In software development, a feature model is a compact representation of all the products of the Software Product Line (SPL) in terms of "features". Feature models are visually represented by means of feature diagrams. Feature models are widely used during the whole product line development process and are commonly used as input to produce other assets such as documents, architecture definition, or pieces of code.

A SPL is a family of related programs. When the units of program construction are features—increments in program functionality or development—every program in an SPL is identified by a unique and legal combination of features, and vice versa.

Feature models were first introduced in the Feature-Oriented Domain Analysis (FODA) method by Kang in 1990.^[1] Since then, feature modeling has been widely adopted by the software product line community and a number of extensions have been proposed.

Background

A "feature" is defined as a "prominent or distinctive user-visible aspect, quality, or characteristic of a software system or system".^[1] The focus of SPL development is on the systematic and efficient creation of similar programs. FODA is an analysis devoted to identification of features in a domain to be covered by a particular SPL.^[1]

Feature modeling notations

Current feature modeling notations may be divided into three main groups, namely:

• Basic feature models
• Cardinality-based feature models
• Extended feature models

A feature diagram representing a configurable e-shop system.

Semantics

The semantics of a feature model is the set of feature configurations that the feature model permits. The most common approach is to use mathematical logic to capture the semantics of a feature diagram.^[5] Each feature corresponds to a boolean variable and the semantics is captured as a propositional formula. The satisfying valuations of this formula correspond to the feature configurations permitted by the feature diagram. For instance, if ${\displaystyle f_{1}}$ is a mandatory sub-feature of ${\displaystyle f_{2}}$, the formula will contain the constraint ${\displaystyle f_{1}\Leftrightarrow f_{2}}$.^[6]

The following table provides a translation of the basic primitives. We assume that the diagram is a rooted tree with root ${\displaystyle r}$. The semantics of a whole diagram is a conjunct of the translations of the elements contained in the diagram. Therefore, in case all elements are written in Conjunctive normal form (CNF), then the terms can easily be combined with logical AND and the whole logical expression will remain in CNF.

Feature Diagram Primitive	Semantics	Semantics in Conjunctive normal form
${\displaystyle r}$ is the root feature	${\displaystyle r}$	${\displaystyle r}$
${\displaystyle f_{1}}$ mandatory sub-feature of ${\displaystyle f}$	${\displaystyle f_{1}\Leftrightarrow f}$	${\displaystyle (f_{1}\lor \lnot f)\land (\lnot f_{1}\lor f)}$
${\displaystyle f_{1}}$ optional sub-feature of ${\displaystyle f}$	${\displaystyle f_{1}\Rightarrow f}$	${\displaystyle (\lnot f_{1}\lor f)}$
${\displaystyle f_{1},\dots ,f_{n}}$ or sub-features of ${\displaystyle f}$	${\displaystyle f_{1}\lor \dots \lor f_{n}\Leftrightarrow f}$	${\displaystyle (f_{1}\lor \dots \lor f_{n}\lor \lnot f)\land \bigwedge _{i=1\dots n}(f_{i}\lor \lnot f)}$
${\displaystyle f_{1},\dots ,f_{n}}$ alternative (xor) sub-features of ${\displaystyle f}$	${\displaystyle \left(f_{1}\lor \dots \lor f_{n}\Leftrightarrow f\right)\land \bigwedge _{i<j}\lnot (f_{i}\land f_{j})}$	${\displaystyle (f_{1}\lor \dots \lor f_{n}\lor \lnot f)\land \bigwedge _{i=1\dots n}(f_{i}\lor \lnot f)\land \bigwedge _{i<j}(\lnot f_{i}\lor \lnot f_{j})}$
${\displaystyle f_{1}}$ requires ${\displaystyle f_{2}}$	${\displaystyle f_{1}\Rightarrow f_{2}}$	${\displaystyle (\lnot f_{1}\lor f_{2})}$
${\displaystyle f_{1}}$ excludes ${\displaystyle f_{2}}$	${\displaystyle \lnot (f_{1}\land f_{2})}$	${\displaystyle (\lnot f_{1}\lor \lnot f_{2})}$

Configuring products

A product of the SPL is declaratively specified by selecting or deselecting features according to user's preferences. Such decisions must respect the constraints imposed by the feature model. A "configurator" is a tool that assists the user during a configuration process. For instance by automatically selecting or deselecting features that must or must not, respectively, be selected for the configuration to be completed successfully. Current approaches use unit propagation^[7] and CSP solvers.^[4]

Properties and analyses

An analysis of a feature model targets certain properties of the model which are important for marketing strategies or technical decisions. A number of analyses are identified in the literature.^[8][9] Typical analyses determine whether a feature model is void (represents no products), whether it contains dead features (features that cannot be part of any product), or the number of products of the software product line represented by the model. Other analyses focus on comparing several feature models (e.g. to check whether a model is a specialization or refactoring or generalization of another).^[10]

See also

• Domain analysis
• Domain engineering
• Feature-oriented Programming - a paradigm for software product line synthesis
• Product Family Engineering
• Software Product Lines

References

External links

• Feature Model Repository Wiki
• Software Product Line Engineering with Feature Models