Uwe Hohenstein

Towards a semantic view of an extended entity-relationship model

Nearly all query languages discussed recently for the Entity-Relationship (ER) model do not possess a formal semantics. Languages are often defined by means of examples only. The reason for this phenomenon is the essential gap between features of query languages and theoretical foundations like algebras and calculi. Known languages offer arithmetic capabilities and allow for aggregates, but algebras and calculi defined for ER models do not. This paper introduces an extended ER model concentrating nearly all concepts of known so-called semantic data models in a few syntactical constructs. Moreover, we provide our extended ER model with a formal mathematical semantics. On this basis a well-founded calculus is developed taking into account data operations on arbitrary user-defined data types and aggregate functions. We pay special attention to arithmetic operations, as well as multivalued terms allowing nested queries, in a uniform and consistent manner. We prove our calculus only allows the formulation of safe terms and queries yielding a finite result, and to be (at least) as expressive as the relational calculi.

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.

SQL/EER—syntax and semantics of an entity-relationship-based query language

Abstract This paper presents the high-level query language SQL/EER for an extended Entity-Relationship model (EER model). SQL/EER directly supports all the concepts of the EER model and takes into account well-known features that are integral part of contemporary query languages, e.g. arithmetic and aggregate functions. In contrast to usual descriptions of query languages, we give SQL/EER a complete formal specification of syntax and semantics. The syntax is defined by using an attribute grammar which fixes the context-free structure and the context-sensitive rules. The operational semantics is defined by formally translating SQL/EER queries into queries of an existing, semantically well-defined calculus. The attribute grammar is extended to cover this translation, too. The query language SQL/EER is used in a database design environment. In this context, the formal specification of its syntax and the semantics has been used to implement a syntax-directed editor and a query interpreter for SQL/EER.

Bridging the Gap Between C++ and Relational Databases

This work presents a new approach to access existing relational databases from C++ programs in an easy and natural way. The coupling of both worlds makes use of data reverse engineering techniques. Semantics that is inherent to relational data is made explicit by using object-oriented concepts extensively. Relationships and subtypes are expressed directly in order to take great benefit of them. C++ application programs are thus given the ability to handle relational data as if they were C++ objects.

Supporting data migration between relational and object-oriented databases using a federation approach

Data migration between relational and object-oriented database systems is useful whenever relational data is needed in new object-oriented environments. However, implementing migration programs, i.e. converting and loading legacy data into the new database system, is cumbersome and must be done for each pair of databases manually. This paper presents a flexible approach to support data exchange using a federation approach. Given any relational database, a migration program for filling an object-oriented database is generated. The other direction can be automated in the same way.

Three-Level-Specification of Databases using an extended Entity-Relationship Model

A great deal of (so-called) semantic data models has been proposed for the specification of conceptual schemas. Each of these offers many different, but semantically related constructs for modelling.

A Graphical Tool for Specifying Semantic Enrichment of Relational Databases

Interoperability is a recent technology that meets the needs of new applications requiring access to several heterogeneous databases. In this context, it is important to detect the meaning of data in the various databases. Semantic enrichment is a process that makes inherent semantics explicit by transforming database schemas into a higher data model. Expressive modeling concepts, like relationships and subtypes, are applied to express data semantics.

A Generative Approach to Database Federation

This paper introduces a comprehensive, specification-based approach to database federation, supporting an integrated ODMG-93 conforming access to object-oriented and relational databases. Central point is a set of intuitive specification languages. These languages allow defining ODMG-93 views of existing databases, and building system spanning federated views thereupon. Given concrete specifications defining those views, ODMG schemas are generated automatically due to a generative approach. Heterogeneous databases can be plugged into a federation without implementing adapters for any schema again and again. The generative nature provides flexibility wrt. schema modification of component databases, as new views are implemented automatically. Furthermore, the approach is one of the first to support manipulating federated data seamlessly in C++.

An aspect-oriented implementation of the EJB3.0 persistence concept

This paper demonstrates the power of aspect-orientation by implementation the EJB3.0 persistence framework. Our approach has advantages over existing mapping tools: Flexibility is higher as the functionality can be freely implemented and extended to users needs.

Semantische Anreicherung relationaler Datenbanken

Semantische Anreicherung ist ein Prozes, der die implizit in existierenden Datenbanken vorliegende Semantik explizit macht. Ublicherweise erfolgt die Anreicherung durch eine Transformation des Datenbankschemas in ein semantisch reichhaltigeres Datenmodell. Dabei werden die hoheren Modellierungskonzepte, insbesondere Beziehungen und Subtypen, zur Explizierung der inharenten Semantik verwendet.