code_metrics

The purpose of this tool is to assess qualities of source code that may predict negative aspects such as entity coupling, cohesion, complexity, error-proneness, and overall maintainability. It is meant to be extensible via the addition of objects implementing new metrics.

API documentation

To consult this tool API documentation, open in a web browser the link:

docs/library_index.html#code-metrics

For sample queries, please see the SCRIPT.txt file in the tool directory.

Loading

This tool can be loaded using the query:

| ?- logtalk_load(code_metrics(loader)).

Available metrics

Currently, the following metrics are provided:

  • Number of Clauses (noc_metric)

  • Number of Rules (nor_metric)

  • Unique Predicate Nodes (upn_metric)

  • Cyclomatic Complexity (cc_metric)

  • Depth of Inheritance (dit_metric)

  • Efferent coupling, afferent coupling, instability, and abstractness (coupling_metric)

  • Documentation (doc_metric)

  • Source code size (size_metric)

  • Halstead complexity (halstead_metric)

All metrics require the source code to be analyzed to be loaded with the source_data flag turned on.

A helper object, code_metrics, is also provided allowing running all loaded individual metrics.

For usage examples, see the SCRIPT.txt file in the tool directory.

For code coverage metrics, see the lgtunit tool documentation.

For interpretation of the coupling metric scores, see e.g. the original paper by Robert Martin, “OO Design Quality Metrics”:

@inproceedings{citeulike:1579528,
    author = "Martin, Robert",
    booktitle = "Workshop Pragmatic and Theoretical Directions in Object-Oriented Software Metrics",
    citeulike-article-id = 1579528,
    citeulike-linkout-0 = "http://www.objectmentor.com/resources/articles/oodmetrc.pdf",
    keywords = "diplomarbeit",
    organization = "OOPSLA'94",
    posted-at = "2007-08-21 11:08:44",
    priority = 0,
    title = "OO Design Quality Metrics - An Analysis of Dependencies",
    url = "http://www.objectmentor.com/resources/articles/oodmetrc.pdf",
    year = 1994
}

The Halstead metric computation uses the reflection API for performance. The main consequence of this choice is that we abstract all predicate arguments. A computation closer to the original definition of the metric would require switching to use the parser to collect information on syntactic literals, which would imply a much large computation cost.

The coupling metric was also influenced by the metrics rating system in Microsoft Visual Studio and aims to eventually emulate the functionality of a maintainability index score.

The unique predicate nodes (UPN) metric is described in the following paper:

@article{MOORES199845,
    title = "Applying Complexity Measures to Rule-Based Prolog Programs",
    journal = "Journal of Systems and Software",
    volume = "44",
    number = "1",
    pages = "45 - 52",
    year = "1998",
    issn = "0164-1212",
    doi = "https://doi.org/10.1016/S0164-1212(98)10042-0",
    url = "http://www.sciencedirect.com/science/article/pii/S0164121298100420",
    author = "Trevor T Moores"
}

The cyclomatic complexity metric uses the same predicate abstraction as the UPN metric and it is also described in the above paper besides the original paper by Thomas J. McCabe:

@inproceedings{McCabe:1976:CM:800253.807712,
    author = "McCabe, Thomas J.",
    title = "A Complexity Measure",
    booktitle = "Proceedings of the 2Nd International Conference on Software Engineering",
    series = "ICSE '76",
    year = 1976,
    location = "San Francisco, California, USA",
    pages = "407--",
    url = "http://dl.acm.org/citation.cfm?id=800253.807712",
    acmid = 807712,
    publisher = "IEEE Computer Society Press",
    address = "Los Alamitos, CA, USA",
    keywords = "Basis, Complexity measure, Control flow, Decomposition, Graph theory, Independence, Linear, Modularization, Programming, Reduction, Software, Testing",
}

Defining new metrics

New metrics can be implemented by defining an object that imports the code_metric category and implements its score predicates. There is also a code_metrics_utilities category that defines useful predicates for the definition of metrics.

Third-party tools

cloc is an open-source command-line program that counts blank lines, comment lines, and lines of source code in many programming languages including Logtalk. Available at https://github.com/AlDanial/cloc

ohcount is an open-source command-line program that counts blank lines, comment lines, and lines of source code in many programming languages including Logtalk. Available at https://github.com/blackducksoftware/ohcount

tokei is an open-source command-line program that counts blank lines, comment lines, and lines of source code in many programming languages including Logtalk. Available at https://github.com/Aaronepower/tokei