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Identifier Selection Statements

Statements

IdentifierSelection

IdentifierKey

KeySelection

NullKeySelection

General

IdentifierSelection statements allow a specific object to be found from the objects that belong to an entity using identifying attributes.

The Model Compiler should use the underlying mechanisms and facilities available to make any search as efficient as possible and certainly more efficient than if the same functionality was written in the equivalent primitive statements.

Typically, the values used in the search originate from the Real World as event data.

Once the object has been found it can be manipulated as required and new relationships can be formed. A new relationship can be established with the object through use of the Relate statement; when this is done the IdentifierSelection statement is no longer required as the object is simply accessed via the Traverse statement. The object in the new relationship must belong to a non-identifying entity as the searched for object must already have a relationship with an identifying object.

Associated Statements

The IdentifierSelection statements are used with the following Identifier statements:

Identifier

OwnKey

ForeignKey

An identifier is declared by the Identifier statements and actioned by the IdentifierSelection statements.

IdentifierSelection Statement

StateAction

IdentifierSelection:Dog:Dog_Identifier

IdentifierKey

Dog       : Name : Dog_name

Dog_Owner : Name : Dog_owner_name

KeySelection

| This subregion in the single context of the Dog.

NullKeySelection

| No Dog was found with the supplied identifying values.

The IdentifierSelection statement introduces the IdentifierKey, KeySelection and NullKeySelection  statements.

IdentifierKey Statement

StateAction

IdentifierSelection:Dog:Dog_Identifier

IdentifierKey

Dog       : Name : Dog_name

Dog_Owner : Name : Dog_owner_name

KeySelection

| This subregion in the single context of the Dog.

The IdentifierKey statement's data subregion specifies the values to be used for the identifying attributes. The attributes may belong to the searched entity or to a foreign entity. The fields of the data region are: name of the entity, name of the identifying attribute, name of data item containing the value to be matched.

KeySelection Statement

StateAction

IdentifierSelection:Dog:Dog_Identifier

IdentifierKey

Dog       : Name : Dog_name

Dog_Owner : Name : Dog_owner_name

KeySelection

| This subregion in the single context of the Dog.

The KeySelection statement provides a subregion where the found object is in context.

NullKeySelection Statement

StateAction

IdentifierSelection:Dog:Dog_Identifier

IdentifierKey

Dog       : Name : Dog_name

Dog_Owner : Name : Dog_owner_name

NullKeySelection

| No Dog was found with the supplied identifying values.

If no object exists with the identifying attribute values specified, the statements in the NullKeySelection subregion are executed.

Identifier Selection Example

Declare Dog Owner entity:

Entity:Dog_Owner

Attribute

Text : Name

Identifier:Dog_Owner_Identifier

OwnKey

Name

Declare Dog entity:

Entity:Dog

Attribute

Text : Name

Relationship

Belongs_to --> Dog_Owner

Identifier:Dog_Identifier

OwnKey

Name

ForeignKey

Belongs_to : Dog_Owner : Dog_Owner_Identifier

The IdentifierSelection statement does not depend on the context and can be used anywhere:

StateAction

IdentifierSelection:Dog:Dog_Identifier

IdentifierKey

Dog       : Name : Dog_name

Dog_Owner : Name : Dog_owner_name

KeySelection

| This subregion in the single context of the Dog.

Template

<<:>>The identifying values for the Dog found are:

<<:>>    <<#Dog.Name>> / <<#Dog_owner_name>>

NullKeySelection

| This subregion in the original state action context.

Template

<<:>>No Dog was found with the identifying values:

<<:>>    <<#Dog_name>> / <<#Dog_owner_name>>