.. index:: coupling_metric
.. _coupling_metric/0:

**object**

``coupling_metric``
===================

Computes entity efferent coupling, afferent coupling, and instability.

| **Author:** Ebrahim Azarisooreh and Paulo Moura
| **Version:** 0.12
| **Date:** 2018/7/17

| **Compilation flags:**
|    ``static, context_switching_calls``


| **Imports:**
|    ``public`` :ref:`code_metrics_utilities <code_metrics_utilities/0>`
|    ``public`` :ref:`code_metric <code_metric/0>`

Public interface
----------------

(see related entities)

Protected interface
-------------------

(see related entities)

Private predicates
------------------

(see related entities)

Operators
---------

(none)

Remarks
-------

* **Efferent coupling (Ce)**: Number of entities that an entity depends on.

* **Afferent coupling (Ca)**: Number of entities that depend on an entity.

* **Instability (I)**: Computed as Ce / (Ce + Ca). Measures the entity resilience to change. Ranging from 0 to 1, with 0 indicating a maximally stable entity and 1 indicating a maximally unstable entity. Ideally, an entity is either maximally stable or maximally unstable.

* **Abstractness (A)**: Computed as the ratio between the number of static predicates with scope directives without a local definition and the number of static predicates with scope directives. Measures the rigidity of an entity. Ranging from 0 to 1, with 0 indicating a fully concrete entity and 1 indicating a fully abstract entity.

* **Entity score**: Represented as the compound term ce_ca_i_a(Ce,Ca,I,A).

* **Dependencies count**: Includes direct entity relations plus calls or dynamic updates to predicates in external objects or categories.

