Jon%20Bosak,%20Sun%20Microsystems%20Last%20revised%201997.03.10

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XML, Java, and the future of the Web

• Jon Bosak, Sun MicrosystemsLast revised
  1997.03.10

Presented and Annotated by Byung-Hoon
Kang (hoon_at_cs.berkeley.edu)
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RoadMap

• Part1 Why XML ?
• HTML and SGML
• SGML and XML
• SGML vs. XML vs. HTML
• Part2 Example applications
• Example applications envisioned in 1997
• Database interchange problem
• Why solution is not feasible in HTML
• XML solution envisioned in 1997
• Part3 Why CSS/XSL ?
• What are style sheet and why?
• Style sheet languages
• Why two style sheets language for XML ?
• Conclusion XML,DTD,CSS and XSL

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HTML and SGML

• SGML allows documents to describe their own
  grammar
• HTML hardwires a small set of tags a single SGML
  specification
• 
  HTML SGML
• Extensibility new tag ? Yes
  Yes
• application change? Needed
  Independent
• Structure deep nested ? No
  Yes
• Validation structural validity ? No
  Yes

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SGML and XML

• SGML
• Contains many optional features not needed for
  Web applications
• Cost/benefit ratio unattractive to current
  vendors of Web browsers
• DTD is required all the time
• XML
• A simplified subset of SGML for Web applications
• Retain SGMLs extensibility, structure, and
  validation
• DTD is optionally needed for validation

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SGML vs. XML vs. HTML

• 
  HTML SGML XML
• Extensibility new tag ? Yes/No
  Yes Yes
• Structure deep nested ? No
  Yes Yes
• Validation structural validity ? No
  Yes Yes
• DTD is required for parsing ? No
  Yes Opt.
• Browser dependency ? High
  Low Low
• Cost/Benefit ?
  Good Poor Med
• When were you born ? 92
  86 98

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RoadMap

• Part2 Example applications
• Example applications envisioned in 1997
• Database interchange problem
• Why solution is not feasible in HTML
• XML solution envisioned in 1997
• Part3 Why CSS/XSL ?
• What are style sheet and why?
• Style sheet languages
• Why two style sheets language for XML ?
• Conclusion XML,DTD,CSS and XSL

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XML applications envisioned in 1997

• to mediate between two or more heterogeneous
  databases.
• to distribute a significant proportion of the
  processing load from the Web server to the Web
  client.
• to present different views of the same data to
  different users.
• to tailor information discovery to the needs of
  individual users.

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Database interchange the universal hub

• The information tracking system for a home health
  care agency
• Need to key-in all of patient medical histories
  and billing data from a variety of doctors,
  hospitals, pharmacies, and insurance companies.
• 1. Log into the hospital's Web site.
• 2. Become an authorized user.
• 3. Access the patient's medical records using a
  Web browser.
• 4. Print out the records from the browser.
• 5. Manually key in the data from the printouts.

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Database interchange the universal hub

• A real solution would look more like this
• 1. Log into the hospital's Web site.
• 2. Become an authorized user.
• 3. Access the patient's medical records in a
  Web-based interface that represents the records
  for that patient with a folder icon.
• 4. Drag the folder from the Web application over
  to the internal database application.
• 5. Drop it into the database.

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Why solution is not feasible in HTML ?

• HTML tag set is too limited
• to represent or differentiate between the
  multitude of database fields
• hard to automate the process
• HTML is incapable of representing the variety of
  structures in those documents.
• HTML lacks mechanism in checking the data for
  structural validity

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XML solution envisioned in 1997

• 1. Form a standards consortium for Health Care
  Markup Language and its HCML.DTD
• 2. Adopt a single industry-wide interchange
  format that serves as the single output format.
• 3. Use any standard application to validate and
  process HCML marked-up data with HCML.DTD
• Similar to the steps in traditional SGML usage
• Still have the same problem of standardization.
• Is XML advantageous than SGML in doing steps 1, 2
  or 3 ?

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RoadMap

• Part3 Why CSS/XSL ?
• What are style sheet and why?
• Style sheet languages
• Why two style sheets language for XML ?
• Conclusion XML,DTD,CSS and XSL

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What are style sheets and Why?

• Style sheets
• Describe how documents are presented on screens,
  in print or in audio.
• Detach the formatting information from data
  source in document
• Why want to influence the presentation of
  documents
• without sacrificing device-independence or
• adding new HTML tags.

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Stylesheets

• DSSSL (Document Style Semantics and Specification
  Language) for SGML
• DSSSL-online the subset of DSSSL for SGML
  online.
• CSS (cascading style sheets)
• provides a style mechanism well suited to the
  relatively low-level demands of HTML
• currently used a little bit
• XSL (extensible style language)
• needed to present XML document on the browser.
• transformational functionality

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Why two Style Sheet languages?

• CSS
  XSL
• Can be used with HTML? yes no
• Can be used with XML ? yes yes
• Transformation language? no yes
• Syntax ? CSS XML
• CSS need to be used to style HTML documents
• XSL, on the other hand, is able to transform
  documents
• For example, XSL can be used to transform XML
  data into HTML/CSS documents
• Both languages can be used to style XML documents

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Conclusion XML, DTD, CSS and XSL

• To validate XML structural input DTD
• To exchange data using XML None or DTD for
  structural validation
• To standardize the data exchange model Still
  need to form a consortium
• To render XML in XML-support-browser CSS or XSL
  
• To render XML in HTML-support-browser Use XSL
  to transform XML into HTML/CSS