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Web Data Bases

This article explores the architecture of web applications that access databases through browsers, emphasizing three-tier architecture. It discusses the integration of structured, semi-structured, and unstructured data from diverse sources on the web. The mediator-wrapper architecture is examined, detailing how wrappers provide access to various data sources and how mediators create a unified view from multiple data outputs. The differences between relational models and object exchange models (OEM) are also highlighted, showcasing the significance of data schemas in forming structured and semi-structured information.

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Web Data Bases

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Presentation Transcript

  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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