9.351 Systems Analysis & Design

Distributed Systems & User Interface 1

Distributed Systems

Distributed system = IS that contains a network component anddistributes system services among network members.

Distributed Systems (Architectures)

•Network members: Client, Server, Output Devices (e.g., printers)

•System services (what an IS is; the third view in 9.351): • Functionality (Processing, “Analysis”)• Information (Data Management, Storage in narrow sense)• User Interface (Presentation)

General Principles

LAN WAN

9.351 Systems Analysis & Design

Distributed Systems & User Interface 2

• Client = A network member issuing requests for IS services.

• Server = A network member responding to requests for IS services.

Distributed Systems LAN-Based Architectures

Client Server

Request for Service

Service

9.351 Systems Analysis & Design

Distributed Systems & User Interface 3

• Client-Server Designs (Architectures): depend on sharing or not services between client and server.

Client Server

• Functionality

• Information

• User Interface

Control

Any can be performed by client or server individually orin a sharing mode (e.g., client manages user interface,server information and functionality (processing) is shared.

Distributed Systems LAN-Based Architectures

9.351 Systems Analysis & Design

Distributed Systems & User Interface 4

WAN-Based Architectures: Web SystemsDistributed Systems

Client ApplicationServer

Request for Service

Service

• General principles apply

• Three-Tier Architecture with Application Server

Server Local Request in Native Format

Response in Native Format

9.351 Systems Analysis & Design

Distributed Systems & User Interface 5

• Software Component Architecture (COM/DCOM/ActiveX vs. CORBA) Web Services (e.g., .NET )

• HTTL vs. XML (Display vs. Content)

• XML (Extensible Markup Language)• rising data exchange standard for distributed applications

• focused on information content, while user interface handled by style sheet languages like XSL (Extensible Style Language) & CSS (Cascading Style Sheets)

WAN-Based Architectures: Web SystemsDistributed Systems

9.351 Systems Analysis & Design

Distributed Systems & User Interface 6

• SOAP (Simple Object Access Protocol)

• defines messages implemented in XML

• transport protocols could be any (SMTP, HTTP most

frequently used)

• XML and SOAP are basis to Web services that scale up

distributed system architectures (e.g., .NET)

Distributed Systems WAN-Based Architectures: Web Systems