1. Understanding Distributed Information Systems Sanjoy Sanyal (Tech for NonGeek)

2. Layers of an Information System Sanjoy Sanyal (Tech for NonGeek) Client Presents Information to External Entities E.g. a graphical user interface, module that formats a data set Presentation Layer Application Layer Implements the operation requested by the client thru the presentation layer Also referred to as the services of the information system. For e.g. when a client requests withdrawal from a banking account, the services include taking the request, checking balances and withdrawal limits, creating log entry, debiting the and approval for handing over money Resource Management Layer Deals with and implements the Data sources For e.g. databases, filesystems or other information repositories Information System

3. Top Down Design of an Information System Sanjoy Sanyal (Tech for NonGeek) Client Define presentation formats and protocols for selected clients Presentation Layer Application Layer Define the functionality necessary to deliver the contents and formats needed at the presentation layer Resource Management Layer Define the data sources and data organization needed to implement the application logic Information System Information System Define access channels and client platforms Emphasizes final goals of system (both functional and non-functional)

7. Two-tier Architecture Sanjoy Sanyal (Tech for NonGeek) Client Presentation Layer Resource Management Layer Application Layer Server Separates the presentation layer which resides in the client The result is a client server system where the client has the ability to further process the information provided by the server Clients can be thin (limited functionality) or fat (rich functionality) Historically emerged with the PC

10. Three-tier Architecture Sanjoy Sanyal (Tech for NonGeek) Client Presentation Layer Resource Management Layer Application Layer Middleware Historically emerged increase in network bandwidth provided by LANs Solves the problem of integrating between servers Clearly separates each of the three layers The presentation layer resides in the client Introduces middleware: an additional layer between the clients and server that integrates between different information services The resource management layer consists of all servers that are being integrated The servers in the resource management layer can each have their application and resource management layers

12. N-tier Architecture Sanjoy Sanyal (Tech for NonGeek) Client Web browser Resource Management Layer Application Layer Middleware Solves the problem of providing connectivity thru the Internet The Client is a Web browser Web Server is incorporated in the presentation layer The presentation layer is distributed between the Web browser, the Web Server and the code that prepares the HTML pages. Additional modules (e.g. HTML filters) may be necessary to translate between the different data formats used in each layer. Presentation layer Web Server HTML filter

13. Modern N-tier Architecture complexity Sanjoy Sanyal (Tech for NonGeek) Internet Remote Clients Database Server File Server Application Internal Clients LAN Web Server Cluster LAN Middleware application logic LAN Middleware application logic LAN Wrappers and gateways LAN Additional resource management layers LAN Gateway Remote clients access the system over a firewall There are internal clients who also access the services The Web Server and the Application logic layer are often configured as a cluster of machines for higher fault tolerances and throughput The resource management layer can consist of a variety of systems from a database server to additional links to other 2/3/N tier systems