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module RD
# DocumentStructure defines and restricts structure of document tree.
# it consists of ElementRelationship
class DocumentStructure
def initialize
@relationships = []
end
def add_relationships(*relations)
@relationships += relations
end
def define_relationship(parent, child)
add_relationships(ElementRelationship.new(parent, child))
end
def each_relationship
@relationships.each do |i|
yield(i)
end
end
def is_valid?(parent, child)
each_relationship do |i|
return true if i.match?(parent, child)
end
false
end
end
# ElementRelationship is knowledge about parent-children relationship
# between Elements.
class ElementRelationship
attr_reader(:parent, :child)
def initialize(parent, child)
@parent = parent
@child = child
end
def match?(parent, child)
parent.is_a? @parent and child.is_a? @child
end
end
end
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