Object Constraint Language

The Object Constraint Language (OCL) is a declarative language for describing rules that apply to Unified Modeling Language (UML) models developed at IBM and now part of the UML standard. Initially, OCL was only a formal specification language extension to UML.^[1] OCL may now be used with any Meta-Object Facility (MOF) Object Management Group (OMG) meta-model, including UML.^[2] The Object Constraint Language is a precise text language that provides constraint and object query expressions on any MOF model or meta-model that cannot otherwise be expressed by diagrammatic notation. OCL is a key component of the new OMG standard recommendation for transforming models, the Queries/Views/Transformations (QVT) specification.

Description

OCL is a descendant of Syntropy, a second-generation object-oriented analysis and design method. The OCL 1.4 definition specified a constraint language. In OCL 2.0, the definition has been extended to include general object query language definitions.

OCL statements are constructed in four parts:

a context that defines the limited situation in which the statement is valid
a property that represents some characteristics of the context (e.g., if the context is a class, a property might be an attribute)
an operation (e.g., arithmetic, set-oriented) that manipulates or qualifies a property, and
keywords (e.g., if, then, else, and, or, not, implies) that are used to specify conditional expressions.

Relation

OCL and UML

OCL supplements UML by providing expressions that have neither the ambiguities of natural language nor the inherent difficulty of using complex mathematics. OCL is also a navigation language for graph-based models.

OCL and MOF

OCL makes a Meta-Object Facility model more precise by associating assertions with its meta-elements.

OCL and QVT

Of particular importance to Model Driven Engineering (MDE) or model-driven architecture is the notion of Model transformation. The OMG has defined a specific standard for model transformation called MOF/QVT or in short QVT. Several model transformation languages like GReAT, VIATRA, or Tefkat are presently available, with different levels of compliance with the QVT standard. Many of these languages are built on top of OCL, which is the main part of the QVT-compliance.

Alternatives

Being a rule-based validation language, Schematron may be considered an alternative to OCL. However Schematron works for Extensible Markup Language (XML) trees while OCL makes it possible to navigate MOF-based models and meta-models (i.e. 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.)
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. Automated OCL generation is possible through Natural Language like NL2OCL.

References

↑ Object Management Group (OMG); Object Constraint Language Specification, Chapter 7 of OMG Unified Modeling Language Specification, Version 1.3, March 2000 (first edition)
↑ Object Management Group (OMG); Object Constraint Language OMG Available Specification Version 2.0, May 2006

External links

OMG OCL specification
OCL Portal - The center for OCL related information
OCL page of Computer Science Dept. of CSUSB (brief OCL 2.0 syntax)
Octopus: OCL Tool for Precise Uml Specifications (OCL checker)
Dresden OCL Toolkit (OCL Toolkit, various OCL related publications)
HOL-OCL (An interactive theorem proof environment for OCL, various OCL related publications)
OCL for Java tutorial on ParlezUML
Article on using EMF's OCL in Java code
UML link page on cetus-links.org
USE (UML-based Specification Environment) (OCL Tool for model validation, various OCL related publications)
OCL tutorial
NL2OCL (OCL Tool for invariant generation from NL)

Query languages

In current use	.QL ALPHA CQL Cypher D DMX Datalog Gremlin ISBL LDAP LINQ MQL MDX OQL OCL QUEL SMARTS SPARQL SQL XQuery XPath

Proprietary	YQL

Superseded	CODASYL

ISO standards by standard number

List of ISO standards / ISO romanizations / IEC standards

1–9999	1 2 3 4 5 6 7 9 16 31 -0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 128 216 217 226 228 233 259 269 302 306 428 518 519 639 -1 -2 -3 -5 -6 646 690 732 764 843 898 965 1000 1004 1007 1073-1 1413 1538 1745 1989 2014 2015 2022 2047 2108 2145 2146 2240 2281 2709 2711 2788 2852 3029 3103 3166 -1 -2 -3 3297 3307 3602 3864 3901 3977 4031 4157 4217 4909 5218 5428 5775 5776 5800 5964 6166 6344 6346 6385 6425 6429 6438 6523 6709 7001 7002 7098 7185 7200 7498 7736 7810 7811 7812 7813 7816 8000 8178 8217 8571 8583 8601 8632 8652 8691 8807 8820-5 8859 -1 -2 -3 -4 -5 -6 -7 -8 -8-I -9 -10 -11 -12 -13 -14 -15 -16 8879 9000/9001 9075 9126 9293 9241 9362 9407 9506 9529 9564 9594 9660 9897 9899 9945 9984 9985 9995

10000–19999	10006 10116 10118-3 10160 10161 10165 10179 10206 10218 10303 -11 -21 -22 -28 -238 10383 10487 10585 10589 10646 10664 10746 10861 10957 10962 10967 11073 11170 11179 11404 11544 11783 11784 11785 11801 11898 11940 (-2) 11941 11941 (TR) 11992 12006 12182 12207 12234-2 13211 -1 -2 13216 13250 13399 13406-2 13407 13450 13485 13490 13567 13568 13584 13616 14000 14031 14224 14289 14396 14443 14496 -2 -3 -6 -10 -11 -12 -14 -17 -20 14644 -1 -2 -3 -4 -5 -6 -7 -8 -9 14649 14651 14698 -2 14750 14764 14882 14971 15022 15189 15288 15291 15292 15398 15408 15444 -3 15445 15438 15504 15511 15686 15693 15706 -2 15707 15897 15919 15924 15926 15926 WIP 15930 16023 16262 16612-2 16750 16949 (TS) 17024 17025 17203 17369 17799 18000 18004 18014 18245 18629 18916 19005 19011 19092 (-1 -2) 19114 19115 19125 19136 19439 19500 19501 19502 19503 19505 19506 19507 19508 19509 19510 19600 19752 19757 19770 19775-1 19794-5 19831

20000+	20000 20022 20121 21000 21047 21500 21827:2002 22000 23270 23271 23360 24517 24613 24617 24707 25178 25964 26000 26300 26324 27000 series 27000 27001:2005 27001:2013 27002 27003 27004 27005 27006 27007 27729 27799 28000 29110 29148 29199-2 29500 30170 31000 32000 38500 40500 42010 80000 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14

Categories	ISO standards ISO 639 ISO 3166 ISO / IEC standards OSI protocols

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This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

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