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Software engineering: Object-oriented approach
239
Session C2:
SOFTWARE ENGINEERING: Object-Oriented Approach Chai rman:
Mike Papazoglou Gesellschaft fhr Mathernatik und Datenverarbeitung St. Augustin (F.R.G.)
Object oriented programming has quite rightly become.. the catchword of the 80's. There is a common denominator underlying the various directions aa~d tendencies in object orientation, namely, to better capture the semantics of applications and of the systems themselves and, thus, offer a much friendlier and creative environment for both end users and system developers. This in turn brings an easiness and clarity of programming style and results in upgraded productivity. Accordingly, the object oriented programming approach holds much promise as a framework for modern programming systems and environments, and it is not surprising that it encompasses various computer science disciplines including programming languages, operating systems, computer architectures, databases and knowledge bases. The objective of this session were to bring together representative papers which review current research in this area and explore the role of the object oriented approach in the design and realization of complex systems. The papers in this session collectively provide a snapshot of current research and trends in object-orientation and touch on many interesting research issues. In preparing this overview I discovered some interesting relations among the three first papers, such as the fact that they propose different kinds of object oriented systems-models to cope with the intricacies and peculiarities of the three diametrically different disciplines they stand for: application oriented software, database systems, and real time systems. Furthermore, the papers do not address one topic but touch on many arems at the same time. The paper by Krolak and Antipa deals with an application oriented software system that touches on information representation concepts. In the paper by Marines and Papazoglou the problems associated with query languages and object oriented structures become interwind with the problems of knowledge based management systems. Finally, in the paper by Plessmann and Tassakos the problems associated with object oriented systems and programming are related to real time processing, distributed and multiprocessor architectures.
Krolak and Antipa describe a system called DEOS (Dynamically Extensible Object Oriented System) that was developed to support a portfolio management system for brokerage applications. The system in addition to the objectoriented characteristics of inheritance, information hiding, etc, supports dynamic creation of new object classes from ASCII files. DEOS objects are of two varieties: instance objects and factory objects. Instance objects are created by the user by messaging the factory objects and their purpose is to hold user's data. Factory objects contain information for a class of objects and can be either compiled and linked as complete objects or can be dynamically built at run time. The compiled factory objects form the superclass of all objects in the system. The paper by Marines and Papazoglou discusses the main operational requirements for an enhanced object oriented data model capable of capturing the semantics of global modeling in a heterogeneous distrilmted database system. The purpose of such a data model is to express the structure and semantics of diverse data models and to support a smooth development of families of procedural and non procedural data languages. Examples are appended to indicate how this can be achieved in the case of relational and functional data models. Plessmann and Tassakos point out the inadequacies of contemporary object oriented systems to cope with the problems of real-time processing systems and propose their own system. Their approach intents to introduce the benefits of object oriented systems in the design and realization of parallel and distributed real-time systems. This approach is combining object oriented concepts with some concurrent processing primitives. Furthermore, they defines a handful of communication primitives upon which message passing is based. In this systmn message passing mechanisms can be both synchronous and asynchronous.
240
Session C2: Software Engineering
The final paper by Christodoulakis elaborates on an interesting concept, namely on how to describe the semantics of object oriented languages using a special Petri-net dialect called Predicate/Transition (PrT) nets. As a vehicle for this research he chose the well known object oriented language Smalltalk. The paper shows that instance vari-
ables in Smalltalk can be represented as places while a set of transitions corresponds to methods in a class. The paper provides a series of examples as to how the concepts of hierarchies, inheritance, etc, would look like if they were to be implemented as PrT nets.
Session C2:
SOFTWARE ENGINEERING: Object-Oriented Approach Chai rman:
Mike Papazoglou Gesellschaft fhr Mathernatik und Datenverarbeitung St. Augustin (F.R.G.)
Object oriented programming has quite rightly become.. the catchword of the 80's. There is a common denominator underlying the various directions aa~d tendencies in object orientation, namely, to better capture the semantics of applications and of the systems themselves and, thus, offer a much friendlier and creative environment for both end users and system developers. This in turn brings an easiness and clarity of programming style and results in upgraded productivity. Accordingly, the object oriented programming approach holds much promise as a framework for modern programming systems and environments, and it is not surprising that it encompasses various computer science disciplines including programming languages, operating systems, computer architectures, databases and knowledge bases. The objective of this session were to bring together representative papers which review current research in this area and explore the role of the object oriented approach in the design and realization of complex systems. The papers in this session collectively provide a snapshot of current research and trends in object-orientation and touch on many interesting research issues. In preparing this overview I discovered some interesting relations among the three first papers, such as the fact that they propose different kinds of object oriented systems-models to cope with the intricacies and peculiarities of the three diametrically different disciplines they stand for: application oriented software, database systems, and real time systems. Furthermore, the papers do not address one topic but touch on many arems at the same time. The paper by Krolak and Antipa deals with an application oriented software system that touches on information representation concepts. In the paper by Marines and Papazoglou the problems associated with query languages and object oriented structures become interwind with the problems of knowledge based management systems. Finally, in the paper by Plessmann and Tassakos the problems associated with object oriented systems and programming are related to real time processing, distributed and multiprocessor architectures.
Krolak and Antipa describe a system called DEOS (Dynamically Extensible Object Oriented System) that was developed to support a portfolio management system for brokerage applications. The system in addition to the objectoriented characteristics of inheritance, information hiding, etc, supports dynamic creation of new object classes from ASCII files. DEOS objects are of two varieties: instance objects and factory objects. Instance objects are created by the user by messaging the factory objects and their purpose is to hold user's data. Factory objects contain information for a class of objects and can be either compiled and linked as complete objects or can be dynamically built at run time. The compiled factory objects form the superclass of all objects in the system. The paper by Marines and Papazoglou discusses the main operational requirements for an enhanced object oriented data model capable of capturing the semantics of global modeling in a heterogeneous distrilmted database system. The purpose of such a data model is to express the structure and semantics of diverse data models and to support a smooth development of families of procedural and non procedural data languages. Examples are appended to indicate how this can be achieved in the case of relational and functional data models. Plessmann and Tassakos point out the inadequacies of contemporary object oriented systems to cope with the problems of real-time processing systems and propose their own system. Their approach intents to introduce the benefits of object oriented systems in the design and realization of parallel and distributed real-time systems. This approach is combining object oriented concepts with some concurrent processing primitives. Furthermore, they defines a handful of communication primitives upon which message passing is based. In this systmn message passing mechanisms can be both synchronous and asynchronous.
240
Session C2: Software Engineering
The final paper by Christodoulakis elaborates on an interesting concept, namely on how to describe the semantics of object oriented languages using a special Petri-net dialect called Predicate/Transition (PrT) nets. As a vehicle for this research he chose the well known object oriented language Smalltalk. The paper shows that instance vari-
ables in Smalltalk can be represented as places while a set of transitions corresponds to methods in a class. The paper provides a series of examples as to how the concepts of hierarchies, inheritance, etc, would look like if they were to be implemented as PrT nets.