Database - Discussions

XML: Extensible Markup Language

Dr. Buleje

Introduction

 Databases function as data sources for Web

applications

 HTML

 Used in static Web pages

 XML, JSON

 Self-describing documents

 Dynamic Web pages

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Structured, Semistructured, and

Unstructured Data

 Structured data

 Semi-structured data

 Un-structured data

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Directed Graph Model for

Semistructured Data

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Figure: Representing semistructured data as a graph

Structured, Semistructured, and

Unstructured Data (cont’d.)

 HTML uses predefined tags

 Document header

 Body

 Table tags

 Attributes

 Large number of predefined tags

 XHTML

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XML Hierarchical (Tree) Data Model

 Basic object: XML document

 Element

 Attribute

 Document types

 Data-centric

 Document-centric

 Hybrid

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XML Documents, and XML Schema

 Conditions for well-formed XML documents

 Notation for specifying elements

 elementname* indicates optional multivalued (repeating) element

 elementname+ indicates required multivalued (repeating) element

 elementname? indicates optional single-valued (non-repeating) element

 elementname indicates required single-valued (non-repeating) element

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XML Documents, and XML Schema

(cont’d.)

 Notation for specifying elements (cont’d.)

 Type specified by parentheses following the

element name

 !ATTLIST used to specify attributes within the element

 Parentheses can be nested when specifying elements

 Bar symbol (e1|e2) indicates either e1 or e2 can appear in the document

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XML Schema

 XML schema language

 XML namespace

 Elements and types

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XML Schema (cont’d.)

 Keys

 Complex elements

 xsd:complexType

 Composite attributes

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Storing and Extracting XML

Documents from Databases

 File system / DBMS: store documents as text

 DBMS to store document contents as data

elements

 Design specialized system to store XML data

 Create or publish custom XML documents from

preexisting relational databases

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XML Languages

 Query language standards

 XPath

 XQuery

 Specifying XPath expressions in XML

 Example

 For COMPANY.XML document stored at location

www.company.com/info.XML

 doc(www.company.com/infor.XML)/company

returns company root node and all descendant

nodes

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XQuery: Specifying Queries in XML

 FLWOR expression

 Variables preceded with $

 FOR assigns variable to a range

 WHERE specifies additional conditions

 ORDER BY specifies order of result elements

 RETURN specifies elements for retrieval

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XQuery: Specifying Queries in XML

 Example

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XML/SQL: SQL Functions for

Creating XML Data

 XMLELEMENT

 XMLFOREST

 XMLAGG

 XMLROOT

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XML/SQL: SQL Functions for

Creating XML Data (cont’d.)

 XMLATTRIBUTES

 Creates attributes for the elements of the XML

result

 Example: create XML element containing the

EMPLOYEE lastname for the employee with SSN

123456789

 Result:

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Summary

 Structured, semistructured, and unstructured data

 Hierarchical data model of XML standard

 Languages for specifying structure

 Approaches for storing XML documents

 XPath and XQuery languages

 SQL/XML allows formatting query results as XML

data

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