALSE);

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What is SQL/XML?

Sample tableINSERT INTO EMP(

LAST_NAME, EMP_ID, FIRST_NAME, DEPT_ID, SALARY)VALUES ('Blow', 1, 'Joe', 1, 10000), ('Head', 2, 'Helmut', 1, 12000), ('Jack', 3, 'Noe', 1, 12000), ('Hard', 4, 'Blow', 2, 20000), ('First', 5, 'Hugo', 2, 21000), ('Spaem',6, 'Kingoof', 2, 20000), ('Ventura', 7, 'Ace', 3, 35000), ('Nickleby', 8, 'Nick', 3, 400000), ('Budd', 9, 'Billy', 4, 99000), ('Cleaver', 10, 'Wally', 4, 100000) ;

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What is SQL/XML? - XML Parse

XMLParse turns text into XML

vXMLVar := XMLParse(CONTENT ‘<root>data</root>’);

vXMLVar := XMLParse(DOCUMENT ‘<root>data</root>’);

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What is SQL/XML? - XMLSerialize

XMLSerialize turns XML into text

vString := XMLSerialize( DOCUMENT v_xml AS TEXT);

vString := XMLSerialize( CONTENT v_xml AS TEXT);

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What is SQL/XML? - XMLElement

SELECT XMLElement(name main, last_name) from emp;

<main>Blow</main>

<main>Head</main>

<main>Jack</main>

<main>Hard</main>

<main>First</main>

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What is SQL/XML? – XMLElement Cont’d

SELECT XMLElement(name main, last_name), XMLElement(name main, first_name)FROM emp;

<main>Blow</main> | <main>Joe</main>

<main>Head</main> | <main>Helmut</main>

<main>Jack</main> | <main>Noe</main>

<main>Hard</main> | <main>Blow</main>

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What is SQL/XML? - XMLForest

SELECT XMLForest(last_name, first_name)FROM emp;

<last_name>Blow</last_name><first_name>Joe</first_name>

<last_name>Head</last_name><first_name>Helmut</first_name>

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What is SQL/XML? – XMLForest Cont’d

SELECT XMLElement(name main, XMLForest(last_name, first_name) )FROM emp;<main>

<last_name>Blow</last_name>

<first_name>Joe</first_name>

</main>

<main>

<last_name>Head</last_name>

<first_name>Helmut</first_name>

</main>

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What is SQL/XML? – XMLAgg

SELECT XMLAgg( XMLForest(last_name, first_name) )FROM emp; <last_name>Blow</last_name>

<first_name>Joe</first_name>

<last_name>Head</last_name>

<first_name>Helmut</first_name>

<last_name>Jack</last_name>

<first_name>Noe</first_name>…

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What is SQL/XML? – XMLAgg Cont'd

SELECT XMLElement(name main, XMLAgg(XMLForest(last_name, first_name) ))FROM emp;<main>

<last_name>Blow</last_name>

<first_name>Joe</first_name>

<last_name>Head</last_name>

<first_name>Helmut</first_name>

<last_name>Jack</last_name>

<first_name>Noe</first_name>…

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What is SQL/XML? - XMLAttributes

SELECT XMLElement(name main, XMLAttributes(nextval('t_seq') AS rownum) )

FROM emp;

<main rownum="1"/>

<main rownum="2"/>

<main rownum="3"/>

<main rownum="4"/>

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What is SQL/XML? – XMLAttributes Cont’d

CREATE TEMP SEQUENCE t_seq;

SELECT XMLElement(name main, XMLAttributes(nextval('t_seq') AS rownum),

XMLForest(last_name, first_name) )FROM emp;

DROP SEQUENCE t_seq;

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What is SQL/XML? – XMLAttributes Cont’d

<main rownum="1"> <last_name>Blow</last_name>

<first_name>Joe</first_name>

</main>

<main rownum="2">

<last_name>Head</last_name>

<first_name>Helmut</first_name>

</main>

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What is SQL/XML? – Concatenating Columns

SELECT XMLElement(name main, XMLForest(last_name || ',' || first_name AS fullname, salary) ) FROM emp; <main> <fullname>Blow,Joe</fullname>

<salary>10000</salary>

</main>

<main>

<fullname>Head,Helmut</fullname>

<salary>12000</salary>

</main>

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What is SQL/XML? – Concat and Attributes

SELECT XMLElement(name main, XMLElement(name fullname, XMLAttributes(dept_id), last_name || ',' || first_name

), XMLForest(salary) ) FROM emp;

<main>

<fullname dept_id="1">

Blow,Joe</fullname>

<salary>10000</salary>

</main>

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What is SQL/XML? - XMLComment

SELECT XMLElement(name main, XMLComment('Comment goes here'),

XMLForest(last_name, first_name))FROM emp;<main>

<!—Comment goes here-->

<last_name>Blow</last_name>

<first_name>Joe</first_name>

</main>

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What is SQL/XML? - XMLConcat

SELECT XMLElement(name lastname, last_name), XMLElement(name firstname, first_name)FROM emp;

<lastname>Blow</lastname> | <firstname>Joe</firstname>

<lastname>Head</lastname> | <firstname>Helmut</firstname>

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What is SQL/XML? – XMLConcat Cont'd

SELECT XMLConcat( XMLElement(name lastname, last_name), XMLElement(name firstname, first_name) )FROM emp;

<lastname>Blow</lastname><firstname>Joe</firstname>

<lastname>Head</lastname><firstname>Helmut</firstname>

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What is SQL/XML? – XMLConcat Cont'd

SELECT XMLElement(name main, XMLConcat( XMLElement(name lastname, last_name), XMLElement(name firstname, first_name) ) )FROM emp;<main>

<lastname>Blow</lastname>

<firstname>Joe</firstname>

</main>

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What is SQL/XML? – XML Tables

CREATE TABLE xmltab (col1 XML);

INSERT INTO xmltab ( SELECT XMLElement(name main,

XMLConcat( XMLElement(name lastname, last_name), XMLElement(name firstname, first_name) )

) FROM emp);

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What is SQL/XML? – XML Table

SELECT * FROM xmltab;

<main><lastname>Blow</lastname><firstname>Joe</firstname></main>

<main><lastname>Head</lastname><firstname>Helmut</firstname></main>

<main><lastname>Jack</lastname><firstname>Noe</firstname></main>

<main><lastname>Hard</lastname><firstname>Blow</firstname></main>

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What is SQL/XML? - XPath

XPath is a language for navigating through nodes in an XML document

XPath is hierarchicalThink of XPath like navigating directories in a

file systemAn XPath expression may point to

A Node (like a directory) Data (like a file) Functions (like file properties or file values)

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What is SQL/XML? – Xpath Cont'd

SELECT Xpath('/main/firstname/text()', col1) FROM xmltab;

xpath

-----------

{Joe}

{Helmut}

{Noe}

{Blow}

{Hugo}

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What is SQL/XML? – Xpath Cont'd

SELECT textcol[1] FROM ( SELECT xpath('/main/firstname/text()', col1) AS

textcol FROM xmltab ) AS xmlsource;

textcol

---------

Joe

Helmut

Noe

Blow

Hugo

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What is SQL/XML? – XML from a Query

select query_to_xml('select * from emp', TRUE, TRUE, '');

<row xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<last_name>Blow</last_name>

<emp_id>1</emp_id>

<first_name>Joe</first_name>

<dept_id>1</dept_id>

<salary>10000</salary>

</row>

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What is SQL/XML? – XML from a Table

select table_to_xml('emp', TRUE, TRUE, '');

<emp xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<last_name>Blow</last_name>

<emp_id>1</emp_id>

<first_name>Joe</first_name>

<dept_id>1</dept_id>

<salary>10000</salary>

</emp>

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What should(n’t) I do with XML?

XML

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What should(n’t) I do with XML?

PostgreSQL is a RELATIONAL database

Store your data relationally, unless Your XML is read only Your XML is transient Your XML is fairly static Your XML is very small You have a discrete key external to the XML Preserved white space is critical

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What should(n’t) I do with XML? Cont'd

Convert your XML to Relations by Shredding Map your relational schema to the XML by its Schema

or DTD Use XPath to extract columnar data

Use SQL/XML to recreate the original XML document

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What should(n’t) I do with XML? Cont'd

Relational data is much easier to Index Update Manipulate

XML data is better for Use by some programming languages CMS systems Very unstructured data For reporting

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What should(n’t) I do with XML? Cont'd

XML is great for Public stored procedure interfaces

Publish the XML spec Include a version element or attribute Change parameters and let users adapt over time

Web based processing Many web apps support XML XML + XSLT = Web Happiness

Data interfaces Platform independent Current parsers are fast Validation and versioning built-in Public Specifications

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SQL/XML for Developers

Lewis CunninghamSenior Solutions ArchitectEnterpriseDBLewis.cunningham@enterprisedb.co

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