Implementation:
1. View class: view for some process; ViewTest class
2. View class: constructor is used to perform topological sorting to give a witness for PRAM Consistency. It is remained to be tested.

Refactor:
1. remove public static field "WRITEPOOL" from ReadIncObservation and ClosureObservation; extract them into super class BasicObservation
2. ReadIncOperation: extract "predecessors" and "successors" into super class BasicOperation; dynamic update to them when different order rules are applied