Michael Schrefl

Extending object-oriented systems with roles

In many class-based object-oriented systems the association between as 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 serveral independent roles. The problem is even more servere 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 an instance of every role type whose role it currently plays. In a natural way, the approach extends traditional object-oriented concepts, such as classification, object identity, specialization, inheritance, and polymorphism in a natural way. The practicability of the approach is demonstrated by an implementation in Smalltalk. Smalltalk was chosen because it is widely known, which is not true for any particular class-based object-oriented database programming language. Roles can be provided in Smalltalk by adding a few classes. There is no need to modify the semantics of Smalltalk itself. Role hierarchies are mapped transparently onto ordinary classes. The presented implementation can easily be ported to object-oriented database programming languages based on Smalltalk, such as Gemstones OPAL 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 an instance of every role type whose role in currently plays.

Object/behavior diagrams

A novel diagram technique is presented to depict the structure as well as the behavior of objects. One of its distinguishing characteristics is its strict adherence to the object-oriented paradigm. A first prototype of an editor for object/behavior diagrams has been developed and is running on SUN-workstations. To assist the user the editor provides hypertext style facilities for navigating through different diagrams. For example, by clicking on an activity in a life cycle diagram one moves to the activity specification diagram of that activity.<<ETX>>

Active data warehouses: complementing OLAP with analysis rules

Abstract Conventional data warehouses are passive. All tasks related to analysing data and making decisions must be carried out manually by analysts. Todays data warehouse and OLAP systems offer little support to automatize decision tasks that occur frequently and for which well-established decision procedures are available. Such a functionality can be provided by extending the conventional data warehouse architecture with analysis rules , which mimic the work of an analyst during decision making. Analysis rules extend the basic event/condition/action (ECA) rule structure with mechanisms to analyse data multidimensionally and to make decisions. The resulting architecture is called active data warehouse .

Object class definition by generalization using upward inheritance

The authors show how the process of object class definition by generalization can be incorporated into object-oriented systems. Traditional message handling, which is mainly based on downward property inheritance, is revised and extended to upward property inheritance, so that a maximum of reusability of code and data can be achieved. Different types of semantic relationships that may hold between a generalization classs subclasses and their attributes are identified. The different semantic relationships can then be utilized to produce different default treatments of messages and upward property propagation.

Using an object-oriented approach to model multimedia data

Abstract Special requirements are identified that arise in the handling of multimedia data. Individual objects, e.g. documents, should be extendable beyond their types. Data dispersed over several databases must be integrated and handled uniformly. A clear distinction is to be drawn between the (internal) modelling and the (external) presentation of multimedia objects. Data model constructs should be provided to define various semantic relationships, such as roles, copies, and versions. A reference architecture for multimedia databases is introduced and the requirements are associated with the different components of this architecture. It is shown how object-oriented data models can be used and extended to meet the requirements set out above. In particular, the metaclass concept is proposed to provide at the meta level those features of the data model that are needed to handle multimedia applications.

Analysis of business process integration in Web service context

The integration of Web services is a recent outgrowth of the Business Process integration field that will require powerful meta-schema matching mechanisms supported by higher level abstractions, such as UML meta-models. Currently, there are many XML-based workflow process specification languages (e.g. XPDL, BPEL) which can be used to define business processes in the Web services and Grid Computing world. However, with limited capability to describe the relationships (schemas or ontologies) between process objects, the dominant use of XML as a meta-data markup language makes the semantics of the processes ambiguous. OWL-S (Ontology Web Language for Services) exploits the semantic description power of OWL to build an ontology language for services. It therefore becomes a candidate for an inter lingua. In this paper, we propose an integration framework for business processes, which is applied to Web services defined in OWL-S.

USING AN OBJECT-ORIENTED DIAGRAM TECHNIQUE FOR THE DESIGN OF INFORMATION SYSTEMS

Abstract An object-oriented diagram technique is introduced for the design of information systems. Structural properties of objects are depicted in object diagrams. Dynamic properties are shown in behaviour diagrams. Object diagrams are based on semantic data model concepts. Behaviour diagrams are based on Petri nets and model the life cycles of objects through a set of states (places) and activities (transitions). The relationship between Object/Behaviour diagrams and Predicate/Transition nets is shown. The semantics of Object/Behaviour diagrams is formally defined through a mapping into Predicate/Transition nets.

How to compose an object-oriented business process model?

Faced with the intensive business process reengineering activities in many companies, it is not surprising that the issue of process modelling has become a central concern. This paper shows that object-oriented system development methods can be applied to the field of business process modelling, but that certain steps are needed in advance. For example, it is necessary to compose a goal-means hierarchy, to establish necessary activities and roles, and to determine the input and output for each activity. In this paper, we examine step by step how business processes can be modelled, which data are needed for each step and which result would be produced during each step.

Behavior based integration of composite business processes

Integration of autonomous object-oriented systems requires the integration of object structure and object behavior. Past research in the integration of autonomous object-oriented systems has so far mainly addressed integration of object structure. During our research we have identified business process correspondences and have given proper integration operators. So far these integration operators are suited for creating generalized models but not for creating or dealing with the composition of business processes. In this paper we propose integration operators which are able to create, deal, and finalize composition between them. For modeling purposes we use the Unified Modeling Language (UML), especially activity diagrams.

Semantics of object-oriented data models — The evolving algebra approach

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 object-oriented 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).