Predefined Entities / Traits in FamixNG

To analyze a system in a given programming language, Moose must have a meta-model for that language. For example, for Java the meta-model defines that Java programs have classes, containing methods, invoking other methods, etc. The meta-model describes the entities that compose a program in the given language and how they are related.

On another page, we explain how to define a meta-model: create new entities, define relationships, properties, etc. On this page, we present the library of predefined entities that is part of FamixNG and helps declaring new entities by offering typical properties / relationships that are needed.

In FamixNG, recurrent properties are modeled into traits. New entities are created as classes composed from these existing traits. Some common entities (like Packages) are also proposed, precomposed with common traits. Here we list all currently available traits.

FamixNG is still under development, and the library of available traits is subject to change. The following should nevertheless help users make sense of the more than one hundred traits available.

Categories of traits

First, one can divide the set of traits into four categories:

• Categories of traits
• Association Traits
• Technical Traits
• Property Traits
• Terminal Traits

They are described as follows:

Association Traits

Association traits model the fact that an entity is used (referred to) in the source code. Such a reference creates an association between the using entity (refers to) and the entity that is used (is referred to). This includes the four associations of the old Famix: Inheritance, Invocation (of a function or a method), Access (to a variable), and Reference (to a type).

Associations should be thought of as n-to-m relationships between entities. For that reason, they are reified into their own traits. Associations define two roles (from and to) to identify both ends of the association. Using an association involves:

• defining a class representing the association (for example, Access, using the trait FamixTAccess)
• defining two classes at each end of the association (for example, Function using the trait FamixTWithAccess, and Variable using the trait FamixTAccessible).

There are five full-fledged associations in FamixNG:

• FamixTAccess, from: FamixTWithAccess, to: FamixTAccessible
  
• FamixTInheritance, from: FamixTWithInheritance, to: FamixTWithInheritance
  
• FamixTInvocation, from: FamixTWithInvocation, to: FamixTInvocable, for OO programs, there is an extra receiver: FamixTInvocationReceiver
  
• FamixTReference, from: FamixTWithReferences, to: FamixTReferenceable
  
• FamixTTraitUsage, from: FamixTWithTrait, to: FamixTTrait
  

To these five we added two more specialized “associations”: DereferencedInvocation (call of a pointer to a function in C) and FileInclude (also in C). These do not reify the association as a separate entity, but they might do so in the future. For now there are only two traits to put at each end of the relationship:

• FamixTDereferencedInvocation and FamixTWithDereferencedInvocations
  
• FamixTFileInclude and FamixTWithFileInclude
  

Technical Traits

Technical traits do not model programming language entities but are used to implement Moose functionalities.

Currently, this includes several types of FamixTSourceAnchors that allow recovering the source code of the entities. A typical FamixTSourceAnchor contains a filename, and start and end positions in this file.

Technical traits may also implement software engineering metric computation (TLCOMMetrics), or ways to model the programming language used (all SourceLanguage), or be used to implement the generic MooseQuery engine.

Property Traits

Property traits model composable properties that source code entities may possess. Some examples are FamixTNamedEntity (entities that have a name), FamixTTypedEntity (entities that are statically typed), or a number of entities modeling ownership: FamixTWithGlobalVariables (entities that can own FamixTGlobalVariables), FamixTWithFunctions (entities that can own FamixTFunctions), …

There are 46 property traits currently in FamixNG including 38 traits modeling ownership of various possible kinds of entities (FamixTWith...).

Terminal Traits

Terminal traits model entities that can be found in the source code such as Functions, Classes, Exceptions, … These entities are often defined as a composition of some of the property traits. For example, FamixTClass is composed of: FamixTInvocationsReceiver (class can be receiver of static messages), FamixTPackageable, FamixTType (classes can be used to type other entities), FamixTWithAttributes, FamixTWithComments, FamixTWithInheritances, FamixTWithMethods.

The name terminal trait refers to the fact that they can be used directly to create a programming language concept (a class, a package), whereas property traits are typically composed with other traits to make a meaningful programming language concept.

There are 38 such terminal traits currently in FamixNG.