Similar to normal database applications, Documentum supports constraints to enforce while creating or modifying any instances of object types.
Constraints are stored in the content server but they are not used by the repository except few cases. These constraints are enforced by the client applications.
Unique Key: A unique key identifies a property or combination of property of an object instance to be unique. Unique key can be combined either with single valued attributes or with repeating valued attributes. Combination of single valued and repeating value is not possible because single valued and repeating valued attributes are stored in different tables and is not possible by any relational database to apply a unique across two tables.
Primary Key: Primary key constraint is similar to unique key except it does not support NULL values. Primary key can be combined with single valued properties. Repeating values are not allowed for primary key constraint.
Foreign Key: A foreign key is a referential between two object types. The foreign key identifies a column or a set of columns in one table that refers to a column or set of columns in another table. Foreign key cannot be applied on to two different data types. Foreign key constraint can be combination of one or more single valued or repeating valued attributes. Combination of single valued and repeating valued are not allowed.
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