20
Carlo Combi, Sara Migliorini, Barbara Oliboni, and Alberto Belussi
Highway
Name
Length
n. Lane
Segments
To
SubSegments
From
To
Toll station
Maintenance
Works
Accident
Point
Gravity
Tail
From
To
Closed
Tail
Where
Traffic
Telepass
Via Card
Operator
From
To
Map
From
Exit
Maintenance
Way-Accident
Schema
Italy-Highway
Polygon
SRS
Line
Line
Point
Owner
Name
Highway-Owner
Fig. 2.1. A portion of the GeoMTGM database schema
is a complex node, while Highway, Segment, SubSegment, Maintenance Work, Toll
Station, and Accident are geographical complex nodes.
Each entity has some textual attributes that are represented by atomic nodes
(depicted as ovals). In Fig. 2.1, Name, Length, n.Lane, and Gravity are examples
of atomic nodes. Moreover, entities can have some multimedia attributes that are
represented through a special kind of atomic node, named stream node. Stream nodes
contain multimedia information as unstructured texts, movies, and sounds; they are
depicted as thick ovals in database instances. In Fig. 2.1, the nodes Traffic and Map
are examples of stream nodes that refer to the files that encode the movie of the
current traffic on the specified toll station and the image of the Highway map, respectively.