UML Class Diagram or Entity Relationship Diagram : An Object Relational Impedance Mismatch

It is now nearly 30 years since Peter Chen’s watershed paper “The Entity-Relationship Model –towards a Unified View of Data”. [1] The entity relationship model and variations and extensions to ithave been taught in colleges and universities for many years. In his original paper Peter Chen looked at converting his new ER model to the then existing data structure diagrams for the Network model. In recent years there has been a tendency to use a Unified Modelling Language (UML) class diagram forconceptual modeling for relational databases, and several popular course text books use UMLnotation to some degree [2] [3]. However Object and Relational technology are based on different paradigms. In the paper we argue that the UML class diagram is more of a logical model (implementation specific). ER Diagrams on theother hand, are at a conceptual level of database design dealing with the main items and their relationships and not with implementation specific detail. UML focuses on OOAD (Object Oriented Analysis and Design) and is navigational and program dependent whereas the relational model is set based and exhibits data independence. The ER model provides a well-established set of mapping rules for mapping to a relational model. In this paper we look specifically at the areas which can cause problems for the novice databasedesigner due to this conceptual mismatch of two different paradigms. Firstly, transferring the mapping of a weak entity from an Entity Relationship model to UML and secondly the representation of structural constraints between objects. We look at the mixture of notations which students mistakenly use when modeling. This is often the result of different notations being used on different courses throughout their degree. Several of the popular text books at the moment use either a variation of ER,UML, or both for teaching database modeling. At the moment if a student picks up a text book they could be faced with either; one of the many ER variations, UML, UML and a variation of ER both covered separately, or UML and ER merged together. We regard this problem as a conceptual impedance mismatch. This problem is documented in [21] who have produced a catalogue of impedance mismatch problems between object-relational and relational paradigms. We regard the problems of using UML class diagrams for relational database design as a conceptual impedance mismatch as the Entity Relationship model does not have the structures in the model to deal with Object Oriented concepts Keywords: EERD, UML Class Diagram, Relational Database Design, Structural Constraints, relational and object database impedance mismatch. The ER model was originally put forward by Chen [1] and subsequently extensions have been added to add further semantics to the original model; mainly the concepts of specialisation, generalisation and aggregation. In this paper we refer to an Entity-Relationship model (ER) as the basic model and an extended or enhanced entity-relationship model (EER) as a model which includes the extra concepts. The ER and EER models are also often used to aid communication between the designer and the user at the requirements analysis stage. In this paper when we use the term “conceptual model” we mean a model that is not implementation specific.ISBN: 978-84-616-3847-5 3594Peer reviewe

The Use of UML Class Diagrams To Teach Database Modelling and Database Design

It is now nearly 30 years since Peter Chen’s watershed paper “The Entity-Relationship Model – towards a Unified View of Data”. [1] The entity relationship model and variations and extensions to it have been taught in colleges and universities for many years. In his original paper Peter Chen looked at converting his new ER model to the then existing data structure diagrams for the Network model. In recent years there has been a tendency to use a Unified Modelling Language (UML) class diagram for conceptual modelling for relational databases, and several popular course text books use UML notation to some degree [2] [3]. This paper looks at the usefulness of using UML class diagrams for teaching database design in undergraduate courses. In this paper we look specifically at two concepts which can cause problems for the novice database designer. Firstly transferring the concept of a weak entity from an Entity Relationship model to UML and secondly the notation for structural constraints in different diagramming notations. We also look at the mixture of notations which students mistakenly use when modelling. This is often the result of different notations being used on different courses throughout their degree. Peter Chen wrote in his original paper “The entity-relationship model can be used as a tool in the structured design of databases using the network model” today we could write “the UML class diagram can be used as a tool in the structured design of databases using the relational model”. Or can we

Pragmatization of Conceptual Modelling

The aim of this paper is to show how speech act theory can be used in systems development as a theoretical foundation for conceptual modelling. With the traditional notion of the conceptual model as an image of reality, the predominant modelling problem is to analyse how the external reality should be mapped into, and represented in, the system in a ‘true’ way. In contrast to this, we maintain that the main modelling problem should be to analyse the communication acts performed by use of the system within its business context. This implies an integration of traditional conceptual modelling with action-oriented business modelling based on speech act theory. With such an approach it is possible to reconcile traditional conceptual modelling and the pragmatic aspects of language and computer use. It is argued that such reconciliation is essential to arrive at systems that provide relevant information to users and in which users can trace responsibilities for information, actions and commitments made

Microsoftin Common Data Modelin yleistettävyys Master Data Management-kontekstissa

Käsitetietomallinnus on tarpeellinen, mutta resursseja vievä osa dataprojektia. Se ei myöskään välttämättä tuota arvoa, sillä asiakkaan tai ihmisten tapaiset yleiset kohdealueet ovat hyvin samankaltaisia tietosisällöltään organisaatiosta riippumatta. Tämä pätee erityisesti Master Dataan, joka pyrkii löytämään organisaation olennaisimman ydintiedon ja tällainen data on yleensä samankaltaista organisaatioissa. Referenssitietomallit tarjoavat ongelmaan mahdollisen ratkaisun ja niillä on mahdollista siirtää resursseja mallinnustyöstä arvoa tuottavaan työhön, kuten datan laadun hallintaan ja informaatiosta saataviin löydöksiin. Jotta käsitetietomalli voisi palvella Master Data-tarkoitusta, täytyy sen olla yleistettävä ja riittävän pitkälle normalisoitu, jotta sen rakenne takaa organisaation ydintiedon laadun. Normalisaation työkaluna toimii funktionaalisten riippuvuuksien tarkastelu. Microsoftin Dynamics 365-asiakkuushallintajärjestelmään pohjautuva Common Data Model on esimerkki referenssitietomallista ja tässä opinnäytteessä keskitytään sen Account-entiteettityyppiin, joka vastaa asiakasta tai liikekumppania. Tutkielmaa tehdessä havaittiin, että vaikka CDM:n Account-entiteetissä on paljon puoltavia tekijöitä, kuten kattava metadata asiakastiedon hallintaan, käsitemalli on teknisesti liian kytköksissä Dynamics-taustaan ja liian denormalisoitu, että sitä voisi suositella yleiseen käyttöön Master Data-hankkeissa

Reforming Peru’s Political Institutions : The Role of Good Governance Aid as a Driver of Change

Decades-long debates over the quality, quantity and purpose of development aid have led to a renewed emphasis on whether, and under what circumstances, aid is effective in achieving development outcomes. There is significant policy consensus that aid is most effective in environments with “good” governance, which the United Nations defines as processes of decision making and implementation that are effective and efficient, equitable and inclusive, and accountable and transparent. Aid donors fund numerous projects aimed at strengthening good governance in recipient countries, often through reforms of political institutions. Yet many aid donors fail to theorize about the process or mechanism through which good governance aid drives institutional change, and in doing so often ignore the impact that other drivers of change may have on the implicitly assumed direct causal relationship between aid and improved governance in political institutions. This thesis explores the role of aid in shifting institutions toward the ideal of good governance through an analysis that embeds this aid within a larger context that takes into account the role of other drivers of change. It compares good governance-related changes within Peru’s judicial institutions and Comptroller (Auditor) General over a 30-year period, from 1980-2010, examining the main actors and factors that drove or influenced changes in institutional accountability, transparency, effectiveness and efficiency, asking how they drove these changes and overcame resistance to reforms. Building upon this within-case analysis, this thesis then compares across cases to develop conclusions about the necessary and sufficient conditions that resulted in positive good governance-related changes. It concludes with a discussion of the opportunities for, and limitations of, good governance aid as a driver of change in political institutions

Export opportunities: women workers organising in the Philippine garments industry

Transnational production arrangements have been widely argued to lessen the organising capacities of industrial workers, none more so than in the case of women workers in 'export' or 'world market' factories in developing countries. This thesis contests this assertion by showing that women workers' ability to form enterprise unions in the Philippine garments industry are enhanced by transnational production arrangements involving an overseas market. Specifically, the thesis demonstrates that, in order to meet the quality and delivery requirements of overseas buyers and contractors, local owners and/or production managers are forced to routinely keep more production in-house in order to exert more direct controls over the work processes of their women sewers. By thereby limiting the amount of local subcontracting which is done, women workers are agglomerated in larger numbers in the one place and, consequently, their capacities to engage in collective action - as indicated by the establishment of enterprise unions - is markedly increased. Empirically, the argument of the thesis draws on a 'multiple-case' study of sixty-five garment-making establishments located in and around Manila. The study involved interviews with owners, production managers and/or trade union officials about the local subcontracting practices of their establishments. The conclusions drawn about the links between export production and enhanced labour organising capacities at the enterprise level are corroborated by the 'commodity chain' literature on industrial deepening in the international garments industry and the status of the Philippine industry in this regard. But rather than think simply in terms of industrial deepening, this thesis is concerned with the impacts of exporting on class processes. Theoretically, the thesis thus draws on the Marxist view that capitalist development entails changes in the social form of labour, through the real subsumption of labour. But, whereas Marx linked the real subsumption of labour to greater capitalist controls over the labour process, in this thesis the real subsumption of labour is also tied to concomitant changes in the spatial form of the labour process. From this standpoint, the thesis engages with labour process theory after Braverman (accusing it of often failing to link capitalist control to class processes) and with theories of class (which often ignore the social and spatial form of the labour process). In tying organising capacities of women workers at the enterprise level to changes in social and spatial form of the labour process, it is nevertheless argued that these capacities are also shaped at the national level by the legal framework for legitimate organising and by 'political space' in which the law in fact operates. In this regard, it is argued that, whilst the state often passes laws to protect labour standards, it does not grant workers the means to ensure such standards are actually enforced. The thesis also challenges the view that the recruitment of women is a strategy which employers deliberately use in the Philippine garments industry to limit industrial conflict. Against this assertion of a rational economic basis to women's employment, the thesis argues that women are employed for sewing jobs as a result of the sex-typing of such jobs; but that this is also more an effect than a cause as the feminisation of sewing in the modern garments industry is embedded in class processes in the nineteenth century in Europe and the United States. Gender is a dimension of labour control, but women workers in the garments industry are not employed to limit enterprise unionism