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354.ServerEnvironment

354.ServerEnvironment - Database Systems I SQL in a Server...

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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 1 Database Systems I SQL in a Server Environment
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 2 Introduction So far: interactive SQL interface, pure “SQL programs”. In practice often: queries are not ad-hoc, but programmed once and executed repeatedly, need the greater flexibility of a general- purpose programming language, especially for complex calculations (e.g. recursive functions) and graphic user interfaces. SQL statements part of a larger software system
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 3 The Three-Tier Architecture The following three-tier architecture is common for database installations: Web servers connect clients to the DBS, typically over the Internet ( web-server tier ). Applications servers perform the “business logic” requested by the webserves, supported by the database servers ( application tier ). Database servers execute queries and modifications of the database for the application servers ( database tier ).
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 4 The Three-Tier Architecture Multiple processes can be run on the same processor. E.g., web server, application server and database server all on the same processor. This is common in small systems. In large-scale systems, however, there are usually many processors running processes corresponding to the same “server”, i.e. the same program. For example, many processors running application server processes and other processors running web server processes.
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 5 The Three-Tier Architecture Database Server DB Database Server Application Server Application Server Application Server Web Server Web Server Web Server Web Server Client Client Client Client Client Internet
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 6 The Web-Server Tier When a user makes a request on the Internet, a web server responds. The user becomes a client of that server. Example Amazon.com User enters www.amazon.com in browser. Web server presents Amazon homepage. User enters book title and starts search. The web server responds to the user request, using the services of an application server.
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 7 The Application Tier The application tier receives requests from the web-server tier and turns data from the database tier into answers to web server requests. Example Amazon.com Web server requests book with given title from application server. Application server sends corresponding SQL query to database server. Database server returns a (set of) tuple(s). Application server assembles the resulting tuple(s) into an HTML page and sends it to the web server.
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 8 The Database Tier The database tier execute queries issued by the application tier and returns the corresponding results to the application tier.
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