According to section “Maps and tables”, three main forms of using links between map features and table records can be singled out in ObjectLand:
Search and display of records linked with selected feature;
Search and display of features linked with selected record of linked table;
Usage of table data in filters.
In most cases the possibilities provided for the user do not depend on whether the link with internal GDB tables or with tables/queries of EDB is used. Each time it is required to make a choice between several tables or queries (for example, when opening a linked table or when working with feature information window), ObjectLand displays the tree of links which includes internal tables as well as tables and queries of EDB.
An important difference which cannot be fully avoided appears due to the fact that external databases can be situated either in opened or in closed state. If EDB is closed, ObjectLand knows about the presence of links of its tables/queries with map feature types, however it cannot use these links, since components of the closed EDB are inaccessible. Other difficulties may appear in the case if EDB is being closed when some windows which use links with it are still opened.
From the above said it is possible to single out some peculiarities of working with links which are referred to EDB.
When the windows which contain a tree of links of feature types (or of layer, theme or map) with tables and queries are being opened, components of closed EDBs are not displayed.
When commands which require selection from several tables or queries are called, components of closed EDBs are not taken into account.
If there are opened browser windows of linked tables or queries at the moment of closing EDB, these windows will be closed.
If the link with EDB table or query is used in filter condition of theme feature type, links between features and records of closed EDB are not taken into account when the condition is evaluated, that is, this case is equal to the one when there are no linked records available.
Figures 43-18 a, c show one and the same theme displayed in the case of opened and closed EDB which query is used in filter. The legend to the theme is shown at figure 43-18, b.
a) EDB is opened
b) Legend
c) EDB is closed
Figure 43-18. Filter with usage of EDB
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