The eXtensible Markup Language: An Introduction to XML Documents

Spring 2000

The eXtensible Markup Language: An Introduction to XML Documents & Databases

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Christophides Vassilis

Spring 2000

Preliminary Issues

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What is a document?

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Content: the components (words, images etc). which make up a document Structure: the organization and inter-relationship of the components Presentation: how a document looks and what processes are applied to it

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Separating these things means... ●

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●

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The content can be re-used ◆ for printing ◆ for querying ◆ for exchanging The structure can be formally validated The presentation can be customized for ◆ different media ◆ different audiences … in short, the information can be uncoupled from its processing

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Documents vs Databases Document world ●

plenty of small documents ◆ usually

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implicit structure

●

●

◆ machine ●

◆ data, ●

methods

paradigms

as”, WYSIWYG name, date, subject

friendly

content

◆ Data

Independence, Transaction Management, Query Languages

metadata ◆ author

types

records

annotation

paradigms

dynamic

explicit structure ◆

●

content

◆ “Save

◆ usually

friendly

◆ form/layout, ●

a few large databases

paragraph, toc,

tagging ◆ human

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static

◆ section, ●

Database world

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metadata ◆ schema

description

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DBMS ANSI/SPARC Architecture (;7(51$/ /(9(/ VIEW 1

VIEW 2

VIEW 3

INTEGRATION &21&(378$/ /(9(/

LOGICAL SCHEMA PHYSICAL SCHEMA Christophides Vassilis

,17(51$/ /(9(/ 6

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What to do with them Database

Documents ●

editing

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updating

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spell-checking

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cleaning

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counting words ●

querying

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composing/transforming

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retrieving (IR)

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printing

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Query Languages Document Retrieval Claude Monet DQG San Diego Museum of Art

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Database Querying VHOHFW p IURP Artists a, a.artwork p ZKHUH a.first = “Claude” DQG a.last = “Monet” DQG p.located = “San Diego Museum of Art”

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The Long Road of Document Standards

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 Rick Jelliffe 1999

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What’s Wrong with HTML ●

If written properly, normal HTML may reflect document presentation, but it cannot adequately represent the semantics & structure of data

$UWLVW1DPH

$UWLIDFW7LWOH

%!021(7&ODXGH%!%5! +D\VWDFNVDW&KDLOO\DW6XQULVH%5! 'DWH %5! 'LPHQVLRQV 2LORQFDQYDV%5! 0DWHULDO [FP[LQ %5! ,PDJH 6DQ'LHJR0XVHXPRI$UW%5! 5HIHUHQFH 0XVHXP 3! ,0*65& ³KWWSDUWFKLYH PPRQHWKD\ULFNVMSJ´!

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HTML Document Presentation vs. …

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… XML Data Representation ●

A possible XML markup of the same information will retain the structure (and the semantics) of the various data objects

ClaudeMonet Haystacks at Chailly at Sunrise 1865 Oil on canvas 3060 11 7/823 3/4 San Diego Museum of Art Christophides Vassilis

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XML can be Published as normal Web Data

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What is XML? ●

Markup Meta-Language for domain or application specific structured documentation ◆ Mathematical,

●

chemical, musical, publishing, etc.

Developed by the SGML Editorial Board formed under the auspices of the World Wide Web Consortium (W3C) ◆ Founded

in 1996 by Jon Bosac (Sun) and various Web/SGML vendors: Textuality, Netscape, Microsoft, INSO, HP, Highland, NCSA, ArbortText, GRIF, SoftQuand

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Subset of SGML optimized for use in the Inter/Intranet ◆ SGML

is proving difficult to implement for Web/Intranet applications ◆ SGML has been hard to cost-justify to management ●

Opens the way for a new generation of Web applications ◆ Improve precision during searching and retrieval ◆ Enable multiple usage of the same data ◆ Facilitate distributed processing with more versatile

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ways to manipulate data 14

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Why XML? ●

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XML provides key features for a new generation of Web applications: ◆ Structuring: unlike HTML it preserves the structure of the data ◆ Extensibility: not a fixed format like HTML but user-oriented tagging ◆ Validation: provides the means to consuming applications to check data for structural validity on importation ◆ Presentation Late Binding: describes data, not visual presentation ◆ Human Readable: similar to HTML ◆ Interchange: good for transmission of data from server to browser, and from application to application, or machine to machine ◆ Open standard: non proprietary format XML becomes an integral part of the Web infrastructure ◆ Microsoft Explorer (V5.0) already offers XML browsing ◆ Ongoing XML implementation by Netscape ◆ Various XML middleware and manipulation tools 15

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The XML Language Family ●

XML (Extensible Markup Language) ◆A

subset of SGML (ISO 8879) designed for easy implementation

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XLink (Extensible Linking Language) ◆A

set of standard hypertext mechanisms based on HyTime (ISO/IEC 10744) and the Text Encoding Initiative (TEI)

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XSL (Extensible Stylesheet Language) ◆A

standard stylesheet language for structured information derived from DSSSL (ISO/IEC 10179) and key CSS concepts

Christophides Vassilis

∆τ N $ 35 0 30 0 25 0 20 0 15 0

Ta gs A t tribu te

10 0

50

0

HTML 0. 0

TEI L ite 1. 6

IB M ID Doc 4. 0

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Interrelationships Among the Various W3C Efforts

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XML Syntax and Semantics

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An Example of XML Markup (OHPHQW1DPH (OHPHQW&RQWHQW Claude Monet Haystacks at Chailly at Sunrise $WWULEXWH1865 Oil on canvas $WWULEXWH9DOXH 1DPH 3060 11 7/823 3/4 San Diego Museum of Art (PSW\(OHPHQW Christophides Vassilis

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The Logical Tree Structure of XML ARTIST NAME

ARTWORK

FIRST

LAST

ARTIFACT

&ODXGH

021(7

TITLE

DATE

DIM

DIM

H W

H W

+D\VWDFNV 

IMAGE KD\ULFNVMSJ

      2LORQFDQYDV MATERIAL Christophides Vassilis

6DQ 'LHJR LOCATION 0XV

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XML Document Type Definitions '2&7 (/(0(17DUWLVWQDPHERUQGHDWKDUWZRUNQDWLRQDOLW\"LQIOXHQFHV ! $77/,67DUWLVWRLG,'5(48,5('[POODQJ1072.(1,03/,('! (/(0(17QDPHILUVWODVW ! (/(0(17ILUVW3&'$7$ ! (/(0(17ODVW3&'$7$ ! (/(0(17DUWZRUNDUWLIDFW ! (/(0(17DUWIDFWWLWOHGDWHPDWHULDOGLP ORFDWLRQLPDJH ! (/(0(17WLWOH3&'$7$ ! (/(0(17GLPKHLJKWZLGWK ! $77/,67GLPPHWULFFP_LQ µFP¶! (/(0(17ORFDWLRQ3&'$7$ ! (/(0(17LPDJH(037
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Mixed models must be optional repeatable OR-groups, with #PCDATA first 23

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What XML can express? ●

Sequence « , » (/(0(17QDPHILUVWODVW !

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Choice « | » (/(0(17PHGLDLPDJH_YLGHR !

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Option ( 1 or 0 ) « ? » (/(0(17DUWLVW«QDWLRQDOLW\"«

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Repetition (1 or more ) « + » (/(0(17DUWZRUNDUWLIDFW !

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Option and Repetition ( 0, 1 or more ) « * » (/(0(17DUWIDFWGLP  !

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XML Content Models and Regular Expressions ●

Each element content model is defined by a regular expression ◆ Example: QDPHDGGU HPDLO

●

Each regular expression determines a corresponding finite state

automaton ●

This suggests a simple parsing program

DGGU QDPH ●

HPDLO

Content Models should be defined by unambiguous regular expressions 25

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XML Regular Expressions: Another Example ●

Adding in the optional greet further complicates things ◆ Example: name,address*,(tel | fax)*,email*

DGGUHVV QDPH

HPDLO

WHO WHO

HPDLO

ID[ ID[

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HPDLO

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Definition of Attribut’s Content (value1 | value2 | .. |valuen) value enumeration CDATA string of valid XML character data

$77/,67GLPPHWULFFP_LQ ! GLPPHWULF µLQ¶! $77/,67UHIKUHI&'$7$! UHIKUHI µKWWS DUWFKLYHPPRQHW[PO¶! $77/,67DUWLVWRLG,'! DUWLVWRLG 0RQHW! $77/,67DUWLIDFWFUHDWRU,'5()! DUWLIDFWFUHDWRU 0RQHW!

ID symbolic identifier of an element IDREF(S) reference (or list of) to element’s identifiers ENTITY(IES) $77/,67LPDJHILOH(17,7
More types (e.g., DATE) may soon be part of the standard 27

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Attribute Default Values ●

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Value µYL¶ ◆ a given value from an enumeration of values ),;(' value ◆ the value is the only possible instance for the attribute 5(48,5(' ◆ the value must be supplied ,03/,(' ◆ the value can be optionally supplied

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XML Entities ●

Entities allow the definition of short strings to stand for more complex information, which can reside inside or outside the document or its DTD

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Used for substitutions of data or markup: ◆ DTD

level e.g., markup declaration (Parameter entity)

◆ Document ●

level e.g., data and markup instances (General entity)

Used for references to external data or markup sources: ◆ the

content of the entity can be found using an XML system-specific storage location (Specific entity)

◆ the

content of the entity can be found by mapping a public identifier to a system-specific storage location (Public entity)

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XML Parameter Entities ●

Parameter entities are used for extensible declarations (e.g., macros) of complex content models or attributes in a DTD (17,7 42

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Mapping Between XML and Objects

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XML vs Relational DBMS SURMHFWV WLWOHEXGJHWPDQDJHG%\

HPSOR\HHV QDPHVVQDJH

'2&7 (/(0(17GE SURMHFWVHPSOR\HHV ! (/(0(17SURMHFWVSURMHFW ! (/(0(17HPSOR\HHVHPSOR\HH ! (/(0(17SURMHFWWLWOHEXGJHWPDQDJHG%\ ! (/(0(17HPSOR\HHQDPHVVQDJH !  @!

Christophides Vassilis

'2&7 (/(0(17GESURMHFW_HPSOR\HH ! (/(0(17SURMHFWWLWOHEXGJHWPDQDJHG%\ ! (/(0(17HPSOR\HHQDPHVVQDJH !  @!

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Recursive DTDs '2&7 (/(0(17JHQHDORJ\SHUVRQ ! (/(0(17SHUVRQQDPH GDWH2I%LUWK SHUVRQPRWKHU SHUVRQIDWKHU !  @! ●

What is the problem with this? 45

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Recursive DTDs cont’d. '2&7 (/(0(17JHQHDORJ\SHUVRQ ! (/(0(17SHUVRQQDPH GDWH2I%LUWK SHUVRQ"PRWKHU SHUVRQ" !IDWKHU  @! ●

What is now the problem with this?

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Some Things are Hard to Specify ● Each employee element is to contain name, age and ssn elements in some order

(/(0(17HPSOR\HH QDPHDJHVVQ _DJHVVQQDPH _VVQQDPHDJH _« ! ●

Suppose there were many more fields !

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Specifying ,' and ,'5()Attributes '2&7 (/(0(17IDPLO\SHUVRQ ! (/(0(17SHUVRQQDPH ! (/(0(17QDPH3&'$7$ ! $77/,67SHUVRQLG,'5(48,5(' PRWKHU,'5(),03/,(' IDWKHU,'5(),03/,(' FKLOGUHQ,'5()6,03/,('! @!

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Some Conforming XML data IDPLO\!  SHUVRQLG MDQHPRWKHU PDU\IDWKHU MRKQ!  QDPH!-DQH'RHQDPH!  SHUVRQ!  SHUVRQLG MRKQFKLOGUHQ MDQHMDFN!  QDPH!-RKQ'RHQDPH!  SHUVRQ!  SHUVRQLG PDU\FKLOGUHQ MDQHMDFN!  QDPH!0DU\'RHQDPH!  SHUVRQ!  SHUVRQLG MDFNPRWKHU ´PDU\IDWKHU MRKQ!  QDPH!-DFN'RHQDPH!  SHUVRQ! IDPLO\! Christophides Vassilis

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An Alternative XML DTD Specification '2&7 (/(0(17IDPLO\SHUVRQ ! (/(0(17SHUVRQPRWKHU"IDWKHU"FKLOGUHQQDPH ! $77/,67SHUVRQLG,'5(48,5('! (/(0(17QDPH3&'$7$ ! (/(0(17PRWKHU(037
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The Revised XML Data IDPLO\!  SHUVRQLG MDQH´! QDPH!-DQH'RHQDPH!  PRWKHULGUHI PDU\´!PRWKHU!  IDWKHULGUHI MRKQ!IDWKHU! SHUVRQ!  SHUVRQLG MRKQ´! QDPH!-RKQ'RHQDPH! FKLOGUHQLGUHIV MDQHMDFN!FKLOGUHQ!  SHUVRQ!  IDPLO\! 51

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Mapping between XML and Tables

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Bluring the Frontiers between Data & Documents

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Towards XML-enabled DBMS ●

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Xml-enabled database system ◆ Store XML data/documents into the database server ◆ Query and search valid and wellformed XML ◆ Generate XML data from the database server ◆ Add XML capabilities in supporting database facilities XML has the potential to impact four important markets ◆ Web integration ◆ Web publishing ◆ Application integration ◆ Electronic commerce

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DBMS Integrate with other facilities Generate XML Store XML

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Storing XML Data ●

Enhance XML storage facilities in the database: ◆ Utilities to load XML data into the database ◆ Provide more efficient database storage (componentized storage, compression, indexing,…) ◆ XML export tools from the server ◆ Allow server-to-server replication of XML data

Database HTML HTML XML

Database 55

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Querying and Searching XML Data

●

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Fine-grained access to XML documents Search XML data efficiently ◆ Special SQL queries over valid + well-formed XML ◆ Content-based indexing (e.g. Text indexes) for searching XML data efficiently ◆ Support for XML query languages (e.g. XQL) on XML data

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Database

HTML HTML XML

Web 56

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Generating and Manipulating XML ●

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Generate XML from the database server ◆

Map ODMG, SQL92, SQL3 and PL/SQL datatypes to XML

◆

Provide mappings between java, SQL and XML types

Script XML content from the database ◆ Allow SQL queries to return XML results ◆ Provide embedded XML in stored procedures ◆ Java scripting: support embedded XML in java ◆ Common APIs to access any XML content in databases

Web

HTML XML

Database

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Database X

Database Y XML

XML Total

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XML

XML Sorted

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Epilogue

● ● ● ● ●

1960’s: Data Centric 1970’s: Process Centric 1980’s: Object Oriented 1990’s: Component Based 2000’s: XML?

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Data was our First Focus

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Then we Focused on Logic

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Object Oriented Programming Focused on Runtime Behavior ‡&RPPRQ7HUPVIRU $QDO\VLVDQG'HVLJQ ‡7LJKWO\&RXSOHG&RGH ¶V 'DWD

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Component Programming Shifted the Focus to Interfaces

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Spring 2000

XML Returns the Focus to Data

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BIBLIOGRAPHY ●

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Charles F. Goldfarb, Paul Prescod, Paper Michael, Leventhal, et al. “The XML Handbook”. Printice Hall, 1998. David Megginson. “Structuring XML Documents”. Printice Hall, 1998. Simon St. Laurent. “XML : Extensible Markup Language”. IDG Books, 1998. Rick Jelliffe. “The XML and SGML Cookbook : Recipes for Structured Information”. Printice Hall, 1998. Simon St. Laurent. “Xml : A Primer”. IDG Books, 1998. Steven Holzner. “XML Complete”. McGraw-Hill, 1997. Richard Light, Tim Bray. “Presenting Xml”. Macmillan Publishing, 1997. Bryan Pfaffengerger. “Web Publishing With XML in Six Easy Steps”, 1997. Steven J. DeRose. “The SGML FAQ Book : Understanding the Foundation of HTML and XML”. Kluwer Academic Publishers, 1997. Sean McGrath. “XML by Example: Building E-Commerce Applications”. Printice Hall, 1998 Charles F. Goldfarb, Steve Pepper, Chet Ensign. “SGML Buyer’s Guide : A Unique Guide to Determining Your Requirements and Choosing the Right SGML and XML Products and Services”. Printice Hall, 1998. 65

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