xml: the promise and the reality



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XML will

replace

HTML XML is for XML is for documentsdocuments

XML is f

or

XML is f

or

datadata

XML will XML will replace all replace all message message formatsformats

And clear the standards And clear the standards log jam!log jam!



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Profile Edit ScreenNAME: K. Scott Morrison

ADDRESS: 8999 Nelson Way

CITY: Burnaby STATE/PROV: B.C.

COUNTRY: Canada CODE: V5A 4B5

TEL: (604) 293-5753 FAX: (604) 473-5807

CREDIT CARD1

TYPE: VISA NUM: 123456789 EXP: 12/00

CREDIT CARD2

TYPE: AMEX NUM: 987654321 EXP: 04/01



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Screen ScrapeScreen Scrape

Scr

een

Scr

ape

Persistent Store

Ser

ver

Remote System

…….. .. … … … ..



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Binary RepresentationBinary Representation



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Binary RepresentationBinary Representation• Issues

– Can’t determine structure from data– Portability– Fixed field length

• Brittle interfaces– Must modify all clients and servers simultaneously

• Mapping code typically buried in applications– Significant maintenance problem

• Distribution of message map– Not human readable



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ANSI_X3.4-1968 (US-ASCII) ANSI_X3.4-1968 (US-ASCII) Text RepresentationText Representation



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US-ASCII Text RepresentationUS-ASCII Text Representation• Standards-based, reasonably portable• Human readable• Can make conjectures about semantics• Issues:

– Limited character set• NLS problems

– No real structure: hierarchy, lists, etc– Still very brittle– Distribution of message maps



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Proprietary TaggingProprietary Tagging

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Proprietary TaggingProprietary Tagging• Human understandable• Less brittle interface

– Delimited text using tag and <CR> • Issues

– Distribution of tag semantics– Non-standard– Character escaping issues

• E.g. <CR>, :, etc– No sense of hierarchy– Programmer intensive: parsers, handlers, etc



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Formalized Tagging: MarkupFormalized Tagging: Markup• Markup is meta-data

– Adds information about text– What it means, how to interpret, how to render, etc

• Markup delimits– START-----------END– Interface is less brittle

• Markup works as a container• Markup adds structure

– Hierarchy, etc

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Markup Can Be StylisticMarkup Can Be Stylistic



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Markup Can Be StructuralMarkup Can Be Structural

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 Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. 

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Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat.

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Markup Can Be SemanticMarkup Can Be Semantic

<TITLE>Lorem ipsum dolor sit amet.</TITLE>

<BODY>consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. </BODY>

Lorem ipsum dolor sit amet.

consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat.

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Simple Markup Example #1Simple Markup Example #1

<Message>Hello, World!

</Message>

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Simple Markup Example #2Simple Markup Example #2<MessageContainer>

<Message> Hello, World! </Message>

<Message> Goodbye, World! </Message>

</MessageContainer>

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Profile Using MarkupProfile Using Markup<Profile> <Name> K. Scott Morrison </Name> <Address> 8999 Nelson Way </Address> <City> Burnaby </City> <StateProvince> BC </StateProvince> <Country> Canada </Country> <ZipPostalCode> V5A 1B5 </ZipPostalCode> <Telephone> (604) 293-5753 </Telephone> <FAX> (604) 473-5807 </FAX>

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Profile Using Markup Profile Using Markup (cont.)(cont.) <Card> < Type > VISA </ Type > <Number> 123456789 </Number> <Expiry> 1200 </Expiry> </Card> <Card> <Type> AMEX </ Type > <Number> 987654321 </Number> <Expiry> 0401 </Expiry> </Card></Profile>



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eXtensible Markup LanguageeXtensible Markup Language• Extensible

– Tag set is not fixed• Structural

– Deep, hierarchical nesting of structures• Ordered lists (unordered with Schema)

– Can infer meaning from structure• Valid document requirement

– Can check structure against a schema• Well formed (DTDs and Schema)



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eXtensible Markup LanguageeXtensible Markup Language• Portable

– Text-based Unicode– All parsers must support UTF-8 (US-ASCII)– Parsers may support: UTF-16, EBCDIC, UCS-4,

ASCII, ISO 646, ISO 8859, Shift-JIS, EUC, etc• Human readable• Machine understandable• W3C standard

– Rich set of emerging tools



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XML Tooling: IE5XML Tooling: IE5



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Isn’t This Just Like HTML?Isn’t This Just Like HTML?• HTML is a markup language based on SGML• Key differences

– HTML has a fixed set of tags– HTML mixes stylistic, structural, and semantic

tags– HTML does not support deep nesting and

hierarchy– HTML is invalid

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XML IssuesXML Issues• XML documents must be valid


</Message>

Valid

Invalid<Message>

Hello, World!

Hello, World!</Message>


</MESSAGE>

• Means that structure can be inferred



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XML IssuesXML Issues• Knowledge of document organization• Distribution of document organization• Character set issues• Document focus• Parser speed and complexity



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Message Organization: DTDsMessage Organization: DTDs• Document Type Definition• Used to validate documents• Issues:

– Doesn’t use XML syntax, not extensible– Writing good DTDs is hard– Very awkward and limited language constructs,

uses eBNF grammar– No namespaces– No inheritance, defaults, ranges, enums

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Profile DTD ExampleProfile DTD Example<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE Profile [<!ELEMENT Profile (Name, Address, City, StateProvince, Country, ZipPostalCode, Telephone, FAX, Card*)><!ELEMENT Name (#PCDATA)><!ELEMENT Address (#PCDATA)> <!ELEMENT Card (Type, Number, Expiry)><!ELEMENT Type (#PCDATA)><!ELEMENT Number (#PCDATA)><!ELEMENT Expiry (#PCDATA)>]>

<Profile> <Name> K. Scott Morrison </Name> <Address> 8999 Nelson Way </Address>  <Card> <Type> VISA </Type> <Number> 123456789 </Number> <Expiry> 1200 </Expiry> </Card> </Profile>



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Message Organization: SchemaMessage Organization: Schema• Alternative to DTDs• XML syntax• Much more expressive• Has namespace support• Has inheritance, defaults, ranges

(min/max), enumerations, sequences, unordered lists

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Transforms: XSLTransforms: XSL<Profile> <Name> K. Scott Morrison </Name> <Address> 8999 Nelson Way </Address> <City> Burnaby </City> <StateProvince> BC </StateProvince> <Country> Canada </Country> <ZipPostalCode> V5A 1B5 </ZipPostalCode> <Telephone> (604) 293-5753 </Telephone> <FAX> (604) 473-5807 </FAX><Card> <Name> VISA </Name> <Number> 123456789 </Number> <Expiry> 1200 </Expiry> </Card> <Card> <Name> AMEX </Name> <Number> 987654321 </Number> <Expiry> 0401 </Expiry> </Card></Profile>

<VisaCard> <CardNumber> 123456789 </CardNumber> <Expiry> 1200 </Expiry> <Client> <Name> K. Scott Morrison </Name> <Telephone> (604) 293-5753 </Telephone></Client></VisaCard>

XSL Engine

Source Document

Destination Document



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eXtensible Stylesheet LanguageeXtensible Stylesheet Language• XSL=XSL Transforms (XSLT) +

Formatting Objects and Properties• Some basic XSLT functions:

– Insertion of static text (like templates)– Copy, discard, or rearrange source text– Compute new text from source

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XSLT Example: XML to HTMLXSLT Example: XML to HTML<?xml version="1.0"?><xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"><xsl:template match="/"> <html> <body> Address is: <xsl:value-of select="Profile/Address"/> Name is: <xsl:value-of select="Profile/Name"/> </body></html></xsl:template></xsl:stylesheet>

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XML as DataXML as Data<Profile> <ID> 123456789 </ID> <Name> K. Scott Morrison </Name> <Address> 8999 Nelson Way </Address> <Card> <Name> VISA </Name> <Number> 123456789 </Number> <Expiry> 1200 </Expiry> </Card></Profile>

ID Name Address123456789 K. Scott Morrison 8999 Nelson Way

ID Type Number Expiry123456789 VISA 123456789 1200Da

taba

se

XML-Db Extender

XML

Docu

men

t

Profi

le

Tabl

eCa

rd

Tabl

e

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XML as Data: MessagingXML as Data: Messaging

Message Infrastructure:• ebXML• SOAP• etc

Client System

Server SystemRDBM

S

Request XML Message

<…>

<…> …

</…></…>

<…>

<…> …

</…></…>

Response XML

MessageTransport Examples:• HTTP over sockets• MQSeries• etc

Message Formats:• OTA• TravelFrame• etc

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Schema DistributionSchema Distribution<…>

<…> …

</…></…>

XML Message

Source System

Destination System

<…>

<…> …

</…></…>

Schema Repository

<…>

<…> …

</…></…>

Embe

dded

Repl

icat

edCe

ntra

lized

DTD

DTD



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Applications: InteroperabilityApplications: Interoperability

S390

SNA

AS400s

S390

UNIX Servers

TCP/

IPGateway

Thick PC Clients



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Applications: InteroperabilityApplications: Interoperability

S390

MQSeries Integrator

routing and transforming

XML messages

AS400s

S390

UNIX Servers

Thick PC Clients



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Applications: eBusinessApplications: eBusiness

S390

SNA

AS400s

S390

Internet

Web/WML/XML

Servers

TCP/

IP



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SummarySummary• XML is here to stay• There will be heavy vendor support for it

because:1. XML is standardized2. XML will be the B2B message format

• It can be leveraged now in most domains

xml: the promise and the reality

Documents