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Chapter 17

Chapter 17. Client-Server Processing and Distributed Databases. Outline. Overview of Distributed Processing and Distributed Data Client-Server Database Architectures Web Database Connectivity Architectures for Distributed Database Management Systems

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Chapter 17

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  1. Chapter 17 Client-Server Processing and Distributed Databases

  2. Outline • Overview of Distributed Processing and Distributed Data • Client-Server Database Architectures • Web Database Connectivity • Architectures for Distributed Database Management Systems • Transparency for Distributed Database Processing • Distributed Database Processing

  3. Evolution of Distributed Processing and Distributed Data • Need to share resources across a network • Timesharing (1970s) • Remote procedure calls (1980s) • Client-server computing (1990s)

  4. Timesharing Network

  5. Resource Sharing with a Network of Personal Computers

  6. Client-Server Processing with Distributed processing only

  7. Distributed processing and data

  8. Motivation for Distributed Processing • Flexibility: the ease of maintaining and adapting a system • Scalability: the ability to support scalable growth of hardware and software capacity • Interoperability: open standards that allow two or more systems to exchange and use software and data

  9. Motivation for Distributed Data • Data control: locate data to match an organization’s structure • Communication costs: locate data close to data usage to lower communication cost and improve performance • Reliability: increase data availability by replicating data at more than one site

  10. Summary of Distributed Processing and Data

  11. Client-Server Database Architectures • Client-Server Architecture is an arrangement of components (clients and servers) among computers connected by a network. • A client-server architecture supports efficient processing of messages (requests for service) between clients and servers.

  12. Design Issues • Division of processing: the allocation of tasks to clients and servers. • Process management: interoperability among clients and servers and efficiently processing messages between clients and servers. • Middleware: software for process management

  13. Tasks to Distribute • Presentation: code to maintain the graphical user interface • Validation: code to ensure the consistency of the database and user inputs • Business logic: code to perform business functions • Workflow: code to ensure completion of business processes • Data access: code to extract data to answer queries and modify a database

  14. Middleware • A software component that performs process management. • Allow clients and servers to exist on different platforms. • Allows servers to efficiently process messages from a large number of clients. • Often located on a dedicated computer.

  15. Client-Server Computing with Middleware

  16. Types of Middleware • Transaction-processing monitors: relieve the operating system of managing database processes • Message-oriented middleware: maintain a queue of messages • Object-request brokers: provide a high level of interoperability and message intelligence • Data access middleware: provide a uniform interface to relational and non relational data using SQL

  17. Two-Tier Architecture

  18. Two-Tier Client-Server Architecture • A PC client and a database server interact directly to request and transfer data. • The PC client contains the user interface code. • The server contains the data access logic. • The PC client and the server share the validation and business logic.

  19. Three-Tier Architecture (Middleware Server)

  20. Three-Tier Architecture (Application Server)

  21. Three-Tier Architecture • To improve performance, the three-tier architecture adds another server layer either by a middleware server or an application server. • The additional server software can reside on a separate computer. • Alternatively, the additional server software can be distributed between the database server and PC clients.

  22. Multiple-Tier Architecture • A client-server architecture with more than three layers: a PC client, a backend database server, an intervening middleware server, and application servers. • Provides more flexibility on division of processing • The application servers perform business logic and manage specialized kinds of data such as images.

  23. Multiple-Tier Architecture

  24. Multiple-Tier Architecture with Software Bus

  25. Web Database Connectivity • Internet commerce depends heavily on database access for websites. • Web database connectivity allows a database to be manipulated through a Web page. • A user may use a Web form to change a database or view a report generated from a database.

  26. Internet Basics • Network of networks • Uses standard protocols: TCP/IP • TCP: splits messages into packets • IP: routes messages • Each computer on the Internet has a unique numeric address known as an IP address.

  27. Internet and Intranet Relationship

  28. World Wide Web • Most popular application on the Internet • Supports browsing pages located on any computer on the Internet • Hypertext Transport Protocol (HTTP) establishes a session between a browser and a Web server. • Each page has a unique address known as a URL.

  29. Web Page Request Cycle

  30. XML/XSL • Solutions to HTML limitations • eXtensible Markup Language (XML) • Separates content and structure of a document • Use document type declaration or schema to specify document structure • eXtensible Style Language (XSL): supports transformation into display languages • Both are extensible languages

  31. The Common Gateway Interface (CGI) • CGI is an interface that allows a Web server to invoke an external program on the same computer. • The external program uses the parameters passed by the Web server to produce output that is sent back to the browser. • Usually, the output contains HTML/XML so that the browser can display it properly.

  32. Straight CGI

  33. Hybrid CGI

  34. Server-side connectivity • Server-side connectivity bypasses the external program needed with the CGI approaches. • Specialized Web server or middleware server is needed • SQL statements and database logic are kept in a web page or external file. • The database code can execute stored procedures on the database server.

  35. Server-Side Connectivity Approach

  36. Server-Side Connectivity with a Middleware Server

  37. Client-Side Connectivity • Client computing capacity can be more fully utilized without storing code on the client. • Provides a more customized interface than permitted by HTML • Supports data buffering by the client to improve performance

  38. Web Page Request Cycle with Client-Side Connectivity

  39. Summary of Web Connectivity

  40. Architectures for Distributed Database Management Systems • DBMSs need fundamental extensions. • Underlying the extensions are a different component architecture and a different schema architecture. • Component Architecture manages distributed database requests. • Schema Architecture provides additional layers of data description.

  41. Global Requests

  42. Component Architecture

  43. Schema Architecture I

  44. Schema Architecture II

  45. Transparency for Distributed Database Processing • Transparency is related to data independence. • With transparency, users can write queries with no knowledge of the distribution, and distribution changes will not cause changes to existing queries and transactions. • Without transparency, users must reference some distribution details in queries and distribution changes can lead to changes in existing queries.

  46. Motivating Example

  47. Fragments Based on the CustRegion Field

  48. Fragments Based on the WareHouseNo Field

  49. Fragmentation Transparency • Fragmentation transparency provides the highest level of data independence. • Users formulate queries and transactions without knowledge of fragments (locations, or local formats). • If fragments change, queries and transactions are not affected.

  50. Location Transparency • Location transparency provides a lesser level of data independence than fragmentation transparency. • Users need to reference fragments in formulating queries and transactions. • However, knowledge of locations and local formats is not necessary.

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