The Object Constraint Language Getting Your Models Ready for MDA

by Warmer, Jos; Kleppe, Anneke

• ISBN13: 9780321179364
• ISBN10: 0321179366
• Edition: 2nd
• Format: Paperback
• Copyright: 2003-08-27
• Publisher: Addison-Wesley Professional

Summary

bull; Learn to better leverage the siginificant power of UML 2.0 and the Model-Driven Architecture standard bull; The OCL helps developers produce better software by adding vital definition to their designs bull; Updated to reflect the latest version of the standard - OCL 2.0

Author Biography

Jos Warmer is the primary author of the OCL standard. He is an active member of the Unified Modeling Language (UML) Revision Task Force Anneke Kleppe is a consultant and adviser at Klasse Objecten, which she founded in 1995

Table of Contents

List of Figures	xv
List of Tables	xvii
Foreword to the First Edition	xix
Foreword to the Second Edition	xx
Preface and Introduction	xxiii
Who Should Read This Book	xxiv
How This Book Should Be Used	xxiv
Typeface Conventions	xxiv
Information on Related Subjects	xxv
Acknowledgments	xxv
Part 1 User Manual	1	(104)
Chapter 1 MDA and the Use of OCL	3	(18)
1.1 Introducing OCL	3	(1)
1.2 Model Driven Architecture	4	(5)
1.2.1 PIMs and PSMs	4	(1)
1.2.2 Automation of Transformations	5	(1)
1.2.3 MDA Building Blocks	5	(2)
1.2.4 MDA Benefits	7	(1)
1.2.5 The Silver Bullet?	8	(1)
1.3 Modeling Maturity Levels	9	(3)
1.3.1 Level 0: No Specification	9	(1)
1.3.2 Level 1: Textual	10	(1)
1.3.3 Level 2: Text with Diagrams	11	(1)
1.3.4 Level 3: Models with Text	11	(1)
1.3.5 Level 4: Precise Models	11	(1)
1.3.6 Level 5: Models Only	12	(1)
1.4 Building Better Models	12	(3)
1.4.1 Why Combine UML and OCL?	12	(2)
1.4.2 Value Added by OCL	14	(1)
1.5 Characteristics of OCL	15	(3)
1.5.1 Both Query and Constraint Language	16	(1)
1.5.2 Mathematical Foundation, But No Mathematical Symbols	17	(1)
1.5.3 Strongly Typed Language	17	(1)
1.5.4 Declarative Language	18	(1)
1.6 Summary	18	(3)
Chapter 2 OCL By Example	21	(16)
2.1 The "Royal and Loyal" System Example	21	(3)
2.2 Adding Extra Information	24	(3)
2.2.1 Initial Values and Derivation Rules	24	(1)
2.2.2 Query Operations	25	(1)
2.2.3 Defining New Attributes and Operations	26	(1)
2.3 Adding Invariants	27	(2)
2.3.1 Invariants on Attributes	27	(1)
2.3.2 The Type of the Attribute Is a Class	27	(1)
2.3.3 Invariants on Associated Objects	27	(1)
2.3.4 Using Association Classes	28	(1)
2.3.5 Using Enumerations	29	(1)
2.4 Working with Collections of Objects	29	(4)
2.4.1 Using Collections Operations	29	(3)
2.4.2 Sets, Bags, OrderedSets, and Sequences	32	(1)
2.5 Adding Preconditions and Postconditions	33	(2)
2.5.1 Simple Preconditions and Postconditions	33	(1)
2.5.2 Previous Values in Postconditions	34	(1)
2.5.3 Messaging in Postconditions	34	(1)
2.6 Taking Inheritance into Account	35	(1)
2.7 Comments	35	(1)
2.8 Let Expressions	36	(1)
2.9 Summary	36	(1)
Chapter 3 Building Models with OCL	37	(34)
3.1 What Is a Model?	37	(3)
3.1.1 Definitions	37	(1)
3.1.2 A Model Is a Consistent, Coherent Unit	38	(1)
3.1.3 The Context of an OCL Expression	38	(2)
3.2 Use UML Diagrams as a Base	40	(1)
3.3 Completing Class Diagrams	40	(10)
3.3.1 Derivation Rules	40	(1)
3.3.2 Initial Values	41	(1)
3.3.3 Body of Query Operations	41	(1)
3.3.4Invariants	41	(1)
3.3.5 Preconditions and Postconditions	42	(3)
3.3.6 Messaging in Postconditions	45	(1)
3.3.7 Cycles in Class Models	46	(1)
3.3.8 Defining Derived Classes	47	(2)
3.3.9 Dynamic Multiplicity	49	(1)
3.3.10 Optional Multiplicity	49	(1)
3.3.11 Or Constraints	49	(1)
3.4 Completing Interaction Diagrams	50	(4)
3.4.1 Instances	51	(2)
3.4.2 Conditions	53	(1)
3.4.3 Actual Parameter Values	54	(1)
3.5 Completing Statecharts	54	(3)
3.5.1 Guards	54	(2)
3.5.2 Target of Actions	56	(1)
3.5.3 Actual Parameter Values	56	(1)
3.5.4 Change Events	57	(1)
3.5.5 Restrictions on States	57	(1)
3.6 Completing Activity Diagrams	57	(2)
3.7 Completing Component Diagrams	59	(1)
3.8 Completing Use Cases	59	(2)
3.8.1 Preconditions and Postconditions	59	(2)
3.9 Modeling Styles	61	(4)
3.9.1 Definitions of Attributes or Operations	61	(1)
3.9.2 The Subset Constraint	62	(1)
3.9.3 Adding Inheritance Versus Invariants	63	(2)
3.10 Tips and Hints	65	(5)
3.10.1 Avoid Complex Navigation Expressions	65	(1)
3.10.2 Choose Context Wisely	66	(1)
3.10.3 Avoid allInstances	67	(1)
3.10.4 Split and Constraints	68	(1)
3.10.5 Use the collect Shorthand	69	(1)
3.10.6 Always Name Association Ends	69	(1)
3.11 Summary	70	(1)
Chapter 4 Implementing OCL	71	(22)
4.1 Implementation Process	71	(1)
4.2 Implementing UML Model Elements	72	(2)
4.3 Implementing the OCL Standard Library	74	(8)
4.3.1 OCL Basic Types	74	(3)
4.3.2 OCL Tuples	77	(1)
4.3.3 OCL Collection Types	77	(5)
4.4 Implementing OCL Expressions	82	(3)
4.4.1 Evaluation Order	82	(1)
4.4.2 No Side Effects	83	(1)
4.4.3 Getting Attribute and AssociationEnd Values	83	(1)
4.4.4 Let Expressions	84	(1)
4.4.5 Treating Instances as Collections	84	(1)
4.5 Merging Code Fragments	85	(5)
4.5.1 Derivation Rules	85	(1)
4.5.2 Invariants	86	(1)
4.5.3 Preconditions and Postconditions	86	(1)
4.5.4 Guards and Change Events in Statecharts	87	(2)
4.5.5 Code for Interaction Diagrams	89	(1)
4.6 Considerations for Constraints	90	(1)
4.6.1 When to Check Constraints	90	(1)
4.6.2 What to Do When a Constraint Fails	91	(1)
4.7 Summary	91	(2)
Chapter 5 Using OCL for MDA	93	(12)
5.1 Relation of OCL to MDA	93	(1)
5.2 Metamodels	93	(3)
5.3 The OCL and UML Metamodels	96	(3)
5.3.1 The UML Metamodel	96	(1)
5.3.2 The OCL Metamodel	97	(1)
5.3.3 The Relationship Between the UML and OCL Metamodels	98	(1)
5.4 Using OCL to Define Languages	99	(1)
5.5 Using OCL to Define Transformations	100	(3)
5.5.1 Example Transformation Definition	101	(2)
5.6 Summary	103	(2)
Part 2 Reference Manual	105	(66)
Chapter 6 The Context of OCL Expressions	107	(14)
6.1 A Combined Model	107	(3)
6.1.1 The Context of an OCL Expression	108	(1)
6.1.2 The self Keyword	109	(1)
6.1.3 More Than One Expression to a Context	109	(1)
6.2 Classes and Other Types	110	(1)
6.2.1 Invariants	110	(1)
6.2.2 Definitions of Attributes or Operations	111	(1)
6.3 Attributes and Association Ends	111	(1)
6.3.1 Derivation Rules	111	(1)
6.3.2 Initial Values	112	(1)
6.4 Operations	112	(2)
6.4.1 Preconditions and Postconditions	113	(1)
6.4.2 Body of Query Operations	113	(1)
6.5 Expressions in Behavior Diagrams	114	(2)
6.5.1 Instances	114	(1)
6.5.2 Conditions	114	(1)
6.5.3 Guards	114	(1)
6.5.4 Actual Parameter Values	114	(1)
6.5.5 Target to Actions or Activities	115	(1)
6.5.6 Change Events	115	(1)
6.6 Use Cases	116	(1)
6.6.1 Preconditions and Postconditions	116	(1)
6.7 Constraints and Inheritance	116	(5)
6.7.1 Consequences for Invariants	117	(1)
6.7.2 Consequences for Preconditions and Postconditions	118	(3)
Chapter 7 Basic OCL Elements	121	(8)
7.1 Expressions, Types, and Values	121	(1)
7.1.1 Value Types and Object Types	122	(1)
7.2 Basic Types and Operators	122	(4)
7.2.1 The Boolean Type	122	(2)
7.2.2 The Integer and Real Types	124	(2)
7.2.3 The String Type	126	(1)
7.3 Precedence Rules	126	(1)
7.4 Use of Infix Operators	127	(1)
7.5 Comments	127	(2)
Chapter 8 User-defined Types	129	(8)
8.1 Features of User-defined Types	129	(1)
8.1.1 Attributes and Operations	129	(1)
8.1.2 Class Operations and Attributes	130	(1)
8.2 Associations and Aggregations	130	(4)
8.2.1 Association Classes	132	(1)
8.2.2 Qualified Associations	133	(1)
8.3 Enumeration Types	134	(3)
Chapter 9 Collection Types	137	(18)
9.1 The Collection Types	137	(3)
9.1.1 Collection Constants	138	(1)
9.1.2 Collection Type Expressions	138	(1)
9.1.3 Collections Operations	139	(1)
9.1.4 Treating Instances as Collections	139	(1)
9.1.5 Collections of Collections	140	(1)
9.2 Operations on Collection Types	140	(6)
9.2.1 Operations with Variant Meaning	140	(5)
9.2.2 Operations on OrderedSets and Sequences Only	145	(1)
9.3 Loop Operations or Iterators	146	(9)
9.3.1 Iterator Variables	146	(2)
9.3.2 The isUnique Operation	148	(1)
9.3.3 The sortedBy Operation	148	(1)
9.3.4 The select Operation	149	(1)
9.3.5 The reject Operation	149	(1)
9.3.6 The any Operation	150	(1)
9.3.7 The for All Operation	150	(1)
9.3.8 The exists Operation	151	(1)
9.3.9 The one Operation	151	(1)
9.3.10 The collect Operation	152	(1)
9.3.11 Shorthand Notation for collect	152	(1)
9.3.12 The collectNested Operation	153	(1)
9.3.1 The Iterate Operation	153	(2)
Chapter 10 Advanced Constructs	155	(20)
10.1 Constructs for Postconditions	155	(3)
10.1.1 The @pre Keyword	155	(1)
10.1.2 The result Keyword	156	(1)
10.1.3 The ocllsNew Operation	156	(1)
10.1.4 The isSent Operator	156	(1)
10.1.5 The message Operator	157	(1)
10.2 Operations of the OclMessage Type	158	(2)
10.2.1 The hasReturned and result Operations	158	(1)
10.2.2 The isSignalCall and isOperationCall operations	159	(1)
10.3 Packaging Expressions	160	(1)
10.4 Local Variables	161	(1)
10.5 Tuples and Tuple Types	162	(1)
10.6 Undefined Values, the OclVoidType	163	(1)
10.7 Retyping or Casting	164	(1)
10.8 Type Conformance Rules	164	(1)
10.9 Accessing Overriden Features	165	(1)
10.10 The OclAny Type	166	(16)
10.10.1 Operations on OclAny	166	(3)
10.10.2 The allInstances Operation	169	(2)
Appendix A Glossary	171	(4)
Appendix B OCL Grammar Rules	175	(6)
B.1 EBNF Rules for Context Declaration	175	(1)
B.2 EBNF Rules for Expression	176	(5)
Appendix C A Business Modeling Syntax for OCL	181	(10)
C.1 Introduction	181	(1)
C.2 Informal Definition	182	(6)
C.2.1 Iterators	182	(4)
C.2.2 Collection Operations	186	(2)
C.2.3 Other Differences	188	(1)
C.3 Some Remarks on the Resemblance to SQL	188	(1)
C.4 More Elaborate Examples	189	(2)
Appendix D Example Implementation	191	(6)
Appendix E Differences Between OCL Versions 1.1 and 2.0	197	(4)
E.1 Syntax Changes	197	(1)
E.1.1 Context Declaration	197	(1)
E.1.2 Enumerations and Class Attributes and Operations	197	(1)
E.1.3 Missing Rolenames and Using Association Classes	198	(1)
E.1.4 Operations	198	(1)
E.2 New Types	198	(1)
E.3 Extra Predefined Operations	198	(1)
E.4 New Options in Postconditions	199	(1)
E.5 Other Changes	199	(2)
Bibliography	201	(2)
Index	203

Excerpts

In November 1997, the Object Management Group (OMG) set a standard for object-oriented analysis and design facilities. The standard, known as the Unified Modeling Language (UML), includes model diagrams, their seman-tics, and an interchange format between CASE tools. Within UML, the Object Constraint Language (OCL) is the standard for specifying expressions that add vital information to object-oriented models and other object modeling artifacts. In UML version 1.1, this information was thought to be limited to con-straints, where a constraint is defined as a restriction on one or more values of (part of) an object-oriented model or system. In UML version 2 the under-standing is that there is far more additional information that should be included in a model than constraints alone. Defining queries, referencing values, or stating conditions and business rules in a model, is all done by writing expressions, i.e. these are all expressed in OCL. OCL has evolved from an expression language in the Syntropy method through a business modeling language used within IBM until it was included in UML in 1997. At that point in time it received its current name. This name is currently well established and therefore it is not expedient to change it to, for instance,Object Expression Language, although this name would currently be more appropriate. OCL has been used as an expression language for object-oriented model-ing during the last six years. Today, a large number of tools support the lan-guage. Since OCL was first conceived there have been many changes and additions to the language. Lately this has led to a new version of OCL, ver-sion 2.0, to accompany the new version of UML. OCL version 2.0 is formally defined in theObject Constraint Language SpecificationOCL2002. This book explains all features of this version of OCL. Recently, the OMG has launched an initiative called the Model Driven Architecture (MDA). The essence of the MDA approach is that models are the basis for software development. To be able to work with this architecture good, solid, consistent, and coherent models are a neccesity. Using the com-bination of UML and OCL you are able to build such models. In the many books that have been published on the subject of UML, its expression language has not received the attention it deserves. A first aim of this book is to fill this gap and to explain UML's expression language, which supports the task of modeling object-oriented software as much as the UML dia-grams. The second aim of this book is to introduce OCL version 2.0 to a wider audience. Not everyone is pleased with reading a formal standard, the informa-tion should be available in a more easy to read book. The last aim of this book is to explain why the use of OCL is essential to the application of MDA. Without OCL and the languages, transformations, etc. that are all enabled by OCL, application of MDA is bound to fail. WHO SHOULD READ THIS BOOK The book is meant to be a textbook and reference manual for practitioners of object technology who find a need for more precise modeling. This certainly includes persons that want to apply MDA principles. These people will want to use OCL in their analysis and design tasks, most probably within the context of UML but potentially with other graphical object modeling languages. This book assumes that you have general knowledge of object-oriented modeling, preferably UML. If you lack this knowledge, there are many books on UML that you can read first. HOW THIS BOOK SHOULD BE USED Part 1 of this book explains how OCL can be put to use. Anyone unfamiliar with OCL should read this part. An introduction to the Model Driven Architecture is given and the key role OCL plays in that framework is described. In this part OCL is explained in a relatively informal way