Editing Object Constraint Language (section)

== Alternatives ==
Being a rule-based validation language, [[Schematron]] may be considered an alternative to OCL. However Schematron works for Extensible Markup Language [[XML tree|(XML) tree]]s while OCL makes it possible to navigate [[Meta-Object Facility|MOF]]-based models and meta-models (i.e. XML Metadata Interchange ([[XML Metadata Interchange|XMI]]) trees). In other words, OCL relates to UML or MOF similarly to how Schematron relates to [[XML]]. (Note that Schematron uses [[XPath]] to navigate inside the XML trees.)<br>Being a model specification language permitting designers to decorate a model or a meta-model with side-effect-free annotations, OCL could be replaced by languages like [[Alloy language|Alloy]]. Automated OCL generation is in principle possible from natural language.<ref name="NL2OCL">{{cite journal| author=Imran Sarwar Bajwa|title=OCL Constraints Generation from Natural Language Specification, 2010|publisher =[[IEEE]]|date=October 2010|doi=10.1109/EDOC.2010.33|s2cid=7495256}}</ref>

{| class="wikitable"
|+ Examples
!Constraint
!OCL Equivalent
|-
|The age of a person is not negative.
|<code>'''context''' Person '''inv''': self.age >=0</code>
|-
|A person is younger than its parents.
|<code>'''context''' Person '''inv'''<nowiki>: self.parents->forAll(p|p.age>self.age)</nowiki></code>
|-
|After a birthday, a person becomes one year older.
|<code>'''context''' Person::hasBirthday() '''post''': self.age=self.age@pre+1</code>
|-
|A Person has 2 parents at max.
|<code>'''context''' Person '''inv''': self.parents->size()<=2</code>
|-
|After somebody has a child, his/her child-set is not empty, and it is larger than before.
|<code>'''context''' Person::getsChild() '''post''': self.childs->notEmpty() and self.childs->size() > self.childs@pre->size()</code>
|-
|Only an adult can be owner of a car.
|<code>'''context''' Person '''inv''': self.age<18 '''implies''' self.cars->isEmpty()</code>
|-
|The first registration of a car can not be before it is built.
|<code>'''context''' Auto '''inv''': self.registration>=self.constructionYear</code>
|-
|Every Person that has a car has at least one car which is younger than the Person.
|<code>'''context''' Person '''inv''': self.cars->notEmpty() '''implies'''<nowiki> self.cars->exists( c | </nowiki>'''Calendar.YEAR''' - c.constructionYear < self.age)</code>
|-
|Nobody can be his/her own parent.
|<code>'''context''' Person '''inv''': self.parents->excludes(self)</code>
|-
|There's at least one Person which owns a car.
|<code style="white-space: nowrap">'''context''' Person '''inv'''<nowiki>: Person.allInstances()->exists(p | p.cars->size() > 0)</nowiki></code>
|}
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