Object-Oriented Technology

222 Pages·2015·2.082 MB·English

by  Suad Alagić (auth.)

Suad Alagić
Object-
Oriented
Technology
Object-Oriented Technology

Suad Alagic´
Object-Oriented Technology
123
SuadAlagic´
ComputerScienceProfessor
Portland,Maine,USA
Publications:http://dblp.uni-trier.de/pers/hd/a/Alagic:Suad
Website:https://sites.google.com/site/suadalagicme/
ISBN978-3-319-20441-3 ISBN978-3-319-20442-0 (eBook)
DOI10.1007/978-3-319-20442-0
LibraryofCongressControlNumber:2015944088
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Adrian,Evan,Lucas,andDario

Preface
Thecoreideaofthisbookisthatobject-orientedtechnologyisagenerictechnology
whose various technical aspects could be presented in a unified and consistent
framework. This applies to both practical and formal aspects of object-oriented
technology.
The approach in the book is based on typed technologies. The core notions
fit mainstream object-oriented languages such as Java and C#. However, perhaps
the most distinctive feature of this book is that it is based on object-oriented con-
straints(assertions),theirspecificationandverification.Object-orientedconstraints
apply to specification and verification of object-oriented programs, specifica-
tion of the object-oriented virtual platform, more advanced concurrent models,
database integrity constraints, and object-oriented transactions, their specification
andverification.
In Chap.1, we define the key notions of typed object-oriented technology: the
notions of types, objects, classes, messages, and methods. This is followed by the
notions of inheritance and subtyping and their formal and pragmatic properties.
Staticanddynamicbindingasitappliestomessagesandmethodsisthendiscussed.
Parametrictypesareessentialformoderntypedobject-orientedtechnologies.They
are given due attention through a detailed analysis of various issues related to
parametrictypes.
A distinctive view in this book is that types are preferably equipped with
assertions.AssertionsarethetopicofChap.2.Thischapterfirstspecifiesthebasic
reasoningrulessuchasthosethatapplytoassignments,conditionalstatements,and
loops.Loopinvariantsandaverificationtechniqueforprovingterminationarethen
discussed. Object-oriented assertions: method preconditions and postconditions,
and class invariants are discussed in detail. Finally, we revisit the notion of
subtypinginthepresenceofassertionsandexplaintheallimportantcompatibility
requirementsforclassescalledbehavioralsubtyping.Thischapteralsoshowshow
assertions are specified in a sample application that makes use of a practical
assertionspecificationandverificationtool.
The formal basis in this book for types and constraints had an impact on the
notation used to present code samples that are based on Java, C#, assertion, and
vii
viii Preface
data languages. Although these code samples are close to the source languages,
they are more conceptual and based on notation that is closer to the standard
mathematicalnotation.Thisproducesaconsistentframeworkforbothcodesamples
and their formal aspects expressed by constraints. The correspondence with the
sourcenotationisimmediate.
In Chap.3, we describe a modern environment that supports typed object-
oriented technology. The components of this environment include reflection, the
actualobject-orientedvirtualmachine,andsupportforpersistentobjects.Reflection
is presented following the initial Java specifications that are more suitable for
explanationofcoreconceptsunlikethemorerecentrevisions.Moderntypedobject-
oriented languages such as Java or C# run on an object-oriented virtual machine.
Our presentation is an abstraction of the existing very low-level specifications
of object-oriented virtual machines. A distinctive feature of the presentation is
the use of assertions to define the semantics of the basic operations. An object-
orientedplatformshouldsupportpersistentobjects,i.e.,objectswithlonglifetimes.
This chapter also presents persistent models and mechanisms such as orthogonal
persistenceandserializability.
In Chap.1, we present the basic rules of object-oriented type systems in a
mostly informal manner. However, type systems have an elaborate formal theory.
In Chap. 4, we show how some of the elements of type theory apply to an
object-oriented programming language. We first explain the basic typing rules for
statementssuchasassignment,conditionals,andloops,aswellasforexpressions.
Then we focus on the rules of object-oriented type systems that govern classes,
inheritance, subtyping, and messages. These static typing rules are followed by
dynamic type checking rules that mainstream object-oriented languages have, and
the formal rules for parametric types. In addition, we present static and dynamic
typing rules that apply to reflection. Finally, we show what kind of problems
violation of type safe rules can cause. We take a well-known paradigm of type
erasurethatwasthebasisofthetechniqueforextendingJavawithparametrictypes.
This paradigm is provably incorrect as demonstrated by a variety of cases of type
violationpresentedinthischapter.
Concurrentobject-orientedmodelsarediscussedinChap.5.Wefirstpresentthe
modelofconcurrentthreadsofexecution.Then,weexplainthebasicmechanisms
forsynchronizingconcurrentaccessofmultiplethreadstoobjectsonthecommon
heap. We discuss the relationship between synchronization and inheritance, and
the relationship between serialization and synchronization. We demonstrate what
the implications are of synchronized versus unsynchronized executions. Then, we
introduceamoregeneralconcurrentanddistributedmodelbasedonasynchronous
messages. The basis of this model is the fact that messages may be viewed as
objects.Inthisnewframework,itisnaturaltodefineformallytherulesofbehavioral
subtyping.Finally,weintroduceaverygeneralmodelofconcurrentactiveobjects,
eachequippedwithitsownvirtualmachine.Ambientsofsuchobjectsarediscussed
aswell.
Object-oriented database technology (the topic of Chap.6) addresses the lim-
itations of relational and extended relational technologies in managing complex
Preface ix
objects that exhibit complex behavior. Object-oriented database technology is
also addressing the problem of the mismatch between the dominating software
technology,whichisobject-oriented,andthedominatingdatabasetechnologythat
is relational, or object-relational at best. This specifically applies to the so-called
“impedancemismatch”betweendataandprogramminglanguages.Wefirstdiscuss
thebasicfeaturesofobject-orienteddefinitionandquerylanguages.Welookatthe
mostimportantobject-orienteddatabasetechnologies.Weexplainthecorefeatures
ofthosetechnologiesthatincludedatabasecollectionclasses,interfacingdatabases
from an object-oriented programming language, and object-oriented transactions.
We also revisit the typing issues for persistent collections. The core features of a
specific current technology and its application are presented as well. Finally, we
discuss a critical limitation of all object-oriented and other database technologies:
inability to specify and enforce very general database integrity constraints. We
presentanobject-orienteddatabaseparadigmbasedonsuchgeneralconstraints.
In Chap.7, we show how two critical formal notions in this book: types
and constraints, apply to two significant practical problems. The first problem is
specification of database type systems in a formal manner. The second problem
is specification and verification of object-oriented transactions. Database systems
are typically not based on a formally specified type system. This leads to non-
trivial problems that we demonstrate in this chapter. We consider a type system
required by object-oriented database systems and establish a collection of the
required formal rules showing the typing problems in object-oriented database
languages.Thischapteralsoaddressesanotherkeyfeatureofdatabasetechnologies:
transactions. Unlike other approaches, object-oriented schemas and transactions
are in our approach equipped with integrity constraints expressed in an object-
orientedassertionlanguage.Thisisfollowedbyobject-orientedconsistencyissues.
The presentation is based on a sample object-oriented schema equipped with very
generalintegrityconstraintsandsampletransactions.Therelationshipbetweenthe
integrity constraints and queries is discussed, as well as inheritance for object-
oriented schemas equipped with constraints. An essential issue of the role of
dynamicversusstaticcheckingofconstraintsisalsoaddressedinthischapter.
Portland,Maine,USA SuadAlagic´
Acknowledgements
The author is grateful to two software engineers, Russell Gillen and Thomas
Keschl, his former graduate students, for their numerous valuable comments that
significantlyimprovedthemanuscript.