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Comparing Technologies
This is a very brief, over-simplified discussion of the three technologies
currently employed to access remote data in VHA. We will take them in
chronological order, i.e., the order in which they were developed.
WebTop
It should first be noted that this is the current WebTop design, not the original. Little explanation is required. The user interface is Internet Explorer. It of course communicates with IIS which in turn uses JRun Java servlets to communicate with VistA. The links between "WebTop" and the various VistA sites are direct links, from the web server to each VistA. WebTop is limited to a participating collection of sites, and to participate a site must contribute a generic VistA account. This has a few drawbacks, the two most significant being:
An interesting feature of WebTop is that all communication between the servlets and VistA is accomplished with a single RPC that uses varying sets of parameters.
CPRS Remote Data Views (RDV)
The first thing to notice with RDV is that it communicates only with the local VistA, which in turn communicates with the remote VistAs. Here's how it works:
Or can you?
VistaWeb with MDO
As with WebTop, the VistaWeb user interface is Internet Explorer and the web server is IIS. Instead of JRun servlets however, VistaWeb uses uses Medical Domain Objects (MDO) to communicate with VistA. And, as with WebTop, communication between the web server and the various VistAs is direct. The big difference, though, is MDO is able to use VistA visitor accounts. It can do this because it "knows" how to give a visitor account the CPRS context as a secondary menu option. So it combines the security of visitor accounts with the speed of direct communication and adds the ability to fetch patient data from any VHA site.
One may object that such a visitor account is not so secure once it has a context, but remember, there's still no access or verify code. So if you could log onto such an account you would indeed be authorized to execute CPRS RPCs, but you can't log on. What's more, the user must have CPRS authorization at the local site to begin with since the RPCs MDO uses to set the context in the remote sites cannot be executed otherwise.