This
simple node has the label composed by the name Name and the valid time interval
[01/05/05,now]. The node Group is the root of the graph, and is connected to
its property by means of the edge with name GroupName and valid time interval
[01/05/05,now]. The valid time interval [01/05/05,now] represents the fact that the
group of restaurants is valid from June 1, 2005 until now.
Information about restaurants, addresses, and menu are represented respectively by
means of the complex nodes Restaurant, Address, and Menu. Their properties are
represented as simple nodes such as Name, Position, Price, Street, and City.
Data in Figure 1 are semistructured: the same information, such as the address of the
restaurant, is represented in different ways, that is as a simple node for ???Big Home,???
Temporal Semistructured Data Models and Data Warehouses 28
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and as a complex node for ???The Beach.??? The GEM data model allows the representation
of data evolution, such as the increasing of a price. For example, in Figure 1,
the price of the ???Summer??? menu increased from $25 to $30 on June 15, 2005. This
evolution is represented, in a GEM graph managing valid time, by means of a new
simple node with the same name (???Price???), with the new value (???$30???) and valid
time interval starting from ???15/06/05??? and ending ???now.
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