Jon Bosak, Sun Microsystems Last revised XML, Java, and the future of the Web Presented and Annotated by Byung-Hoon Kang

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

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

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

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

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

XML applications : envisioned in 1997 ä ä to mediate between two or more heterogeneous databases. ä ä to distribute a significant proportion of the processing load from the Web server to the Web client. ä ä to present different views of the same data to different users. ä ä to tailor information discovery to the needs of individual users.

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

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

Why solution is not feasible in HTML ? ä ä HTML tag set is too limited ä ä to represent or differentiate between the multitude of database fields ä ä hard to automate the process ä ä HTML is incapable of representing the variety of structures in those documents. ä ä HTML lacks mechanism in checking the data for structural validity

XML solution envisioned in 1997 ä ä 1. Form a standards consortium for Health Care Markup Language and its HCML.DTD ä ä 2. Adopt a single industry-wide interchange format that serves as the single output format. ä ä 3. Use any standard application to validate and process HCML marked-up data with HCML.DTD ä ä Similar to the steps in traditional SGML usage ä ä Still have the same problem of standardization. ä ä Is XML advantageous than SGML in doing steps 1, 2 or 3 ?

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

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

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

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

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