Dec 16 2011

Conversation with Ralph Johnson about Big Ball of Mud Systems

Published by at 4:35 pm under Conversations with Tom,Videos

This is a video transcript of a Skype conversation I had this morning with Ralph Johnson this morning about refactoring VistA. I think that there are some fascinating ideas here about thinking about refactoring in layers, rather than a single lump, as well as the notion of creating a “semantic overlay” layer that would open VistA up to the rest of the Linked Data world (with appropriate security, as already expressed in VistA). Ralph is one of the gurus of object orientated software, agile development, and refactoring. I had a video chat with Ralph Johnson, software refactoring and object-oriented patterns guru, regarding ways of looking at refactoring VistA. He talks about “Big Ball of Mud” systems , and ways of managing them, particularly through Shearing Layers… which were the topic of Stewart Brand’s “How Buildings Learn” book. I talked about VistA patterns of “Creating a Path of Least Resistance” – with the example that the 1978 VistA design meeting created a common date management routine that was Y2K compatible, making it easier to by compatible. I also spoke about the notion of creating a “Shearing Layer” above VistA – a semantic overlay connecting the existing VistA system data dictionary to the outside world, allowing VistA to participate in the Linked Data world, RDF Semantic mashups. This would also have the advantage of extending the current VistA privacy semantics out to the network interface. I also talked about the scale of VIstA being a critical factor that is often overlooked – “bigger is different” and this has both its drawbacks and its advantages.


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