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Server-Side Web Programming

with Active Server Pages

Introduction

Dynamic Web Content

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Web originally consisted of static content.

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Increasingly sophisticated uses of web rely ondynamically generated content.

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Dynamic content is not fixed - site content orfunctionality changes because of:^ – User input (forms)– Database content– Personalization– Where user came from– Other factors

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Sounds easy? Not!

Server-Side Dynamic Web

Content

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Programming server-side dynamic content for theweb is complex because:^ – The web is a client/server environment—

implementation “issues” are distributed…

• The web is based on the HTTP protocol, which does

not maintain user state between actions. (more later)

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Deeply understanding and applying these conceptsis where the “big money” is…

Client/Server Architecture

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Client/Server computing involves “clients”requesting and receiving services (e.g., files,printing, web) from “servers”.

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The web is intrinsically client/server—a user’sbrowser requests/receives a web page from awebserver.

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Although a “client” is typically a user’s PC orworkstation, a server can also be a “client” ofanother server (e.g., webserver requesting datafrom a database server).

Client/Server: Servers

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Servers are normally permanent, fixed resources. If theyare on the Internet, they have the same fixed IP address.

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Servers run operating systems such as Windows NT orLinux that are multitasking and can run unattended forlong periods.

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Server hardware is different from PCs or Macs. Serverhardware is designed to support multiple users and to be onall the time.

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Many sites use redundant server hardware so that theservices they provide are available all of the time.

Client/Server Architecture

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Programs/applications can be architected forclient/server environment.

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Client/server applications are a logical extensionof modular programming--separation of a largepiece of software into parts ("modules") cansimplify development via reuse and centralizedmaintenance.

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Client/server applications can be classified by howthey are distributed--these are called layers.

Layers and Tiers

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Layers are an abstract, generalized model. Tiers are theactual physical implementation of a client/serverapplication.

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Storage layer is critical for professional applications.Transactions on the storage layer must support ACID:^ –

ATOMICITY: Transaction should be done or undone completely. In theevent of failure, data should rollback to previous state.

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CONSISTENCY: Transaction should transform a system from oneconsistent state to another consistent state.

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ISOLATION: each transaction should happen independently of othertransactions occurring at the same time.

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DURABILITY: Completed transactions should remain permanent, evenduring system failure.

Client/Server Application Tiers

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One Tier^ – All the layers are on one computer (e.g., a FoxPro or

MS Access application).

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Two tier^ – The user interface and business logic reside on the

workstation and the data on the network (e.g., a VBapplication against a SQL*Server database).

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N-Tier^ – Each layer resides on different machines. In some

cases, multiple servers can involved (e.g., ASP webpage on webserver queries database and GIS servers.).