The presence of ODBC drivers for different data formats provides the users with a possibility of standard access to the corresponding EDB types. Such a driver should provide standard program interface of access to data based on using the SQL language of requests to data and hiding specific character of working with some particular DBMS. At present there are ODBC drivers practically for all known DBMS available on the software market. In some cases there is a possibility to choose ODBC driver from a great number provided by different manufacturers.
To organize access to EDB the application should pass the information about connection with EDB to ODBC driver. Such information can include location of EDB server, the folder where data files are located (in case of “desktop” database management systems), name and password of EDB user and also some additional parameters determining modes of connection with EDB. In ODBC terminology the driver and data about connection with EDB determine the data source.
Since indication of some particular ODBC driver of EDB and passing all the information to it specific for connection with some concrete EDB makes application not so universal, ODBC provides a possibility to create named data sources. Named data source is a description of ODBC driver and the data about connection with EDB stored under some specified name (DSN – Data Source Name) or in Windows registry, or in the form of a file in some local area network (LAN) folder accessible for all users. A special utility called ODBC Administrator is provided by Windows to be able to create named data sources and change their settings.
GIS ObjectLand permits the user to add an EDB by indicating ODBC driver and specifying the data for the connection, as well as on the basis of named data source. Apart from that, GIS ObjectLand provides a possibility of calling ODBC administrator when working with GDB.
It should be noted that EDB plays the role of one of GDB components in GIS ObjectLand. Description of the data source is stored in GDB either all the time or during the session of working with GDB. To be able to store the description of the data source in GDB permanently it is required to save the EDB in GDB under some unique name after adding it. It is possible to specify autoopening mode for saved EDBs which allows setting connection with the data source automatically when the GDB is opened (the user might be asked to enter the name and password to establish the connection).
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