Download XML Databases – do they really exist? - Indico

ELAG 2005 at CERN, Geneva
XML Databases – do they really
exist?
Jan Erik Kofoed
BIBSYS Library Automation
Design goals for XML
1.
2.
3.
4.
XML shall be straightforwardly usable over the Internet.
XML shall support a wide variety of applications.
XML shall be compatible with SGML.
It shall be easy to write programs which process XML
documents.
5. The number of optional features in XML is to be kept to the
absolute minimum, ideally zero.
6. XML documents should be human-legible and reasonably clear.
7. The XML design should be prepared quickly.
8. The design of XML shall be formal and concise.
9. XML documents shall be easy to create.
10. Terseness in XML markup is of minimal importance.
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A simple example
<?xml version="1.0" encoding="UTF-8"?>
<book id="231456">
<author>Henrik Ibsen</author>
<title>The Wild Duck</title>
<published>
<place>London</place>
<year>1890</year>
</published>
</book>
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A relational model for the example
book
published
id (primary key
publ-id (foreign key)
author
publ-id (primary key)
place
year
title
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Realisation as tables
book
id
publ-id
author
title
231456
0001
Henrik
Ibsen
The Wild
Duck
published
publ-id
place
year
0001
London
1890
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Realisation as DOM Document Object Model
book
id
231456
autho
r
Henrik Ibsen
title
The Wild Duck
published
element node
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attribute node
6
place
London
year
1890
text node
ELAG 2005
Important W3C XML technologies
• XML Schema
– defining database schema, instance validation
• XPath
– query expressions
– addressing content
• XQuery
– a new query language for XML
– based on XPath and XML Schema type hierarchy
• Namespaces in XML
– qualification of content
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XML Schema – text representation
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="book">
<xs:complexType>
<xs:sequence>
<xs:element name="author" type="xs:string"/>
<xs:element name="title" type="xs:string"/>
<xs:element name="published">
<xs:complexType>
<xs:sequence>
<xs:element name="place" type="xs:string"/>
<xs:element name="year" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="id" use="required" type="xs:int"/>
</xs:complexType>
</xs:element>
</xs:schema>
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XML Schema – graphical
representation
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Assigning schema to a XML
document
<?xml version="1.0" encoding="UTF-8"?>
<book id="231456"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="book.xsd">
<author>Henrik Ibsen</author>
<title>The Wild Duck</title>
<published>
<place>London</place>
<year>1890</year>
</published>
</book>
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XQuery
The query:
for
$query in doc("book.xml")
where $query/book/author = "Henrik Ibsen"
return
<result>
{$query/book/title}
XPath
</result>
gives this result:
<result>
<title>The Wild Duck</title>
</result>
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Native XML database
1. Defines a (logical) model for an XML
document -- as opposed to the data in that
document -- and stores and retrieves
documents according to that model.
2. Has an XML document as its fundamental
unit of (logical) storage.
3. Is not required to have any particular
underlying physical storage model.
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SAG Tamino XML Server
1. Database Schema based on W3C XML
Schema.
2. The basic record-type is a well-formed XML
document type.
Different document types can be grouped into
collections.
3. Stores data as serialised DOM objects.
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Tamino System Architecture
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ORACLE XML Database
•
•
•
•
Includes a native XML datatype
SQL operators on XML content
Support for W3C XML Schema
XML/SQL duality
– XML operations on relational data
– SQL operations on XML data
• Support for XPath and SQL/XML
• XML mapped to file/folder structure
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ORACLE – storage options
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ORACLE – Create statement
CREATE TABLE purchase_order_table
(
po_number NUMBER(16),
purchase_order XMLTYPE
)
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ORACLE – Insert statement
INSERT INTO purchase_order_table
VALUES (1234, XMLTYPE(
'<PurchaseOrder>
<Reference>BLAKE-2002-015</Reference>
<Actions/>
<Reject/>
<Requestor>David E. Blake</Requestor>
<User>BLAKE</User>
<CostCenter>S30</CostCenter>
</PurchaseOrder>‘
)
)
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ORACLE – Select statement
Database content:
<PurchaseOrder>
<Reference>BLAKE-2002-015</Reference>
<Actions/>
<Reject/>
<Requestor>David E. Blake</Requestor>
<User>BLAKE</User>
<CostCenter>S30</CostCenter>
</PurchaseOrder>
XPath
SQL query:
SELECT extractValue(p.purchase_order,'/PurchaseOrder/User')
FROM purchase_order_table p
WHERE existsNode(p.purchase_order,'/PurchaseOrder[CostCenter="S30"]') = 1
Result:
EXTRACTVALUE(P.PURCHASEORDER,’/PURCHASEORDER/USER’)
----------------------------------------------------------------------------------------------------------BLAKE
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SQL 2003 and SQL/XML
• New ANSI/ISO SQL standard:
Information technology — Database
languages — SQL — Part 14: XML-Related
Specifications (SQL/XML). Final comittee draft
– new XML type
– mapping between SQL- and XML-constructs
– functions for generating XML from SQL data.
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XML database implementations
Ronald Bourret: XML Database Products
• Native XML databases
– 24 commercial
– 14 open source
• XML enabled databases
– mostly RDBMS
– 16 commercial
• XML Servers
– mostly based on RDBMS
– 19 commercial
– 5 open source
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XML Databases at BIBSYS
• Software: Tamino XML Server from Software AG
–
–
–
–
–
–
Native XML database
Supports XML Schema, Namespaces, XPath, and XQuery
Stores both XML and binary objects (images, video a.o.)
Communication based on HTTP
Uses Apache web server as frontend
Java API used for programming
• BIBSYS Galleri
– a database of images
• BIBSYS Subject Portal
– a metadata database for high quality web resources
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BIBSYS Galleri
•
•
•
•
a database of images
metadata in MARC wrapped in XML
images stored in JPEG format (nonXML data)
Database schema generated from DTD (Document
Type Definition)
• XPath used as query language
• XML content transfomed using XSLT into HTML for
presentation
• URL: http://bilde.bibsys.no
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BIBSYS Galleri – xml format (extract)
<?xml version="1.0" encoding="iso-8859-1" ?>
<marc id="UBT-TO-004680A" type="BILDEMARC" utgave="1.0">
<f012>
<f012e>2002-04-27</f012e>
<f012k>IJGR</f012k>
</f012>
<f096>
<f096a>UBiT</f096a>
<f096b>topografisk</f096b>
<f096c>VII-Uhj md-004680A</f096c>
<f096f>Prospektkort s/h</f096f>
</f096>
<f100>
<f100a>Hovde, L.E.</f100a>
<f100c>forlag</f100c>
</f100>
<f245>
<f245a>Olav Tryggvasons gate fra Bakke bro med trikk og hest.</f245a>
</f245>
</marc>
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BIBSYS Subject Portal
•
•
•
•
Metadata for high quality web resources
Uses a subject hierarchy based on Dewey
Data in XML using several namespaces
Database schema written as several XML
Schemas, one for each namespace
• XQuery (working draft from 2002-08-16) used as query
language
• URL: http://emneportal.bibsys.no
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BIBSYS Subject portal – xml format
(extract)
<ep:eprecord xmlns:ep="http://www.bibsys.no/eprecord/"
xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcterms="http://purl.org/dc/terms/"
xmlns:epres="http://www.bibsys.no/res_type/" xmlns:epadm="http://www.bibsys.no/epadm/"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" recid="983870854-8343">
<ep:head>
<epadm:identifier>983870854-8343</epadm:identifier>
<epadm:status>godkjent</epadm:status>
</ep:head>
<ep:biblio>
<dc:title>Cognitive Psychology Online Laboratory : CogLab</dc:title>
<dc:type xsi:type="epres:resource">BM</dc:type>
<ep:uriandaccess>
<dc:identifier xsi:type="dcterms:URI">http://coglab.wadsworth.com/</dc:identifier>
<dcterms:accessRights>FREEE</dcterms:accessRights>
</ep:uriandaccess>
</ep:biblio>
<ep:admin>
<epadm:created>2001-03-06</epadm:created>
</ep:admin>
</ep:eprecord>
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Conclusion
• Two main kind of XML Databases
– native
– RDBMS with extention
• XML databases well suited for storing
hierarchial structures
• Work in progress to join SQL and XML based
functionality
• DBMS will in future handle relational data and
xml base data equally well
• Yes, XML databases, - indeed exist!
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