Java Reference
In-Depth Information
The user can load the description of a cartographic map from a previously
generated XML file.
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Figure 15.5 shows three views of a cartographic map. The first view
shows only the sites of the map, the second view only the links, and the last
view only the areas.
15.5
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Prototype 2: The data linker
This section analyses the requirements of the data browsing functionality
needed to build the GIS data model. The second prototype implements the
data linker as a standalone application that allows the user to select graphical
features in the cartographic map and associate information stored in a
relational database.
15.5.1
Analysis
The power of a GIS is its versatility. As we have seen in the previous section,
we can build a cartographic map by simply selecting a picture of a geo-
graphic area (e.g. an aerial photograph) and overlapping geometric features
that represent active portions of that picture. The last step consists of
associating each geometric feature with thematic information (e.g. historical
events) retrieved from persistent storage. In this case, versatility means that
the GIS does not impose strong constraints on the origin of the data (where
they are stored) and their format. For the sake of simplicity, we make a few
assumptions.
Data origin
. We assume that thematic information is stored in relational
databases. This is the most general and common type of persistent storage
and the most efficient for large amounts of data. Geographic features
belonging to the same cartographic map may be associated with infor-
mation stored in a multitude of databases.
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Data format
. Typically, thematic information assumes the form of textual
description (e.g. a bibliographic reference) or simple data, such as strings
(e.g. the name of a Consular route), integers (the population of Rome), or
dates (e.g. the murder of Julius Caesar).
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We can suppose that the GIS manager is able to generate query tables, i.e.
new tables that record a synthesis of a table or a set of tables in a database.
Let's consider the GIS service described in Section 15.2.1. The Historic
Archive of Rome manages two databases: “Historic Geography” and
“Ancient People”. The former stores information related to the historical
evolution of human settlements in Italy and has three main query tables:
Cities
,
Routes
and
Ports
. The latter records information related to the people
that were native to the Italian peninsula or occupied it in different historical
periods. It has two main query tables:
Native
and
Barbarians
. The attributes
