Domains

A domain is a pool of values from which users can choose when providing values for a type of attribute. A type of attribute may be stored in multiple columns. These columns are said to be based on the domain.

A domain is a rich data type. In addition to delimiting a pool of values, it also specifies other key aspects of columns based on the domain. For example, it may specify in which format the Rules Engine is to present stored date/time values to the user, or which type of visual control must be used in the screen for columns based on the domain.

A domain containing all-uppercase alphabetic strings with a maximum length of 60, such as 'SMITH', could be used for attributes that are customer names.

A domain containing integers in the range 0-100 could be used for attributes that are percentages. The domain could specify that these integers must be shown in a Slider control that allows users to "spin" quickly to the desired value.

'Domain' is one of the fundamental concepts of the USoft Definer model. Perhaps the primary purpose of a domain is to communicate to the RDBMS what is the desired datatype and data length of each column. In this capacity, a USoft domain is the equivalent of 'NUMBER( 8, 2 )' or 'VARCHAR( 256 )' clauses in traditional CREATE TABLE or ALTER TABLE statements.

But USoft domains serve many more purposes. They allow you to:

•Build a highly consistent data model by inviting you to re-use, where possible, column characteristics for like columns across your entire model.

•Check that only allowed values are admitted to the database.

•Handle default values and predefined data formats. Dates and times are examples of data where predefined data formats are important.

•Generate unique values that can act as a handle for identifying individual data records.

A domain is defined by a number of name-value pairs describing aspects of data values of a specific type.

A domain has a unique name. Each column based on the domain is linked to it by specifying the domain name for the column. Each USoft column must be based on exactly 1 domain.

Some domain settings are propagated to the RDBMS so that the RDBMS can create a physical column with the appropriate datatype.

Other domain settings have a technical effect in the USoft layer only. If your domain has allowed values, the Rules Engine and not the RDBMS checks that each input value is among the allowed values.

Finally, some domain settings affect the default USoft GUI for fields based on the column(s) that are based on the domain. If your domain has "Display Type" = "Dropdown List Box", possible field values to choose from are presented in a dropdown list box.

For details on domain attributes, click on one of the See also links below.