Since ObjectLand is a geoinformation system, not just information system, independent use of tables in isolation from spatial GDB data is rarely justified. The main purpose of tables in ObjectLand is storing information about map features.
Setting links between map features and table records is one of the most important means of ObjectLand.
ObjectLand permits linking any type of features with one or several tables. Such a link means that it is possible to associate records in the table possessing some information about the present feature with particular features.
Let's take an example. There is a feature type “Parcel” in the map “N-City” of the GDB City, and among the tables of this GDB – the table “Parcel owners”. A link between the feature type “Parcel” and a table “Parcel owners” can be set. It gives a possibility to set links between features and table records: any parcel can be linked with the table record which contains name and other data about the owner of this parcel. On the other hand, the same parcel can be linked, for example, with the table record “Parcel certificates”, and this link does not depend on the link with owners: the parcel's owner can be changed but the certificate may remain or vice versa.
A link between feature type and a table can be specified as unique or as a multiple one. In the case of a unique link, every particular feature of the present type can be linked only with one table record (or can have no links at all). A multiple link allows one feature to be linked with arbitrary number of records of one and the same table. Let's suppose that every feature of the type “Block” is linked with those records of the table “Building certificates” which describe buildings located in this block of buildings. Since several buildings can be located in one block, the link between blocks and building certificates should be specified as a multiple one.
One should have in mind that any number of features of one and the same type or of different types can be linked with one and the same table record not depending on whether the links between feature types and the present table are unique or multiple.
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