Hans-Dieter Ehrich

Conceptual modelling of database applications using an extended ER model

Abstract In this paper, we motivate and present a data model for conceptual design of structural and behavioural aspects of databases. We follow an object centered design paradigm in the spirit of semantic data models. The specification of structural aspects is divided into modelling of object structures and modelling of data types used for describing object properties. The specification of object structures is based on an E xtended E ntity- R elationship (EER) model. The specification of behavioural aspects is divided into the modelling of admissible database state evolutions by means of temporal integrity constraints and the formulation of database (trans)actions. The central link for integrating these design components is a descriptive logic-based query language for the EER model. The logic part of this language is the basis for static constraints and descriptive action specifications by means of pre- and postconditions. A temporal extension of this logic is the specification language for temporal integrity constraints. We emphasize that the various aspects of a database application are specified using several appropriate, but yet compatible formalisms, which are integrated by a unifying common semantic.

Abstract Object Types: A Temporal Perspective

The notion of abstract object type (AOT) tends to overlay the already classical concept of abstract data type (ADT) in several fields of application. Objects, although much more complex than data, have the advantage of dealing with states and processes. For that reason, they become useful, for instance, in the design of database applications and in software engineering. The difficulty lies in finding a suitable formalism for the abstract definition of objects, at least as effective as the equational formalism has been in the definition of abstract data types. The purpose of this paper is to present and discuss the main features of such a formalism. Concepts, tools and techniques are provided for the abstract definition of objects. A primitive language is presented allowing structured and rather independent definitions of object types. Each object is described as a temporal entity that evolves because of the events that happen during its life. The interaction between objects is reduced to event sharing. Both liveness and safety requirements can be stated and verified. Two case studies are presented for illustrating every aspect of the approach: the stack example which is very popular in the ADT area, thus allowing the comparison between the concepts of ADT and AOT, and the well known example of the eating philosophers which allows the discussion of the dynamic aspects.

Algebraic and operational semantics of specifications allowing exceptions and errors

Abstract The specification of abstract data types requires the possibility to treat exceptions and errors. We present an approach allowing all forms of error handling: error introduction, error propagation and error recovery. The algebraic semantics of our method and a new correctness criterion are given. We also introduce an operational semantics of a subclass of our specifications which coincides with the algebraic semantics.

Logics for specifying concurrent information systems

This chapter concentrates on a challenging problem of information system specification and design, namely how to cope on a high level of abstraction with concurrent behaviour and communication as implied by distribution. Since distributed information systems are reactive and open systems maintaining data bases and applications, it is crucial to develop high-level specification techniques that can cope with data and programs as well as with concurrent workflow and communication issues. Techniques from conceptual modeling, abstract data types, concurrent processes and communication protocols are relevant and have to be combined. In the approach presented here, temporal logic is used for specifying sequential object behaviour, and communication facilities are added for specifying interaction between concurrent objects. We study two distributed temporal logics dealing with communication in two different ways. D0 adds basic statements that can only express synchronous “calling” of predicates, while D1 adds much richer facilities for making local statements about other objects in their respective local logics. D0 is more operational and can be animated or implemented more easily, while D1 is intuitively more appealing and convenient for modeling and specification. We demonstrate by example how D1 can be effectively reduced to D0 in a sound and complete way.

Specifying communication in distributed information systems

Abstract. We present two logics that allow specifying distributed information systems, emphasizing communication among sites. The low-level logic

Objects and their Specification

\mbox{\sf D}_0

ALGEBRAIC DOMAIN EQUATIONS

offers features that are easy to implement but awkward to use for specification, while the high-level logic

Local Specification of Distributed Families of Sequential Objects

\mbox{\sf D}_1

Information systems modelling with TROLL formal methods at work

offers convenient specification features that are not easy to implement. We show that

Constructing Systems as Object Communities

\mbox{\sf D}_1