Field attributes

Apart from type, each field is characterized by attributes. Attributes determine peculiarities of storing and editing field values.

The attribute “Indexed” means that the system will support the so-called index for this field. The presence of an index enables the system to execute search and sorting by such fields considerably quicker. Besides, indexes are used in table joins. However, all the fields should not be made indexed since the presence of indexes may result in considerable enlargement of GDB sizes. The field having an attribute “Indexed” will be called indexed field below.

While a table is modified (the operations of changing, removing, adding records are performed) the system automatically modifies all its indexes. Modification can lead to index “degeneration”. It means that the index performs its functions of providing a quick access to records much worse.

To evaluate the quality of an index an estimator called density and measured in percentage is introduced. The maximum value (100 per cent) corresponds to the best state of index. To evaluate and probably improve the index density the command Tools+Density should be used for selected table in the navigation window.

The attribute “Not empty” denotes that when adding or editing a record the present field should necessarily be filled in. The system will not allow an empty value in this field and will necessarily request the user to enter something.

The presence of the attribute “Unique” makes the system check uniqueness of field value, that is, absence of another record with the same field value in the table, before adding or editing a record. To quickly check the uniqueness of field value the system should have an index for it, that is why when specifying the attribute “Unique”, the attribute ”Indexed” is set automatically. On the other hand, since empty values in record fields break the requirement of uniqueness, the attribute “Not empty” is set automatically as well.

The attribute “Encrypted” means that table fields will be stored in GDB files in encrypted form. Using this attribute makes it practically impossible to view contents of the corresponding table field by means other than those of ObjectLand. At the same time working with a table containing encrypted fields in ObjectLand does not differ form working with a table which does not contain encrypted fields. The presence or absence of the attribute “Encrypted' for table fields in no way affects working with a table from the point of view of ObjectLand user.

Attribute	Purpose
Indexed	Building an index for a field. Speeding up the search, building joins and reference tables.
Not empty	Control of field not-emptiness in adding and editing.
Unique	Control of value uniqueness. Attributes “Indexed” and “Not empty” are set automatically.
Encrypted	Protection of table GDB information from reading it using program tools different from ObjectLand.