Geographic information system - Software Development Case Studies in Java - page 412

Decision point

How does the data linker access the contents of the GIS database?

Class DBConnector (see Figure 15.10) plays the role of database proxy. It
implements a persistent layer that loads into memory the contents of the
GIS database and provides the data linker with access to the contents of
the thematic databases. It makes use of three ancillary classes. Class
DBListRecord stores the values of a record extracted from tables Databases ,
i.e. the description of a thematic database (e.g. GIS.HistoricGeography ). Class
DBTableRecord stores the values of a record extracted from table Tables , i.e.
the description of a table (e.g. Routes ) belonging to the selected thematic
database. Class DBValueRecord stores the values of a record extracted from
the table identified by DBTableRecord , i.e. the description of route Via Appia .

15.5.3 Implementation

Classes MapEntity , MapEntitySet and MapLayer are extended with the data
structures that record the references to the tables and records in the
thematic databases and with the methods to store these references in an
XML file.

DBConnector

ArrayList keyList;
ArrayList labelList;

void openDatabase()
Iterator getDBList()
Iterator getTableList()
void loadTable()
DBValueRecord getRecord()

DBListRecord DBTableRecord DBValueRecord

int ID
String name
String description

long id;
long idDataBase;
String name;
String description;
String key;
String label;

ArrayList attributeList;
ArrayList typeList;
ArrayList valueList ;

Figure 15.10 The class diagram of the persistent layer