XML Technology

Emerging Importance of XML

– HTML-tagging is display oriented.– XML-based content tagging has important uses:

• data mining• role-oriented display customization• intelligent searching and other value

added elements– Wide spread industry support for this new open

standard• Microsoft• Netscape• W3C is pushing the standardization

efforts– Complementary technology to HTML-based web

browsers

Requirements best addressed by XML

• Customizing front-end applications - easy presentation of what users want to see

• Data mining - ala altavista-type search• Synthesis type applications - combining

multiple information sources• Electronic commerce-type applications

XML Markup

• Elements and attributes• Entity References• Comments• Processing Instructions• Marked Sections• Document Type Definitions (DTDs)

Elements

• Bounded by start and end tags• Sample markup

<Patient> <FirstName> Frank</FirstName> <LastName> Foster</LastName>

</Patient>

• Patient, LastName, FirstName are all entity tags.

Attributes

• Name-value pairs included as part of start tags.

• Sample markup<APatient patientID=“123” FirstName=“Frank”

LastName=“Foster”><Insurance> Blue Cross </Insurance><Insurance> HMO </Insurance>

</APatient>

• FirstName and LastName in the example above are attribute declarations.

XML Aspects

• Entity References– used to represent special characters– to include content of external files– to represent blocks of repeated text– to insert unicode characters– to use an entity such as &amp e.g. “O’Reilly

&amp; Associates, Inc.”

• Comments<!-- this is how a comment starts and ends --

>

XML Aspects Continued

• Processing Instructions<?name pidata?>where ?name is an application that needs to

run and pidata? is parameters that needs to be passed to the application.

• CDATA sections– like <PRE> tag in HTML

<![CDATA[unprocessed text goes here…..

]]>

Document Type Definitions

• Allows the expression of constraints on tags• Defines sequencing and nesting of tags• Defines attributes and values and defaults• Allows specification of external file references• Four kinds of declarations in XML

– Element declarations– Attribute List declarations– Entity declarations– notation declarations

DTD Element Declarations

<!Element Patient (FirstName, LastName, Insurance?)>

Says that Patient info is composed of FirstName, LastName and optionally Insurance information.

<!Element Insurance (#PCDATA)>

Says element Insurance is composed of parse-able character data.

DTD Attribute List Declaration

<!ATTLIST Apatient patientID ID #requiredFirstName CDATALastName CDATA >

Other aspects of DTD

• Entity declarations (sort of macro capabilities)

• DTDs can be included with the tagged document or referred to externally.

• Distinction between “well-formed” and “valid” documents

• Well-formed: satisfy XML markue constraints - no associated DTD.

• Valid documents: XML markup that adhere to the constraints specified in a DTD.

XML’s evolving family of standards

• XML Linking Specification (XLL)• Resource Directory Framework (RDF)• Style sheets

– DSSSL - Document Style Semantics and Specification Language

– CSS Cascading Style sheets– XSL XML Style Specification Language

• Document Object Model• Document Content Descriptors and

Schemas