In many class-based object-oriented systems the association between an instance and a class is exclusive and permanent. Therefore these systems have serious difficulties in representing objects taking on different roles over time. Such objects must be reclassified any time they evolve (e.g., if a person becomes a student and later an employee). Class hierarchies must be planned carefully and may grow exponentially if entities may take on several independent roles. The problem is even more severe for object-oriented databases than for common object-oriented programming. Databases store objects over longer periods, during which the represented entities evolve. This article shows how class-based object-oriented systems can be extended to handle evolving objects well. Class hierarchies are complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on. At any point in time, an entity is represented by an instance of the root and a...

The duality of objects and relationships is so deeply embedded in our thinking that almost all modelling languages include it as a fundamental distinction. Yet there is evidence that the two are naturally complemented by a third, equally fundamental notion: that of roles. Although definitions of the role concept abound in the literature, we maintain that only few are truly original, and that even fewer acknowledge the intrinsic role of roles as intermediaries between relationships and the objects that engage in them. After discussing the major families of role conceptualizations, we present our own basic definition and demonstrate how it naturally accounts for many modelling issues, including multiple and dynamic classification, object collaboration, polymorphism, and substitutability. <3 2000 Elsevier Science B.V. All rights reserved.

In a class hierarchy, a “role set ” is t,he set of classes where an object may reside simultaneously. A “migration pattern ” is a sequence of role sets. A “migration inventory, ” which is a set, of migrat,ion patterns, is viewed as a dynamic const,raintm on ohjrct migration. A set of transact ious is “sound ” wrt a11 inventory if it. generates only pat.t.t~rns in the invrntory; “complete ” if all pat,terns in the invent,ory can be generated. An initial stucly on characterizing migration inventories of transact,ions is presented. Three update languages are considered: SL which contains five operat,ors, CSL+ which ext rn(ls SL wit.h posit.ivc conditionals, and CSL which allows hot,h positive and negative condit.ionals. Four kinds of invent.orics are studied based on ln~znrss and znj~~,rtl~ntr s/art. It is shown that inventories produced by SL t,ransactions are regular and every regular inventory can be generated by SL transactions. Soundness and complet,eness for SL t,ransactions are decidahlt3. lnvc\llt,orics gpnrrated by CSL (CSL+) t,ra.nsactions arc r.e‘. and every r.e. inventory can be generat,rd by (:SL+ (CSL) transa.ctions under nonimmediate st,art,. It is also show t,hat, every r.e. immediate-start invent,ory can be obtained by a left quotient, of t,he invent,ory of CSL+ (CSL) transactions hy a regular seb. The exact, charact#erizat.ions are open. However, cvrry contrxl-frcr srt can be generat,ed. Soundness and rmllplPt~enms for ($1, (CSL+) t,ransa.ctions are undecidahlr. 1

In this paper, we argue that object-oriented models must be able to represent three kinds of taxonomic structures: static subclasses, dynamic subclasses and role classes. If CAR is a static subclass of V EHICLE, then a vehicle that is not a car can never migrate to the CAR subclass. If EMP loyee is a dynamic subclass of PERSON , then a PERSON that is not an employee may migrate to EMP . In both cases, an instance of the subclass is identical to an instance of the superclass. Finally, if EMP is modeled as a role class of PERSON every employee differs from every person, but a PERSON instance can acquire one or more EMP instances as roles. We outline an approach to formalizing these taxonomic structures in order-sorted dynamic logic with equality. Keywords: Theoretical foundations, formal methods, OO analysis and design February 2, 1994 Contents 1 Introduction 1 2 Methodological aspects of role-playing and class migration 1 2.1 Object classification and identification : : : : : : : : :...

Although the concept of roles is becoming a popular research issue in object-oriented databases and has been proven to be useful for dynamic and evolving applications, it has only been described conceptually in most of the previous work. Moreover, the important issues such as the semantics of roles (e.g., message passing) are seldom discussed. Furthermore, none of the previous work has investigated the idea of role player qualification, which models the fact that not every object is qualified to play a particular role. In this paper, we present a data model and the semantics of roles. We discuss each of the above issues and illustrate the ideas with examples. From these examples, we can easily see that the problems we discussed are fundamental and indeed exist in many complex applications. 1. Introduction In class-based object-oriented systems, real-world entities are represented as instances of the most specific class [3] in which they can be classified. However, when modeling applic...

The formal description of the semantics of object-oriented data models is still an open problem. Some characteristic features of object-oriented data models, such as methods and inheritance, involve investigating data and schema. Therefore they can not be handled straightforwardly with first order logic. As an alternative, we propose the evolving algebra approach to specify the formal semantics of objectoriented data models. Evolving algebras provide a framework for defining the operational semantics of programming languages based on dynamic structures. In this paper we show how evolving algebras can be used in particular to define the operational semantics of object creation, of overriding and dynamic binding, and of inheritance at the type level (type specialization) and at the instance level (object specialization).

In this paper we investigate several concepts that are known in database research for some time but which are still surrounded by some confusion. We start with the concepts of object identifier, surrogate and key and list the differences between these concepts, which in practice are often ignored. Sharpening these differences allows us to analyze the distinction between objects and roles that recently surfaced in the literature. Distinguishing objects from roles helps to avoid migration of objects between classes and thus the problems associated with it. We show that this distinction requires the use of role identifiers that, just as object identifiers, should be globally unique and unchangeable. We next show that using role identifiers requires a distinction between two essentially different kinds of inheritance relationships, is-a inheritance and played-by inheritance. These are often both treated as if they were one and the same kind of is-a relationship. The result of the discussio...

Object-oriented databases (OODBs) are believed to more naturally reflect the behavior and organization of complex application domains. The schema consists of a collection of classes, organized into hierarchies which nicely organize abstractions over the domain. Objects are created as instances of classes, encapsulating data and interpretation of data together. An important characteristic is the support for evolutionary programming, and so that existing programs may be extended with new classes without affecting other parts of the system.

Multiple inheritance is still a controversial feature in traditional object-oriented languages, as evidenced by its omission from such languages as Modula-3, Objective C and Java^TM. Nonetheless, users of such languages often complain about having to work around the absence of multiple inheritance. Automating delegation, in combination with a multiple subtyping mechanism, provides many of the same benefits as multiple inheritance, yet sidesteps most of the associated problems. This simple feature could satisfy both the designers and the users of class based object oriented languages. In this paper, we discuss why automated delegation is desirable. We also present Jamie, a freeware preprocessor-based extension to Java that offers such an alternative. Automated Delegation is a Viable Alternative to Multiple Inheritance in Class Based Languages John Viega Dept. Of Computer Science University Of Virginia Charlottesville, VA 22903 viega@list.org Bill Tutt Microsoft Corporat...

ADOME, ADvanced Object Modeling Environment, an approach to integrating data and knowledge management based on object-oriented technology, is presented. Next generation information systems will require more flexible data modelling capabilities than those provided by current object-oriented DBMSs. In particular, integration of data and knowledge management capabilities will become increasingly important. In this context, ADOME provides versatile role facilities that serve as "dynamic binders" between data objects and production rules, thereby facilitating flexible data and knowledge management integration. A prototype that implements this mechanism and the associated operators has been constructed on top of a commercial object-oriented DBMS and a rule base system. Index Terms: Object modeling, knowledge semantics, dynamic roles, object-oriented databases, nextgeneration information systems 1 Introduction Increasingly, organizations require more intelligent information management. In o...