Distributed Computing with the Browser

Recently, Subbu posted an interesting discussion of an xml analysis and presentation application – you can read it here: Distributed Computing with the Browser.

This design scenario is a good illustration of the limitations of our current situation with programming . Our current situation is that while the WWW allows a programmer to ignore the network path to an information resource, as programmers, we can’t ignore where computing will be done. The programmer’s choice of technology (framework, language etc etc) carries with it the implicit choice about the location of computation (server or client).

An assumption behind Subbu’s post is that we need to decide the location of processing during the design phase. The purpose of this post is explore how the application could be built using Request Based Distributed Computing RBDC (see backgrounder). With the application recast as a RBDC application, the location-of-processing decisions can be made at runtime based on the availability of computing power and storage, intellectual property, and security issues.

The XML analysis and presentation application using RBDC

(This description presumes that you have read the RBDC backgrounder.)

The key distributed process in this application is the initial analysis of the source XML text, and the saving of the key features into a central database. Lets call this “analyse-save”. With RBDC, the code that performs analyse-save may be written as mobile code that will run on either the server, a proxy or on the client. Analyse-save may be implemented as the code that responds to a http POST request that uploads the source file to the server. It analyses the uploaded file then POSTS the results of the analysis to a central database.

When a RBDC compliant server receives the analyse-save request it may perform the analysis itself on the server or otherwise return the analyse-save code to the client. If the client receives code as a response to its analyse-post request then it would execute the code locally. In either case, the results of the analysis are POSTed to the central database using http.

Clients that have local processing capabilities signal through a http header in the POST request that they are able to accept mobile code as a response to the request. Alternatively clients without processing ability can make the same request signalling that they need the server to do all possible processing.

In this way – the architecture of the solution is the same for Subbu’s cases 1 and 3 with the decision about location of processing being made at runtime, not as part of the design.

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