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Papers by Michael Schrefl

Data & Knowledge Engineering, 2001

Data warehouses, which are the core elements of On-Line Analytical Processing (OLAP) systems, are... more Data warehouses, which are the core elements of On-Line Analytical Processing (OLAP) systems, are passive since all tasks related to analyzing and making decisions must be carried out manually. This paper introduces a novel architecture, the active data warehouse, which applies the idea of event-condition-action rules (ECA rules) from active database systems to automize repetitive analysis and decision tasks in data warehouses. The work of an analyst is mimicked by analysis rules, which extend the capabilities of conventional ECA rules in order to support multidimensional analysis and decision making.

Software - Practice and Experience, 2002

Active data warehouses belong to a new category of decision support systems, which automate decis... more Active data warehouses belong to a new category of decision support systems, which automate decision making for routine decision tasks and semi-routine decision tasks. Just as active database systems extend conventional database systems with event–condition–action rules for integrity constraint enforcement or procedure execution, active data warehouses extend conventional data warehouses with analysis rules that mimic the work of an analyst during decision making. This paper demonstrates how analysis rules can be implemented on top of a passive relational data warehouse system by using commercially available database technology. Copyright © 2002 John Wiley & Sons, Ltd.

ABSTRACT Inheritance is one of the most prominent features of object-oriented design. Object type... more ABSTRACT Inheritance is one of the most prominent features of object-oriented design. Object types are organized in hierarchies in which subtypes inherit the structure as well as the behavior of supertypes. As inheritance of behavior is concerned, the discussion has mainly focused on inheritance of single activities in the past. Object behavior, however, is specified at two interrelated levels of detail: at the activity level and at the object type level. The latter is specified in terms of object life cycles that identify legal sequences of states and activities. In this paper we treat inheritance of object life cycles in the realm of Behavior Diagrams, which are based on Petri nets. A behavior diagram of an object type models the possible life cycles of its instances by states, activities, and arcs corresponding to places, transitions, and arcs of Petri nets. In an inheritance hierarchy, subtypes usually specialize supertypes in two ways: by extension and by refinement. For Behavior Diagrams,...

Many organizations provide access to their workflows via Web interfaces, giving customers the opp... more Many organizations provide access to their workflows via Web interfaces, giving customers the opportunity to create and manipulate business cases interactively according to a predefined set of operations. Since enterprises can request such Web services in order to satisfy their business goals, it may be desirable for these enterprises to access Web services not only interactively, but to import and integrate them into their own workflow management systems and to invoke them from within workflow applications. There are several initiatives to standardize the specification of services in order to provide them to enterprises for import. Yet currently most providers of Web services do not support these specifications. Thus, requesting enterprises must extract the workflows and business objects behind the provided Web interface from the visible Web pages. This paper presents a design architecture for extracting the Web interface and the underlying workflows and business objects from a Web site in consecutive extraction phases, each phase resulting in a conceptual schema at one particular level in the architecture. The architecture satisfies service independence, i.e., changes in the Web interface do not require a complete redesign of the conceptual schemas, and level-specific integration, i.e., extracted Web services can be integrated at different design levels depending on the purpose of integration

Page 1. Ob ject/Behavior Diagrams Gerti Kappel Department of Statistics and Computer Science Univ... more Page 1. Ob ject/Behavior Diagrams Gerti Kappel Department of Statistics and Computer Science University of Vienna, Austria Abstract Schema diagrams are widely used in database design as they support a high-level graphical ...

ABSTRACT Object-oriented data models organize objects according to common properties into classes... more ABSTRACT Object-oriented data models organize objects according to common properties into classes. Similarly, some object -oriented systems organize classes into metaclasses which define common properties of their class instances. But in none of them metaclasses can be used to define common properties of instances of their instances. Metaclasses in VODAK, a distributed object-oriented database system developed at IPSI, have been extended in that direction. They can be employed to predefine a common structure and behavior of classes and of individual objects at the metaclass level. Using this feature, metaclasses can be employed to introduce new data model primitives, and thus, to extend the VODAK kernel model with capabilities needed in specific application domains. We illustrate the use of metaclasses in database integration. A frequent approach to integrate a set of related classes is to define a generalization class for them. Class definition by generalization, however, is usually not suppor...

Workflow transparency refers to the ability of considering a business process independently of th... more Workflow transparency refers to the ability of considering a business process independently of the workflow implementing it. Unlike current workflow systems, which do not differentiate between business processes and workflows, workflow transparency requires to model business processes and workflows separately. Workflow systems supporting workflow transparency offer advantages comparable with database systems supporting data independence. Similarly as data independence allows to change the actual organization of data without effecting applications accessing the database at the conceptual level, workflow transparency allows for dynamic re-organisation of the actual flow of work without effecting the overall results of business processes.

In this paper we introduce the concept of cooperative message handling, in whichseveral objects a... more In this paper we introduce the concept of cooperative message handling, in whichseveral objects act together in answering a message they have received jointly. Cooperativemessage handling extends the traditional message passing paradigm whichrequires the receiver of a message to be a single object only. Cooperative messagesare defined with cooperation contracts which are established between several objecttypes. A cooperative message is

The formal description of the semantics of object-oriented data models is still an open problem. ... more 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).

Data & Knowledge Engineering, 2001

Database schemas are often not defined by a single person but by several futureusers of the datab... more Database schemas are often not defined by a single person but by several futureusers of the database who define their possibly different views on the proposeddatabase schema. These views are collected and integrated during the subsequentdesign step of view integration. In object-oriented databases, view integration musthandle the integration of the structure and the behavior of objects. Whereas integrationof object structure

ACM Transactions on Information Systems, 1996

This paper discusses the resolution of structural differences in the framework of object-oriented... more This paper discusses the resolution of structural differences in the framework of object-oriented systems. Two main concepts are introduced: message forwarding and context coloring. Message forwarding comes in if some object can not answer a message by itself because of ...

1072 p. Funkhäuser et al. To operate the databases after a merger of the two companies jointly th... more 1072 p. Funkhäuser et al. To operate the databases after a merger of the two companies jointly the differences in attributes and methods will become burdensome. A view offering a single set of data manipulation functions (mes-sages) should be available. This is achieved by the ...

Computer Communications, 1990

Special requirements are identified that arise in the handling of multimedia data. Individual obj... more Special requirements are identified that arise in the handling of multimedia data. Individual objects, eg 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 ...

Data & Knowledge Engineering, 2001

Data warehouses, which are the core elements of On-Line Analytical Processing (OLAP) systems, are... more Data warehouses, which are the core elements of On-Line Analytical Processing (OLAP) systems, are passive since all tasks related to analyzing and making decisions must be carried out manually. This paper introduces a novel architecture, the active data warehouse, which applies the idea of event-condition-action rules (ECA rules) from active database systems to automize repetitive analysis and decision tasks in data warehouses. The work of an analyst is mimicked by analysis rules, which extend the capabilities of conventional ECA rules in order to support multidimensional analysis and decision making.

Software - Practice and Experience, 2002

Active data warehouses belong to a new category of decision support systems, which automate decis... more Active data warehouses belong to a new category of decision support systems, which automate decision making for routine decision tasks and semi-routine decision tasks. Just as active database systems extend conventional database systems with event–condition–action rules for integrity constraint enforcement or procedure execution, active data warehouses extend conventional data warehouses with analysis rules that mimic the work of an analyst during decision making. This paper demonstrates how analysis rules can be implemented on top of a passive relational data warehouse system by using commercially available database technology. Copyright © 2002 John Wiley & Sons, Ltd.

ABSTRACT Inheritance is one of the most prominent features of object-oriented design. Object type... more ABSTRACT Inheritance is one of the most prominent features of object-oriented design. Object types are organized in hierarchies in which subtypes inherit the structure as well as the behavior of supertypes. As inheritance of behavior is concerned, the discussion has mainly focused on inheritance of single activities in the past. Object behavior, however, is specified at two interrelated levels of detail: at the activity level and at the object type level. The latter is specified in terms of object life cycles that identify legal sequences of states and activities. In this paper we treat inheritance of object life cycles in the realm of Behavior Diagrams, which are based on Petri nets. A behavior diagram of an object type models the possible life cycles of its instances by states, activities, and arcs corresponding to places, transitions, and arcs of Petri nets. In an inheritance hierarchy, subtypes usually specialize supertypes in two ways: by extension and by refinement. For Behavior Diagrams,...

Many organizations provide access to their workflows via Web interfaces, giving customers the opp... more Many organizations provide access to their workflows via Web interfaces, giving customers the opportunity to create and manipulate business cases interactively according to a predefined set of operations. Since enterprises can request such Web services in order to satisfy their business goals, it may be desirable for these enterprises to access Web services not only interactively, but to import and integrate them into their own workflow management systems and to invoke them from within workflow applications. There are several initiatives to standardize the specification of services in order to provide them to enterprises for import. Yet currently most providers of Web services do not support these specifications. Thus, requesting enterprises must extract the workflows and business objects behind the provided Web interface from the visible Web pages. This paper presents a design architecture for extracting the Web interface and the underlying workflows and business objects from a Web site in consecutive extraction phases, each phase resulting in a conceptual schema at one particular level in the architecture. The architecture satisfies service independence, i.e., changes in the Web interface do not require a complete redesign of the conceptual schemas, and level-specific integration, i.e., extracted Web services can be integrated at different design levels depending on the purpose of integration

Page 1. Ob ject/Behavior Diagrams Gerti Kappel Department of Statistics and Computer Science Univ... more Page 1. Ob ject/Behavior Diagrams Gerti Kappel Department of Statistics and Computer Science University of Vienna, Austria Abstract Schema diagrams are widely used in database design as they support a high-level graphical ...

ABSTRACT Object-oriented data models organize objects according to common properties into classes... more ABSTRACT Object-oriented data models organize objects according to common properties into classes. Similarly, some object -oriented systems organize classes into metaclasses which define common properties of their class instances. But in none of them metaclasses can be used to define common properties of instances of their instances. Metaclasses in VODAK, a distributed object-oriented database system developed at IPSI, have been extended in that direction. They can be employed to predefine a common structure and behavior of classes and of individual objects at the metaclass level. Using this feature, metaclasses can be employed to introduce new data model primitives, and thus, to extend the VODAK kernel model with capabilities needed in specific application domains. We illustrate the use of metaclasses in database integration. A frequent approach to integrate a set of related classes is to define a generalization class for them. Class definition by generalization, however, is usually not suppor...

Workflow transparency refers to the ability of considering a business process independently of th... more Workflow transparency refers to the ability of considering a business process independently of the workflow implementing it. Unlike current workflow systems, which do not differentiate between business processes and workflows, workflow transparency requires to model business processes and workflows separately. Workflow systems supporting workflow transparency offer advantages comparable with database systems supporting data independence. Similarly as data independence allows to change the actual organization of data without effecting applications accessing the database at the conceptual level, workflow transparency allows for dynamic re-organisation of the actual flow of work without effecting the overall results of business processes.

In this paper we introduce the concept of cooperative message handling, in whichseveral objects a... more In this paper we introduce the concept of cooperative message handling, in whichseveral objects act together in answering a message they have received jointly. Cooperativemessage handling extends the traditional message passing paradigm whichrequires the receiver of a message to be a single object only. Cooperative messagesare defined with cooperation contracts which are established between several objecttypes. A cooperative message is

The formal description of the semantics of object-oriented data models is still an open problem. ... more 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).

Data & Knowledge Engineering, 2001

Database schemas are often not defined by a single person but by several futureusers of the datab... more Database schemas are often not defined by a single person but by several futureusers of the database who define their possibly different views on the proposeddatabase schema. These views are collected and integrated during the subsequentdesign step of view integration. In object-oriented databases, view integration musthandle the integration of the structure and the behavior of objects. Whereas integrationof object structure

ACM Transactions on Information Systems, 1996

This paper discusses the resolution of structural differences in the framework of object-oriented... more This paper discusses the resolution of structural differences in the framework of object-oriented systems. Two main concepts are introduced: message forwarding and context coloring. Message forwarding comes in if some object can not answer a message by itself because of ...

1072 p. Funkhäuser et al. To operate the databases after a merger of the two companies jointly th... more 1072 p. Funkhäuser et al. To operate the databases after a merger of the two companies jointly the differences in attributes and methods will become burdensome. A view offering a single set of data manipulation functions (mes-sages) should be available. This is achieved by the ...

Computer Communications, 1990

Special requirements are identified that arise in the handling of multimedia data. Individual obj... more Special requirements are identified that arise in the handling of multimedia data. Individual objects, eg 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 ...