Attribute Constraints

Attribute constraints regard attributes associated with object or protocol classes.

Attribute cardinality constraints specifying the minimum and maximum number of values for attributes. If the attribute cardinality constraint is not specified, then it is by default [0,1] for single-valued attributes, and [0,] for set-valued or list-valued attributes, where an unspecified maximum represents an unlimited number of values.

<cardinality> ::= [ <min> , <max> ] |
                | [ <min> , ] |
                | <null>
                ;
<min> ::= /* a positive integer or zero */
        ;
<max> ;;= /* a positive integer */
        ;

Note that component attributes of a tuple attribute can have their own cardinality constraints (i.e., [0,1] or [1,1]) that are different from the cardinality constraints for the tuple attribute. A cardinality constraint for a component attribute specifies whether the value of this attribute can or cannot be null.

Referential integrity constraints are implied by an OPM schema and regard abstract attributes or attributes associated with controlled value classes; the values of such attributes must belong to their associated value classes.

Inversion constraints are explicitly specified in an OPM schema and regard pairs of abstract non-derived attributes. We use below the following notation: if A denotes an attribute of object or protocol class and x denotes an object instance of , then denotes the set of A values for x. Only single-valued or set-valued attributes can be associated with inverse constraints, list-valued attributes cannot have inverses. Note that inverse constraints are not allowed in an OPM schema that supports permission model.

A simple or component attribute A of object or protocol class can be defined as the inverse of a simple attribute B of object or protocol class iff

1. A and B are not associated with any derivation;

2. A is associated with a single abstract value class ; and

3. the value class associated with B, , includes .

<inverse constraint> ::= inverse of <class name> . <simple attribute name>
                       | <null>
                       ;
<component inverse constraints> ::= <comp inverse constraint> | <null>
                                  ;
<comp inverse constraint> ::= <comp attribute name> inverse of
                              <class name> . <simple attribute name>
                            | <comp inverse constraint> ,
                              <comp attribute name> inverse of
                              <class name> . <simple attribute name>
                            ;

The following object class definitions contain examples of attribute constraints:

OBJECT CLASS CHROMOSOME
   ID: chromosome_nr 
   ATTRIBUTE chromosome_nr: [1,1] INTEGER
                            DESCRIPTION: "chromosome number"
                            EXAMPLE: "19"
   ATTRIBUTE has_map: set-of [0,] MAP
                      inverse of MAP.has_chromosome
OBJECT CLASS MAP
   ID: map_name
   ATTRIBUTE map_name: [1,1] VARCHAR (80) 
                       DESCRIPTION: "map name"
   ATTRIBUTE has_chromosome: set-of [0,] CHROMOSOME
                             inverse of CHROMOSOME.has_map