A Design for Coordinated and Logics-mediated Conceptual Modelling

Abstract

The past 20 years have seen many e orts to provide logicbased reconstructions of various conceptual modelling languages so as to automatically reason over them, using a myriad of logics and those in the DL family of languages in particular. Subtle di erences in the languages as well as modellers' preferences make it di cult to put the pieces together to provide one uni ed view and system. Therefore, we propose a mechanism to unify the back-end in the tool yet showing linkable ORM, UML, and ER diagrams in the interface. This is achieved by taking a two-pronged approach: 1) supporting full expressiveness of these languages and relying on a unifying metamodel, and 2) a logics back-end for their evidence-driven pro les in DL. Both have a set of rules for inter-model assertions. These pro les are tractable. As a result, we propose an architectural design for a tool that would help to integrate heterogeneous conceptual models and link them with ontologies, based on clear semantic speci cations and with tractable algorithms.

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Data analysis in conceptual data modelling for database and information system development has a long history in computer science, dating back to its introduction in the 1970s. Conceptual data models represent what data will have to be stored and processed in a particular system, and the constraints among them in that `universe of discourse' of the application. These models are almost exclusively represented graphically, using lines, boxes, diamonds, or ellipses, and the various adornments for the constraints. Many conceptual modelling languages are being used, such as UML Class Diagrams [ 25 ], EER [ 7, 31 ], ORM [ 17 ], MADS [ 27 ], and Telos [ 24 ], with as many tools to support them or, more often, a subset of their features, e.g., SmartDraw, MS Visio, GenMyModel, OmniGra e, ERwin, NORMA, and ArgoUML. Conceptual modelling is used in industry, with experiments showing that it is being used notably in small (< 100) and large (> 1000) organisations, increasingly by modellers up to 10 years of experience, using modelling and CASE tools [ 8 ].

With increasingly complex system development and systems integration, the conceptual models become larger, their languages tend to acquire more features, and have more complex interactions because the components of the systems have to, and it is not unusual to use di erent modelling languages for the different components. A typical scenario is to use an ER diagram for the planned relational database and a UML Class Diagram for the application layer. Also, modellers have certain preferences for notation. The other main scenario is conceptual model-based data integration. In this case, one or more elements in each model needs to be linked across models that may be represented in di erent languages. This requires either one representation language or a common metamodel. Metamodel-based approaches by the conceptual modelling community typically analyse di erences [ 15 ] rather than trying to nd commonalities. In the Description Logics (DL) community, on the other hand, some e ort has gone into trying to unify them in that all the di erent graphical depictions would end up as `syntactic sugar' with a logic-based reconstruction into one suitable DL in the background hidden from the modeller [ 5, 21 ]. Most works, however, have focussed on logic-based reconstructions so as to be more precise and for automated reasoning over conceptual models to improve their quality; e.g., [ 1, 2, 16, 18, 19, 29 ] (though also other logics are being used, including OCL [ 28 ], CLIF [ 26 ], and Alloy [ 4 ]). Zooming in on DLs, ALU N I was used for a partial uni cation [ 5 ], whereas others are used for particular modelling language formalisations, such as DL-Lite and DLRifd [ 1, 2 ], or OWL, which may have o er only incomplete coverage of the full modelling language, such as omitting ER's `keys' (identi ers) [ 5 ] or n-aries proper [ 1 ], among many variants. Also, multiple formalisations in multiple logics for one conceptual modelling language have been published (e.g., [ 14, 16, 18, 20 ] for ORM), and ORM in full is undecidable. Most of these e orts aim to cover most, or all, modelling language features. In contrast, a separate track of works looks at lean fragments so as to use the formalised conceptual data model at runtime. These lean pro les can be used for, among others, scalable test data generation [ 30 ], designing [ 3 ] and executing [ 6 ] queries, or querying databases during the stage of query compilation [ 32 ].

Thus, the reality is that there are multiple conceptual modelling languages that neither will go away nor will be superseded by just one language, with many logic-based reconstructions in multiple logics that seek to solve di erent problems, with more or less tools that are not designed to be interoperable. This raises the need for the integration of model design and their respective compatible formalisations, and to do this in a common tool. We aim to develop such a tool by building upon and extending ICOM [ 10, 13 ] that used a tailormade single graphical language, single logic (ALCQI), and reasoner (Racer). In particular, we are working on the following three major changes: 1. the graphical interface, such that modellers can model in UML Class Diagram notation in one model (module), in EER in another, and in ORM notation in yet another, with each model checked against a unifying metamodel for correctness regarding syntax; 2. the logic-based reconstructions, targeting a multi-modal approach, i.e., with one as comprehensive as the modelling language, caring little about performance, and, in the rst instance, another mode with an evidence-based core pro le for the three conceptual data modelling language families that is computationally well-behaved; 3. the support for inter-model assertions so as to handle also cross-modelling language assertions, to allow also for attribute links, and to allow for approximations with common `type' conversions, such as Attribute$Value Type.

Verifying such links relies on rules as well as the metamodel.

The high-level orchestration of the components is depicted in Fig. 1, with at its centre the DLs and their automated reasoners. This feature set is substantially di erent from ICOM's scope. The theoretical foundations and evidence obtained with experiments are based on a series of papers, which are the outcome of the project \Ontology-driven uni cation of conceptual data modelling languages" [http://www.meteck.org/SAAR.html] that was funded by Argentina's and South Africa's respective Ministries of Science and Technology.

The ontology-driven metamodel unifying UML Class Diagram v2.4.1, EER, and ORM2 and the metamodel's formalisation are described in [ 23, 9 ], which the left-hand side of Fig. 1 relies on. The approach for the inter-model link checker and core transformation rules (right-hand side of Fig. 1) are described in [ 12 ]. This approach avails of the metamodel to direct the checking of the intermodel assertions. The language pro les|at the centre of Fig. 1|are described in [ 11 ], which are based on an experimental evaluation of 101 conceptual models on the language features used in publicly available models [ 22 ]. Interestingly, the language pro les are tractable, and thus could be used for run-time usage of ontologies in an ontology-driven information system, such as proposed by [ 6, 30, 32 ].

We are currently developing a web-based prototype of the tool that involves the rst two components in Fig. 1. A user edits a conceptual model on a web browser, while reasoning services are hosted on the server. For the moment, exclusive access to the model is given to the user. Simultaneously editing of the same model is planned in future versions.

graphics files for EER, UML, ORM2

checks metamodel frament files for EER, UML, ORM2 Metamodel-driven checker (syntax) formalised logic files for core profile as for EER, UML, ORM2 merged into

uses automated reasoner linked theory

Transformation rules consults

metamodel DL-based checker (semantics)

Inter-model links checker (rules with metamodel)

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