Client-server architectures

Transcription

1 Client-server architectures

2 Client/Server approach Basic concept 1. Clients are requesting information (e.g., a specific web page) 2. Servers are responding to individual requests Response Client Server Request Dept. of Geo Information Processing

3 Client/Server approach Depending on the location where the actual information processing takes place, two kinds of task distribution strategies can be distinguished: 1. Thin Clients: most of the processing is done on the server side 2. Thick (or Fat) Clients: most of the processing is done on the client side Example: Imagine a server/client application, that offers the user the functionality to request a rectified satellite image. How can this organized in a client/server environment? Dept. of Geo Information Processing

4 Thin client 1. Client offers just a user interface to formulate the request (e.g. to select the image to be rectified) 2. The request is sent to the server Storage Server 3. Requested data is retrieved from a storage device (here: an non-rectified image) 4. The retrieved data is processed (here: rectified) 5. Processed data is sent back to the client Input/output Processing Dept. of Geo Information Processing

5 Typical thin-client solution Server Client Storage Input/output Spatial query Spatial query input/output input/output Processing DBMS DBMS Spatial Spatial transformations transformations & & Analysis Analysis Spatial Spatial data data Attribute Attribute data data Dept. of Geo Information Processing

6 Thick client Client provides processing capabilities itself (e.g. rectification would be performed on the client machine) Different from thin clients a fat client has to be equipped with more sophisticated software Input/output Processing Storage Server Dept. of Geo Information Processing

7 Thin clients Pros No complex software has to be installed. If the application is web-based A client-side browser will be sufficient in most cases The system is applicable from every web-terminal Cross-platform interoperability Performance more or less independent from the client hardware ( easy migration to mobile devices) Instant updates and revision (mainly the server-side parts of the software have to be updated) Dept. of Geo Information Processing

8 Thin clients Cons Usability heavily relies on the network connection Availability (no offline-work) Speed Typically a low level of interactivity Interaction means heavy network traffic that has to be avoided (server access for each single action) Therefore, thin clients typically offer a coarse grained functionality (processing by big chunks) Often limited access to resources on the user machine (disk, printer, etc.) Dept. of Geo Information Processing

9 Thick clients Pros Typically a higher degree of functionality and interactivity Able to make use of local resources (e.g. local data) Appear to be faster, because some of the processing tasks are performed on the client machine (it turns into a con, if the hardware is not sufficient) Basically able to work temporary offline Dept. of Geo Information Processing

10 Thick clients Cons Performance depends on the client-side hardware Complex software applications have to be installed Typically higher hardware requirements Higher maintenance expenses (time & money) No ad-hoc access from more or less arbitrary locations, as in case of a web-based thin-client solution Dept. of Geo Information Processing

11 Thin vs. thick clients conclusion Both solutions have their pros and cons. Therefore the decision of a thin-client or thickclient solution is not easy to make and depends heavily upon the user requirements the solution has to meet Dept. of Geo Information Processing