L09 - E x tensible M arkup L anguage CS174A: XML 2...

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Unformatted text preview: E x tensible M arkup L anguage CS174A: XML 2 “Data” on the Web ¡ HTML documents – often generated by applications – consumed by humans only – easy access: across platforms, across organizations ¡ No application interoperability: – HTML not understood by applications ¡ screen scraping brittle – Database technology: client-server ¡ still vendor specific CS174A: XML 3 Paradigm Shift on the Web ¡ From documents (HTML) to data (XML) ¡ From information retrieval to data management ¡ For databases, also a paradigm shift: – from relational model to semi-structured data – from data processing to data/query translation – from storage to transport CS174A: XML 4 An Application Framework ¡ Information integration : Making databases from various places work as one ¡ Semi-structured data: A new data model designed to cope with problems of information integration ¡ XML : A standard language for describing semi- structured data schemas and representing data CS174A: XML 5 The Information-Integration Problem ¡ Related data exist in many places and could, in principle, work together ¡ But different databases differ in: – Model (relational, object-oriented?) – Schema (normalized/unnormalized?) – Terminology: are consultants employees? Retirees? Subcontractors? – Conventions (meters versus feet?) CS174A: XML 6 Examples ¡ Every bar has a database – One may use a relational DBMS; another keeps the menu in an MS-Word document – One stores the phones of distributors, another does not – One distinguishes ales from other beers, another doesn ’ t – One counts beer inventory by bottles, another by cases CS174A: XML 7 ¡ Warehousing : Make copies of the data sources at a central site and transform it to a common schema – Reconstruct data periodically (daily, weekly, …), but do not try to keep it more up-to-date than that ¡ Mediation : Create a view of all sources, as if they were integrated – Answer a view query by translating it to terminology of the sources and querying them Two Approaches to Integration CS174A: XML 8 Warehouse Diagram Warehouse Wrapper Wrapper Source 1 Source 2 User query Result CS174A: XML 9 A Mediator Mediator Wrapper Wrapper Source 1 Source 2 User query Query Query Query Query Result Result Result Result Result CS174A: XML 10 Semi-Structured Data ¡ Purpose: represent data from independent sources more flexibly than either relational or object- oriented models ¡ Think of objects, but with the type of each object its own business, not that of its “ class ” ¡ Labels to indicate meaning of substructures CS174A: XML 11 Graphs of Semi-structured Data ¡ Nodes = objects ¡ Labels on arcs (attributes, relationships) ¡ Atomic values at leaf nodes (nodes with no arcs out) ¡ Flexibility: no restriction on – Labels out of a node – Number of successors with a given label CS174A: XML 12 Example: Data Graph Bud A.B....
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This note was uploaded on 05/02/2010 for the course CS 174a taught by Professor Zhin during the Fall '09 term at UCSB.

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L09 - E x tensible M arkup L anguage CS174A: XML 2...

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