Development of a flash-based filestore

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Nowadays, many formal methods are used in the area of software development accompanied by a number of advanced theories and tools. However, more experiments are still required in order to provide significant evidence that will convince and encourage users to use, and gain more benefits from, those theories and tools. Event-B is a formalism used for specifying and reasoning about systems. Rodin is an open and extensible toolset for Event-B specification, refinement and proof. The flash file system is a complex system that is challenging to specify and verify at this moment in time. This system was chosen as a case study for our experiments, carried out using Event-B and the Rodin tool. The experiments were aimed at developing a rigorous model of flash-based file system, and providing useful evidence and guidelines to developers and the software industry. We believe that these would convince users and make formal methods more accessible.


An Incremental Refinement Approach to a Development of a Flash-Based File System in Event-B

The work on the development of a flash-based file system in Event-B is reported in a PhD thesis by Kriangsak Damchoom[1].

Other papers and Rodin achives are available below.

Modelling and proof of a Tree-structured File System

By Damchoom, Kriangsak and Butler, Michael and Abrial, Jean-Raymond.[2]

We present a verified model of a tree-structured file system which was carried out using Event-B and the Rodin platform. The model is focused on basic functionalities affecting the tree structure including create, copy, delete and move. This work is aimed at constructing a clear and accurate model with all proof obligations discharged. While constructing the model of a file system, we begin with an abstract model of a file system and subsequently refine it by adding more details through refinement steps. We have found that careful formulation of invariants and useful theorems that can be reused for discharging similar proof obligations make models simpler and easier to prove.

Applying Event and Machine Decomposition to a Flash-Based Filestore]

By Damchoom, Kriangsak and Butler, Michael.[3]

An Incremental Refinement Approach to a Development of a Flash File System archive

By Damchoom, Kriangsak and Butler, Michael.

An incremental refinement was chosen as a strategy in our development. The refinement was used for two different purposes: feature augmentation and structural refinement (covering event and machine decomposition). Several techniques and styles of modelling were investigated and compared; to produce some useful guidelines for modelling, refinement and proof. The model of the flash-based file system we have completed covers three main issues: fault-tolerance, concurrency and wear-levelling process. Our model can deal with concurrent read/write operations and other processes such as block relocation and block erasure. The model tolerates faults that may occur during reading/writing of files. We believe our development acts as an exemplar that other developers can learn from.

Multi-Levelled Refinement and Evolution of a Flash File System Model in Event-B and Rodin archive

By Damchoom, Kriangsak and Butler, Michael.

This work is an extension of the work presented above. The focus of this work is to outline an evolution of the model when the requirements change. Evolution of the models is necessary when the requirements change. The point is how to deal with this. How much changes that impact the models? How reusability can be achieved? and how flexibility of the language and tool are?

References