GI321 Client and Server of Distributed GIS Apps - Lecture III.pdf

DEPARTMENT OF SURVEYING & LAND STUDIES GI321 WEB GIS/CARTOGRAPHY Client / Server of Distributed GIS Applications Lecture III GI321 - Web GIS/Cartography (Semester 2) Lecture III Overview Objectives At the com...

DEPARTMENT OF SURVEYING & LAND STUDIES GI321 WEB GIS/CARTOGRAPHY Client / Server of Distributed GIS Applications Lecture III GI321 - Web GIS/Cartography (Semester 2) Lecture III Overview Objectives At the completion of this module, you should be able to;  Conceptualise distributed information systems and client/server computing  Picture the evolution of distributed GIS  Understand the use of client/server architecture at various network communications Reference and Selected Readings  Reference  Peng, Zhong-Ren & Tsou, MH, Internet GIS – distributed Geographic Information Services for the Internet and wireless networks, John Wiley & Sons  Selected Readings  ‘Introduction to client/server networking’,.  Internet Resources  Wikepedia – ‘distributed computing’,  ‘What is distributed computing?’,  Wikepedia – ‘client-server’,  Distributed GIS project,  WHAT IS THE DIFFERENCE BETWEEN THE INTERNET AND THE WWW (WEB)?  -Defined -  The Internet is a network of networks. It is composed of multiple, geographically dispersed networks connected through communication devices and a common set of communication protocols (Peng & Tsou 2003).  The WWW (or simply Web) is an application involving collection of on-line documents written in Hypertext Mark-up Language (HTML) and stored on Web Servers around the world. Web documents are files containing text, graphics, sound, video, and links that are hyper linked and interactive. Hyperlink refers to a link in a document to information within that document or another document. Review  What is distributed systems in the context of GIS?  System distributed across a computer network to integrate, disseminate and communicate geographic information.  E.g. Internet (WebGIS), Wireless environment (Mobile GIS)  Collection of networks and client/server network architecture in which the client is separate from the server.  Information technology advancement such as the internet and the WWW has propelled the development of Distributed GIS. Distributed Computing Systems  Decentralised computing system – networks of computers working coherently to accomplish a common task/objective.  It acts as a single centralised system, with the main difference being a wide geographic dispersion of resources.  Connect users and resources in a user friendly, open and scalable way.  Intro Into Client /Server elements of Distributed GIS Applications  Most GIS applications adopt Client/Server architecture  A Client/ Server application contains three main elements:  1. Presentation  2. Logic  3. Data  These elements are interrelated in Client/ Server architecture.  Intro Into Client /Server elements of Distributed GIS Applications  Presentation relates to the Graphic User Interface (GUI) of GIS programs that allow input from keyboard and mouse.  Logic (or business logic) refers to processing such as query and spatial overlay.  Data is basically needed by the logic to perform processing  Intro Into Client /Server elements of Distributed GIS Applications  Presentation Logic Data element  Main frame applications – the three elements reside on the same machine  Desktop applications – the three elements reside in different machines that are connected via LAN.  Web & Internet applications – the three elements reside in different machines that a connected via a network of computers. Evolutions of GIS. (Source:.) Typical Web GIS Architecture  Uses three tier client/server architecture.  The geoprocessing is broken down into client side and server side tasks. Source: Symposium on Geospatial Theory, processing and application, Ottawa 2002. Server-Side Applications (Thin Client Architecture)  Client uses user interfaces to communicate with server to display results.  All processing is done on the server end. Source: Symposium on Geospatial Theory, processing and application, Ottawa 2002. Advantages of Thin Client Architecture  Central control  Easy for data eminence/ updating  Keep the latest version  Generally cheaper  Integration possibilities  Regarding some cartographic aspects e.g. Font type. Disadvantages of Thin Client Architecture  Not responsive to local needs – users have different invokes  No local accountability – accountability need application on client side.  Large data volume – size of the data base.  Response time slow – browsers take to long to download HTML frame.  Less interactive – limited application and browser abilities in client side.  Vector data does not appear in client side – need additional plug-ins to read vector data. Client-Side Applications (Thick Client Architecture)  Client allows users to perform some data manipulation and analysis locally on their own machines. Source: Byong – Lyol, 1998. Advantages of Thick Client Architecture  Applications take advantage of the processing power of the user’s own computer.  The user can be given greater control of the data analysis process  Once server delivers its response, users can work with the data without having to send and receive messages across the internet. Disadvantages of Thick Client Architecture  The response from the server may involve transferring huge amounts of data, including applets, creating delays.  Large & complex datasets may be hard to process on the client it is not very powerful.  Complex GIS analytical routines may run more slowly on the client if it is not very powerful.  Users may not have the training needed to employ the data and analysis functions properly. Client / Server Computing Source: Tony Kirvan 1997 adapted in.) Traditional Client / Server Model  Desk top GIS running on a LAN – traditional client/server system.  The client and the server is fixed.  Front-end user interface is usually the GUI provided by an appropriate GIS software. Web based Client/Server Architecture  Web browser is used as the front-end user interface.  Uses logical client/server model, meaning the roles of the client & server are not fixed.  Main advantage – resources and data can be accessed from anywhere at any time.  No GIS requirement – web browser acts as a front-end user.  The system can be a ‘Thin’ or ‘Thick’ client.  More scalable & secured compared to traditional client/server model. Distributed component frameworks  Client/server applications based on the Internet but not the Web.  Break up the client and server sides of an application into components that can interoperate across operating systems, networks, languages, applications, tools, and hardware.  Distributed components can prioritise and handle rich and complex requests.  Appropriate for open and distributed GIS environments since they can provide efficient and flexible client/server applications. Guiding Questions? 1. What are the key differences between client/server and distributed architectures in GIS applications? This question explores the fundamental distinctions between the two architectures, including how data is processed, stored, and accessed in each system. 2. How does data synchronization and consistency get maintained in distributed GIS applications? This question addresses the challenges and solutions related to ensuring that data remains consistent and up-to-date across multiple servers and clients in a distributed system. 3. What are the benefits and drawbacks of using a client/server architecture for GIS applications compared to a distributed architecture? This question prompts an examination of the advantages and disadvantages of each architecture, focusing on aspects such as performance, scalability, reliability, and ease of maintenance. 4. How do client/server and distributed GIS architectures handle data security and privacy? This question looks into the security measures and practices employed in both architectures to protect sensitive geographic data and ensure user privacy. 5. What considerations should be taken into account when choosing between a client/server and a distributed architecture for a specific GIS application? This question addresses the factors that influence the decision-making process, including the specific requirements of the GIS application, such as data volume, user load, geographical distribution, and real- time processing needs. END of LECTURE III ANY QUESTIONS? GI321 - Web GIS/Cartography (Semester 2,2022)