https://github.com/thomwright/rusty-cats
Cohesion/coupling Analysis for TypeScript
https://github.com/thomwright/rusty-cats
Last synced: 2 months ago
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Cohesion/coupling Analysis for TypeScript
- Host: GitHub
- URL: https://github.com/thomwright/rusty-cats
- Owner: ThomWright
- Created: 2020-11-19T19:07:35.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2020-11-22T14:11:04.000Z (over 4 years ago)
- Last Synced: 2025-01-18T17:57:05.536Z (4 months ago)
- Language: Rust
- Size: 102 KB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Rusty CATS
[Another go at this](https://github.com/ThomWright/cats)
## Goal
A quantitative measure of coupling and cohesion between TypeScript modules/files.
As I see things, there are two main structures to consider here:
1. the dependencies between modules/files (a directed graph)
2. the file/directory structure (a tree)
Some things I think are good:
- the dependency graph being acyclic
- the dependency graph being tree-like
- the dependency graph closely mirroring the file/directory structure
- dependencies being close together (in terms of how far you need to traverse the directory tree to resolve a dependency)
I am not sure how best to quantify any of these measures.
## An information theory approach
This approach is [described here](http://www.sdml.cs.kent.edu/library/Allen99.pdf).
Pros:
- gives quantitative measures for:
- intermodule coupling
- intramodule coupling
- cohesion
Cons:
- I'm not familiar enough with the maths to quickly understand or apply it
- assumes all modules are equal, does not consider submodules
- e.g. if a file is a node, and a directory is a grouping of nodes (a module), how do we handle subdirectories?
### Definitions
- _MS_ - Modular system, represented as a graph
- _S_ - a subgraph with n+1 nodes, including 1 for the environment (disconnected)
- _ns_ - number of distinct labels (each node is labelled with the set of connected edges)
- _pl_ - proportions of distinct labels
- _pL(i)_ - proportion of a node _i_'s distinct label set (relative to total number of nodes)
- [_Entropy_](https://en.wikipedia.org/wiki/Entropy_(information_theory)) - average information per node
- _Minimum description length_ - the total
amount of information in the structure of the graph
- _I(S)_ - minimum description length
- _Intermodule coupling_ - minimum description length of the relationships in _S_ where _S_ is a subgraph with intermodule edges only
- _Intramodule coupling_ - minimum description length of the relationships in _S'_ where _S'_ is a subgraph with intramodule edges only
- _Cohesion_ - intramodule coupling / maximum intramodule coupling (all nodes connected)
### Equations
#### Entropy of the distribution of node labels
_H(S) = Σ(-pl log pl)_
from _l=1_ to _ns_
_H(S) = Σ((-log pL(i))/(n + 1))_
from _i=0_ to _n_
#### Minimum description length
_I(S) = (n + 1) H(S)_
_I(S) = Σ(-log pL(i))_
from _i=0_ to _n_
### Example
All diagrams from [1].
#### Intermodule coupling
This is an example of intermodule coupling. All intramodule edges have been removed.
Node 3 has _pL(i)_ of 0.467 because there are 7 nodes with the same distinct label set, and 15 nodes total: 7/15 = 0.467.
| Node | 1 | 2 | 3 | 4 | 7 | 11 | pL(i) |
|------|---|---|---|---|---|----|------------------|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0.067 |
| 2 | 1 | 0 | 0 | 1 | 0 | 0 | 0.067 |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 4 | 0 | 0 | 0 | 0 | 1 | 0 | 0.067 |
| 5 | 0 | 1 | 0 | 0 | 1 | 0 | 0.067 |
| 6 | 0 | 0 | 1 | 0 | 0 | 0 | 0.067 |
| 7 | 0 | 0 | 0 | 0 | 0 | 1 | 0.133 |
| 8 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 9 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 10 | 0 | 0 | 0 | 0 | 0 | 1 | 0.133 |
| 11 | 0 | 0 | 0 | 1 | 0 | 0 | 0.067 |
| 12 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 13 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
| 14 | 0 | 0 | 0 | 0 | 0 | 0 | 0.467 |
Using the equation for entropy:
_H(S) = 7\*0.0732 + 6\*0.26 + 2\*0.194 = 2.46 bits per node_
And minimum description length:
_I(S) = 15 * 2.46 = 36.9 bits_
## Reference material
- [1] [Measuring Coupling and Cohesion: An Information-Theory Approach](http://www.sdml.cs.kent.edu/library/Allen99.pdf)
- [2] [Experiments with Coupling and Cohesion Metrics in a Large System](http://www.csi.uottawa.ca/~tcl/papers/metrics/ExpWithCouplingCohesion.pdf)
- [3] [Quantitative models of cohesion and coupling in software](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.94.183&rep=rep1&type=pdf)