Feature Groups

Features can be grouped in order to place a constraint on how the features are used by a certain product [19]. Establishing these relationships among features also support building a modular SPL architecture [20]. According to PLUS method [19, Chapter 5.5], there are four types of feature groups, namely exactly-one-of, zero-or-one-of, at-least-one-of, zero-or-more-of. Table 2 describes feature groups and provides additional information about the relationship among features.

Table 2: Feature groups

Feature Group	Feature Group	Features in Feature	Feature
Name	Category	Group	Category
Complaint Specification	at-least-one-of	Animal Complaint	optional
		Food Complaint	mandatory
		Drug Complaint	optional
		Special Complaint	optional
Database	exactly-one-of	MySQL	alternative
		Oracle	alternative
Support services for	at-least-one-of	Query information	alternative
users		RSS feeds	alternative