Module Documentation: eml-constraint

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The eml-constraint module - Relationships among and within dataset entities

The eml-constraint schema defines the integrity constraints between entities (e.g., data tables) as they would be maintained in a relational management system. These constraints include primary key constraints, foreign key constraints, unique key constraints, check constraints, and not null constraints, among potential others.

Module details

Recommended Usage: All datasets where there are logical constraints between entities
Stand-alone: no
Imports: eml-documentation, eml-resource
Imported By:
View an image of the schema: eml-constraint image

Element Definitions:

primaryKey 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ConstraintBaseGroup  
keyrequired
)
The primaryKey element declares the primary key in the entity to which the defined constraint pertains.
Example(s):
date
site

key 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
attributeReferencerequiredunbounded
)
The key element defines the set of attributes to which this constraint applies. For a primary key or a unique key, the set of attributes must be identifying. For a foreign key, the set of attributes must match an identifying key in the referenced entity. For a 'not null' constraint, the key indicates the attribute which should not be null.
Example(s):
site
plot

attributeReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The attributeReference element is the identifier of an attribute that can be found in the identified entity. This id will be unique within an entity and specifies that the attribute participates in the key that is being defined.
Example(s):
site

uniqueKey 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ConstraintBaseGroup  
keyrequired
)
The uniqueKey element represents a unique key within the referenced entity. This is different from a primary key in that it does not form any implicit foreign key relationships to other entities, however it is required to be unique within the entity.
Example(s):
date

key 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
attributeReferencerequiredunbounded
)
The key element defines the set of attributes to which this constraint applies. For a primary key or a unique key, the set of attributes must be identifying. For a foreign key, the set of attributes must match an identifying key in the referenced entity. For a 'not null' constraint, the key indicates the attribute which should not be null.
Example(s):
date, site, plot

attributeReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The attributeReference element is the identifier of an attribute that can be found in the identified entity. This id will be unique within an entity and specifies that the attribute participates in the key that is being defined.
Example(s):
site

checkConstraint 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ConstraintBaseGroup  
checkConditionrequired
)
Attributes: Use: Default Value:
languageoptional
The checkConstraint element defines a constraint which checks a conditional clause within an entity.
Example(s):
if site>1 then plot>10

checkCondition 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The checkCondition element defines an SQL statement or other language implementation of the condition for a check constraint. Generally this provides a means for constraining the values within and among entities.
Example(s):
(year > 1900 and year < 1990)

foreignKey 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
The foreignKey element defines a foreign key relationship among entities which relates this entity to another's primary key.

joinCondition 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ForeignKeyGroup  
referencedKeyrequired
)
The joinCondition element describes any join of two tables that is not done with a primary/foreign key relationship.
Example(s):
JOIN code

referencedKey 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
attributeReferencerequiredunbounded
)
The referencedKey element defines set of attributes to which a foreign key constraint refers. If the key refers to the primary key in the referenced entity, then the "referencedKey" is optional. For a foreign key, the set of attributes must match an identifying key in the referenced entity.
Example(s):
site, plot

attributeReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The attributeReference element is the identifier of an attribute that can be found in the identified entity. This id will be unique within an entity and specifies that the attribute participates in the key that is being defined.
Example(s):
site

notNullConstraint 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ConstraintBaseGroup  
keyrequired
)
The notNullConstraint element defines a constraint that indicates that no null values should be present for an attribute in this entity.

key 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
attributeReferencerequiredunbounded
)
The key element defines the set of attributes to which this constraint applies. For a primary key or a unique key, the set of attributes must be identifying. For a foreign key, the set of attributes must match an identifying key in the referenced entity. For a 'not null' constraint, the key indicates the attribute which should not be null.

attributeReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The attributeReference element is the identifier of an attribute that can be found in the identified entity. This id will be unique within an entity and specifies that the attribute participates in the key that is being defined.
Example(s):
site

constraintName 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The constraintName element is a name which represents a human readable and meaningful name for the constraint.
Example(s):
PrimaryKey_birdSurvey

constraintDescription 

This element has no default value.
Content of this field: Description of this field:
The constraintDescription element describes the nature of the constraint. It might be a description of a check condition, or a statement about the composition of a primary key or the nature of the relationship between two database tables or two ascii files.
Example(s):
1.Must be greater than 0 but less than 100 2. "The primary key of the table BIRD_SURVEY is composed of two attributes:speciesCode and observationDate 3. The species name associated with the species code in survey.txt can be found in the file speciesList.txt

key 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
attributeReferencerequiredunbounded
)
The key element defines the set of attributes to which this constraint applies. For a primary key or a unique key, the set of attributes must be identifying. For a foreign key, the set of attributes must match an identifying key in the referenced entity. For a 'not null' constraint, the key indicates the attribute which should not be null.

attributeReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The attributeReference element is the identifier of an attribute that can be found in the identified entity. This id will be unique within an entity and specifies that the attribute participates in the key that is being defined.
Example(s):
site

entityReference 

This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The entityReference element contains the id of the entity to which a foreign key refers, otherwise known as the parent-entity or parent-table. This should be an identifier that matches one of the "identifier" elements for an entity.
Example(s):
knb.79.4

relationshipType 

This element has no default value.
Content of this field: Description of this field:
The relationshipType element defines identifying relationships that propagate from the parent entity's primary key to the child's primary key. Non-identifying relationships propagate the parent's primary key as a non-key attribute of the child entity.
Example(s):
relationshipType code

Derived from: xs:string (by xs:restriction)

Allowed values:

  • identifying
  • non-identifying

cardinality 

This element has no default value.
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
parentOccurencesrequired
childOccurencesrequired
)
The cardinality element represents a statement of the relationship between parent and child entities. Cardinality is expressed as the ratio of related parent and child entities. Cardinality 1 to N is a specific form of cardinality in which zero or one parent records are related to a specified number of child records. The cardinality ratio for the parent entity depends on whether the "existence" is mandatory (one or more) or optional (zero to ...).
Example(s):
One to many
One to 10
Zero or One to Many

parentOccurences 

This element has no default value.
Content of this field: Description of this field:
The parentOccurences element describes the Parent portion of a 1 to exactly N cardinality. May have a value of either 0 or 1. Value of 0 implies that the "existence" of a child record is optional. Value of 1 implies that the "existence" of a child record is mandatory.
Example(s):
One to 10, Zero or One to Many

Derived from: xs:integer (by xs:restriction)

Allowed values:

  • 0
  • 1

childOccurences 

This element has no default value.
Content of this field: Description of this field:
Type: CardinalityChildOccurancesType
The childOccurences element describes the child portion of a cardinality expression Allowed values are positive integers including zero or the string value "many"
Example(s):
2, 15, many

Attribute Definitions:

language

Type: xs:string

Use: optional

The language element declares the language that is used to implement the check constraint. This is typically the name and version of a programming language such as Java, C, Perl, Basic, or other. Sometime it is the name and version of a scriptable analysis system such as SAS, Matlab, R, or SPlus.
Example(s):
Perl 5.6.1

id

Type: res:IDType

Use: optional

system

Type: res:SystemType

Use: optional

scope

Type: res:ScopeType

Use: optional

Default value: document

Complex Type Definitions:

ConstraintType 

Content of this field: Description of this field:
Elements: Use: How many:
A choice of (
primaryKeyrequired
OR
uniqueKeyrequired
OR
checkConstraintrequired
OR
foreignKeyrequired
OR
joinConditionrequired
OR
notNullConstraintrequired
)
Attributes: Use: Default Value:
idoptional
systemoptional
scopeoptionaldocument
The ConstraintType type describes the relational integrity constraints of a relational database. This includes primary keys, foreign keys, unique keys, etc. When an eml-constraint module is created, it should be linked into a dataset using the "triple" element, and all of the entities that are referenced in the constraints should be accessible within that same package.

Simple Type Definitions:

CardinalityChildOccurancesType

The CardinalityChildOccurancesType element defines the child portion of a cardinality expression. Allowed values are positive integers including zero or the string value "many".
Example(s):
0,1, 2, 15,many

Group Definitions:

ConstraintBaseGroup 

Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
constraintNamerequired
constraintDescriptionoptional
)

ForeignKeyGroup 

Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
ConstraintBaseGroup  
keyrequired
entityReferencerequired
relationshipTypeoptional
cardinalityoptional
)

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