OCL in a small nutshell

1
OCL in a small nutshell

• Jairson Vitorino, Cin UFPE
• May, 2nd 2005

2
Contents

• Motivation
• What is OCL?
• Uses of OCL
• Examples
• References

3
Motivation

• Are you serious about your UML models?
• (source www.empowertec.de)

4
What is OCL?

• The Object Constraint Language (OCL) is a query
  language that can be used to define expressions
  on object oriented models (UML).
• OCL enrich the models with unambiguous
  information, formalizing knowledge about the
  underlying business domain.

5
It is a formal language, but Yes! You can
understand it and even use it!
6
Uses of OCL

• Constraints are the most prominent use.
• Initialization expressions can be used to specify
  an initial value for an attribute or an
  association.
• OCL expressions can be used to specify the
  algorithm that is to be used for derived
  attributes, i.e. values that are calculated from
  other attributes or associations.
• OCL expressions can be used to specify the
  implementation of methods as long as they do not
  have side effects (i.e. the method is 'read
  only').

7
A trivial Example
optional
You can refer to the previous state of na object
context Stackpop() Object pre notEmpty
isEmpty() false post topElementReturned
result self_at_pre.top() post topElementRemoved
top() ltgt self_at_pre.top()   context Stacktop()
Object pre notEmpty isEmpty() false  
context Stackpush(anObject Object) void
post pushedObjectIsOnTop top() anObject
8
A more typical example
9
And typical constraints...
No employee may be older than 65 years
OCL equivalent
context Company inv self.employee-gtforAll(age lt
65)
And what about this one? What does it mean?
context Company inv employee-gtexists(isUnemploye
d) false
10
More examples in the PDF
11
Tools

• Octopus Plug-in for Eclipse
• (syntatical checking on class diagrams, cool
  editor and generates java code!)
  http//www.klasse.nl/english/research/octopus-intr
  o.html
• OCLE
• From Romenia, syntantical checking, model
  checking, comes with full UML meta-model and
  well-formdness rules for diagrams consistency in
  OCL! Generates java code) http//lci.cs.ubbcluj.ro
  /ocle/overview.htm
• OCL-AddIn for Rational Rose, similar to Octopus
  but do not generate code.
• http//www.empowertec.de/products/rational-rose-oc
  l.htm

12
Conclusions and further motivation

• UML without OCL is only useful for extreme
  programming, disposable models
• OCL is key for formal methods, UML models as
  first-class, strategic, reusable artefacts and
  (future) automated code generation

13
References

• http//www.omg.org
• http//www.empowertec.de
• Presentation Object Constraint Language (OCL) by
  Tevfik Bultan (www.cs.ucsb.edu/bultan/courses/272
  /OCL.ppt)
• Introduction to OCL, Andreas Roth
• (i12www.ira.uka.de/aroth/ lehre/keypraktWS0304/oc
  lIntro.pdf)