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XML, Java, and the future of the Web Jon Bosak, Sun Microsystems Last revised 1997.03.10 Presented and Annotated by Byung-Hoon Kang ([email protected]) RoadMap : Part1: Why XML ? Part2: Example applications HTML and SGML SGML and XML SGML vs. XML vs. HTML 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 HTML and SGML SGML allows documents to describe their own grammar HTML hardwires a small set of tags: a single SGML specification HTML Extensibility: new tag ? application change? Yes Needed SGML Yes Independent Structure: deep nested ? No Yes Validation: structural validity ? No Yes 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 SGML’s extensibility, structure, and validation DTD is optionally needed for validation SGML vs. XML vs. HTML HTML Yes/No SGML XML Yes Yes Extensibility: new tag ? 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 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 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. 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. 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. 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 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 ? 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 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. 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 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 ? XML CSS need to be used to style HTML documents XSL, on the other hand, is able to transform documents CSS For example, XSL can be used to transform XML data into HTML/CSS documents Both languages can be used to style XML documents 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