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Web Data Bases

Web Data Bases. Reference Ozsu. Web Applications. Web Applications which access the databases through web browsers at the client side Three Tier Architecture Usually the databases are in relational model Information Integration from multiple sources distributed over WWW

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Web Data Bases

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  1. Web Data Bases Reference Ozsu

  2. Web Applications • Web Applications which access the databases through web browsers at the client side • Three Tier Architecture • Usually the databases are in relational model • Information Integration from multiple sources distributed over WWW • Mediator Wrapper Architecture • Hierarchical mediator Architecture • The datasources are either • fully unstructured (text and image data) • Fully Structured (Relational Data) • Semi Structured (HTML, SGML documents)

  3. Three Tier Architecture Client Server Database Server Web Browser Application Database Queries Tuples Client Server Middle ware Database Queries Database Server URL + user Input Web Browsers Application Servers Tuples HTML Forms Server Database Server Middle ware Client Query Calls Database Queries Web Browsers URL + user Input Database Gateway Web Servers Database Server Tuples HTML Forms HTML Forms

  4. Semi Structured Data • Structured Data • Relational Data – fully structured • HTML, SGML, XML – partially structured • Un structured Data • Text, Images

  5. Object Exchange Model • Popular model for representing semistructured data is a OEM graph • Where each node contains an object with the following information • Object Name • Type • Value • Object Reference • Each edge represents the relation ship that exists among the objects

  6. Relational Model Vs OEM • The data and the schema are separate in RM • The data is self explanatory. It contains information about its objects and their relation ships

  7. HTML Vs SGML • HTML is a mark up language which is used to define the physical structure of a document as it is viewed in a browser • SGML is a grammar which provides the platform to define various mark up languages • XML is like SGML which allows defining data in a semi structured form giving them logical structure with the help of DTDs

  8. Mediator Wrapper Architecture • Is used for accessing • Accessing large number of multiple data sources across www • Dynamic Data Sources which must be added or dropped without affecting the integrated view • Data sources have different computing capabilities from full –featured DBMS to simple files

  9. Mediator Wrapper Architecture • Wrapper • Is provided over each datasource • It provides information about the schema, query capabilities of the data source • Mediator • It gathers information from various wrappers and builds a unified view called global dictionary of directories • It also splits the queries and passes them to the respective queries • It composes the results from the results obtained from multiple sources

  10. Mediator Wrapper Architecture Wrappers Data Source Partial Queries Client Mediator URL + user Input Partial Result Web Browsers Unified View Global Data Dictionary Wrappers Data Source HTML Forms Partial Queries Partial Result

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