9.351 Systems Analysis & DesignDistributed Systems & User Interface1 Distributed Systems Distributed system = IS that contains a network component and distributes 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 LANWAN

9.351 Systems Analysis & DesignDistributed Systems & User Interface2 Client = A network member issuing requests for IS services. Server = A network member responding to requests for IS services. Distributed Systems LAN-Based Architectures ClientServer Request for Service Service

9.351 Systems Analysis & DesignDistributed Systems & User Interface3 Client-Server Designs (Architectures): depend on sharing or not services between client and server. ClientServer Functionality Information User Interface Control Any can be performed by client or server individually or in 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 & DesignDistributed Systems & User Interface4 WAN-Based Architectures: Web SystemsDistributed Systems ClientApplication Server 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 & DesignDistributed Systems & User Interface5 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 & DesignDistributed Systems & User Interface6 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 SystemsWAN-Based Architectures: Web Systems