ODBC tools are based on the notion of relational database consisting of the set of interconnected tables. In this connection tables and their representations (VIEWS in the terminology of SQL language) are main types of components of ODBC databases. The notion of view is close to the notion of the query used in ObjectLand.
Many database management systems also support additional types of components – synonyms (named links to other components), procedures and functions, triggers, etc.
GIS ObjectLand provides access to the following types of components of data sources:
tables;
system tables;
views;
synonyms (named links to other components).
When using EDB in ObjectLand all types of components mentioned above are considered to be EDB tables. Properties of these tables are mainly determined by peculiarities of used data sources.
Many EDBs support the conception of component owner. The notion of an owner allows controlling permissions to components from the part of EDB users in a more flexible way. GIS ObjectLand provides information about owners of EDB components.
It should be noted that user permissions to EDB components are in no way connected with permissions to GDB components described in the section “Access control” of the present manual. User permissions to GDB components are determined on the basis of identification of GDB user, when ObjectLand requests the user to enter the name and password at the time of opening the GDB (if there is a list of users available for this GDB, see chapter 85 “Access control basics”). Permissions to EDB components are determined on the basis of identification of the user in EDB – by user's name and password indicated when connecting to the data source (if the name and password are necessary for connection). User's names and passwords in GDB and EDB are not related to each other.
ObjectLand gets information about the present EDB components in the process of opening the EDB (right after establishing the connection). If the structure of EDB components is changed further with the help of means external to ObjectLand, these changes will become visible to ObjectLand user after closing and reopening the EDB.
In the process of receiving information about EDB components, ObjectLand determines possibilities of editing (adding, removing and modifying records) for each EDB component. The possibilities of editing tables and system tables are determined on the basis of user permissions to the corresponding component. Views are always considered to be accessible only for reading, since it is impossible to determine “editability” of view using ODBC tools. Synonyms are also considered to be accessible only for reading, because one cannot determine the type of component to which the synonym refers using ODBC tools.
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