Clean Architecture

Craft Dispatch System
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phone line turned into a transition in that finite state machine. The existing 
process would start a new process dictated by the state machine to handle 
that event; then the existing process would either exit or wait on a queue.
This externalized state machine allowed us to change the flow of the 
application without changing any code (the Open-Closed Principle). We 
could easily add a new service, independently of any of the others, and wire 
it into the flow by modifying the text file that contained the state machine. 
We could even do this while the system was running. In other words we had 
hot-swapping
and an effective BPEL (Business Process Execution Language).
The old ER approach of using disk files to communicate between services was 
too slow for this much more rapid flip-flopping of services, so we invented a 
shared memory mechanism that we called the 3DBB.
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The 3DBB allowed 
data to be accessed by name; the names we used were names assigned to each 
state machine instance.
The 3DBB was great for storing strings and constants, but couldn’t be used 
for holding complex data structures. The reason for this is technical but easy 
to understand. Each process in MP/M lived in its own memory partition. 
Pointers to data in one memory partition had no meaning in another memory 
partition. As a consequence, the data in the 3DBB could not contain pointers. 
Strings were fine, but trees, linked lists, or any data structure with pointers 
would not work.
The trouble tickets in the trouble ticket system came from many different 
sources. Some were automated, and some were manual. The manual entries 
were created by operators who were talking to customers about their troubles. 
As the customers described their problems, the operators would type in their 
complaints and observations in a structured text stream. It looked something 
like this:
/pno 8475551212 /noise /dropped-calls
12. Three-Dimensional Black Board. If you were born in the 1950s, you likely get this reference: Drizzle, 
Drazzle, Druzzle, Drone.
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