We distinguish the limitations of our work into the ones relating to the functionality of MyPHRMachines as currently implemented and the ones relating to the research method adopted for its evaluation.
About the functionality, myPHRMachines is likely to lead to numerous personal application islands, in which each patient collects heterogenous PHR data and application software. This can lead to a very chaotic repository of health information and related functionality that can be very hard to maintain for the average patient. The issue can be overcome by a careful
design of the interface of MyPHRMachines used by patients to upload, share, and, generally, organize their PHR data, which should be intuitive and hide technical details.
Another limitation previously identified is the lack of Internet access for the VMs. In principle, this prevents a VM to call external (Web) services and, therefore, to combine together such services, e.g. pipelining genomic diagnostics
services available on the Internet. We argue, however, that the same services can be deployed within the trusted domain of MyPHRMachines and be available to all patients to be used. Moreover, we clarified that, for trusted VMs, controlled access to specific Internet addresses can be configured by means of a web proxy. Users should be properly informed of the kind of VM session they are running: a session without Internet access can be trusted blindly while a session with controlled Internet access is only as trustworthy as the Internet sites for which the proxy allows access.
Another consequence of the lack of internet access in enduser VM sessions is that the software inside such VM sessions
cannot automatically update itself. We argue that this is an acceptable limitation, too. First of all, most automated internet
updates are security-related and, therefore, irrelevant for VMs without internet access. Secondly, MyPHRMachines is
designed to allow frequent updates at the level of VM images. End-users are expected to have short-living, stateless, VM
sessions and therefore if VM updates are provided frequently, then end-users benefit from the functional software updates
soon enough.