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7 XML Web-Site Architectures

7 XML Web-Site Architectures. How (and why) to apply XML techniques in the implementation of Web sites ? 7.1 XML, Databases, and Multi-tiered Systems Overview of Web-based applications built using XML & database technology and multi-tiered architectures Later:

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7 XML Web-Site Architectures

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  1. 7 XML Web-Site Architectures • How (and why) to apply XML techniques in the implementation of Web sites? 7.1 XML, Databases, and Multi-tiered Systems • Overview of Web-based applications built using XML & database technology and multi-tiered architectures • Later: 7.2 Apache Cocoon publishing framework Notes 7: XML Web Sites

  2. 7.1 XML, Databases, and Multi-tiered Systems J. Chelsom, InterCHANGE, Oct. 1999, 7-12. • Why to use XML at a Web site? • How to store XML documents? • Multitiered architectures? Notes 7: XML Web Sites

  3. Advantages of XML based solutions? • Creating and delivering final document representations (HTML, PDF, …) more straightforward than using XML • Why then XML-based web sites? • control of uniform style (via style sheets) • processing of semantic content (XML) on the client • utilising XML processing capabilities on the server • tailoring different versions of the same content • for different browsers, different user groups, different uses (browsing, printing, audio, …) Notes 7: XML Web Sites

  4. XML and Databases • How to store and to manage XML documents? Depends on application requirements: • file system • simple and cheap • often sufficient, especially if collection small and static • database management systems • provide efficient access to large data collections • more appropriate when documents dynamically modified, especially if simultaneously by multiple users • provide consistency and integrity preserving "ACID" transactions Notes 7: XML Web Sites

  5. Database Transactions • Transaction • semantically meaningful unit of update operations • e.g., money transfer btw two bank accounts • ACID properties of transactions • Atomicity: either all changes or none are committed • Consistency: transactions maintain consistency of data • Isolation: transactions do not interfere with each other • Durability: committed updates are stored permanently Notes 7: XML Web Sites

  6. Types of XML databases 1. XML generating databases • database not aware of XML, which is just an output format for data extracted (using SQL/OQL/JSP/…) 2. XML document databases • fields for entire documents or document fragments • metadata fields to support management of these chunks 3. XML component databases • "true XML databases" • store document components as separate objects • schema for document objects corresponds to DTD Notes 7: XML Web Sites

  7. Commercial XML databases • Steve Pepper's "Whirlwind guide" of SGML/XML tools (Dec. 99) mentioned • 10 document DB managers; 1 with XML support • SigmaLink of STEP GmbH • 6 component DB managers, 3 with XML support • Astoria, POET Content Mgmt Suite, TARGET 2000 • strong development activity underway by major O-O and relational database vendors • Prizes of high-end XML database systems around USD 40,000 - 100,000 (including configuration, installation and integration to business processes) Notes 7: XML Web Sites

  8. Commercial XML databases (2) • Ronald Bourret,Nov. 2000: http://www.rpbourret.com/xml/XMLDatabaseProds.htm • 5 XML-enabled databases  XML generating/document databases • DB2 XML Extender, MS SQL Server 2000, Oracle 8i & 9i, … • 8 native XML databases  XML component databases (?)  3 RD prototypes, rest commercial products (?) • Also middleware, XML servers, XML application servers, content management systems, persistent DOM implementations: classification often difficult Notes 7: XML Web Sites

  9. Three-tiered architectures • Typical architecture of web-based data delivery/processing applications: • client tier (or layer) • standard web browser (+ possible additions) • middle tier / applications layer • "business logic" running on server • can be viewed or realised as number of separate tiers(-> "multitiered architectures") • data tier (or layer) • storage and maintenance of data Notes 7: XML Web Sites

  10. Why three-tiered architectures? • HTTP client + server + data source is a convenient implementation environment • familiar browser user-interface • standard components (browsers & servers) • cheap (free) • available on various OS & HW platforms • minimal start-up pain for new users or customers Notes 7: XML Web Sites

  11. Where XML gets processed? • Two major strategies: 1. to deliver XML to client • and to use, say, SAX/DOM-based applets or DOM-based scripts for processing, andCSS, or XSLT->HTML(+CSS) for presentation 2. to process XML on the server • and to deliver plain HTML (+CSS) to client • Which one to choose? Notes 7: XML Web Sites

  12. Delivering XML to web clients • Advantages: • single semantically marked-up XML document may correspond to multiple single-purpose HTML pages • reduces network traffic and moves processing load from server to client • Disadvantages • assumes XML capable browsers • application development for unknown client environments difficult Notes 7: XML Web Sites

  13. Delivering XML to web clients (2) • Disadvantages (continued) • exposure of data structures (XML) and "business logic" (applets or scripts) to customers • XML processing on client may be a viable solution in controlled environments like intranets (clients uniform, users trusted) • "XML on server, HTML to client" strategy gained more popularity recently Notes 7: XML Web Sites

  14. Processing XML on server • plain HTML delivered to clients • Advantages: • support of non-XML-capable browsers • (Next section discusses taking of different HTML browsers into account) • ability to address wider audiences • "semantic firewall" • document structures and business logic remain unexposed • control over processing environment (server) • easier application development and testing • control over performance Notes 7: XML Web Sites

  15. Processing XML on server (2) • Disadvantages: • may increase data traffic: a new HTML page for each different view on the document • fails to utilise (often idle) processing cycles of client computers • heavier network and server load • Combinations of client/server processing also possible: Delivering • "downgraded" XML to clients • XML to selected clients only Notes 7: XML Web Sites

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