Model Definition > Attributes

A Ventity™ attribute is a property or characteristic of an entity. Like variables, each attribute of an entity type has a name (e.g. "hair color") and a value (e.g. "brown"). Unlike variables, whose values are numbers, the value of an attribute is a string -- any combination of letters, numbers, or other characters.

Key Attributes

Each non-singular entity is uniquely identified by one to four attributes that are identified as key attributes. Once an entity is created, key attribute values cannot be changed.

Key attributes may also be used in logical expressions, relationship definition, and sub-collection definition.

Other Attributes

The initial values for other attributes are set during entity initialization, either from input data or during a Create Action.

These values may be changed using assignments performed by actions. Values may be assigned explicit string values, such as "READY" or they may be set to equal the value of another attribute.

Use in logical expressions:

Attribute values may be compared to literal strings or to other attribute values. Logical expressions may be used in model equations , in trigger conditions, and in a variety of action control statements.

Attribute comparisons are case insensitive. Thus, TRUE, true, and True are treated as the same value.

Relationships

Attributes can provide connections to other entities by matching the attribute value with entity key values. When a target entity has more than one key, a Reference must be defined.

Sub-Collections

Attributes from an entity can be used to define sub-collections of that entity type. Sub-collections contain all of the entities within a collection that have the same values for all key attributes. If an attribute value that is used for sub-collection membership is changed, the entity is removed from the current sub-collection and added to a new or existing sub-collection with the appropriate key values.