Notation The root node the diagram is called the concept node All nodes below the concept node represent features and subfeatures Mandatory features are denoted by a simple edge ending with a filled circle Optional features are denoted by a simple edge ending with an open circle Subsets of features may be alternatives denoted by connecting the edges pointing to alternatives with an arc If an arc connecting edge is filled in, it indicates that any subset of the alternatives may be chosen; otherwise the alternatives are mutually exclusive
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