VISTA Enterprise Network - Successful Implementation, World Class Support

Wednesday, July 22, 2009

Point 6: VISTA's Software Stream Has Many Tributaries, part one

Dear Reader,

In the classic VISTA lifecycle, each VISTA development team relies on user feedback in the National Online Information Sharing package (NOIS) on Forum to figure out its top priorities, but the changes are not made on Forum nor on any central code repository, as discussed in point two. Instead, each package-development team develops its changes in its own package-specific code repository. Developers do not need permission to make changes to their software; they are the tyrannical owners of that software, and they continue to be just so long as they keep their users happy.

Once the developers have solved a problem, they bundle it up using the Kernel package's Kernel Installation and Distribution System (KIDS) and e-mail it to Forum. Using another special Forum package called the Patch Module, they convert the KIDS distribution into a patch and distribute it for testing, verification, and eventually release. The Patch Module maintains a list of subscribers for each VISTA package, so when a patch is released it is automatically e-mailed to all of its subscribers. The power of this e-mail-based push mechanism is something we do not have time to get into in this posting, except to say this is what makes the pending auto-patch system work.

Conceptually, this means the software stream does not flow to a single mouth, a single repository where people have to go to find upgrades. Rather, after Forum the software stream splits into a delta that delivers a stream of software to each subscriber.

This explanation should make clear that the patch stream, the nonstop sequence of incremental improvements to VISTA, also does not begin with a single source, but with many sources, maybe between fifty and a hundred. Forum's role on this outbound half of the lifecycle is strictly that of a traffic cop who sequences the traffic, not that of traditional software manager who controls what gets done and whether it can be released. Forum's role here is to act as the point where the tributaries come together to form a single stream.

Although from the VISTA adopters' perspective Forum produces the steady stream of small advances they can trust to continuously upgrade their systems, from the developers' perspective it is still very easy to separate out, think about, and manage just the thread of development that represents their chosen package. This is how the unmanageable scale of VISTA development is broken down into incremental steps organized into manageable packages and corresponding patch streams.

Concluded in part two tomorrow. . . .

Yours truly,

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