Business Rule Modality pdf file (226K)
Halpin, T. 2006, ‘Business Rule Modality’, Proc. CAiSE’06 Workshops, eds T. Latour & M. Petit, Namur University Press, pp. 383-94.

A business domain is typically constrained by business rules. In practice, these rules often include constraints of different modalities (e.g. alethic and deontic). Alethic rules impose necessities, which cannot, even in principle, be violated by the business. Deontic rules impose obligations, which may be violated, even though they ought not. Conceptual modeling approaches typically confine their specification of rules to alethic rules. This paper discusses one way to model deontic rules, especially those of a static nature. A formalization based on modal operators is provided, and some challenging semantic issues are examined from both logical and pragmatic perspectives. Because of its richer semantics, the main graphic notation used is that of Object- Role Modeling (ORM). However, the main ideas could be adapted for UML and ER as well. A basic implementation of the proposed approach has been prototyped in a tool that supports automated verbalization of both alethic and deontic rules.

Objectification pdf file (159K)
Halpin, T. 2005. ‘Objectification’, Proc. CAiSE’05 Workshops, vol. 1, eds J. Castro & E. Teniente, FEUP, pp. 519-32.

Some information modeling approaches allow instances of relationships or associations to be treated as entities in their own right. In the Unified Modeling Language (UML), this modeling technique is called “reification”, and is mediated by means of association classes. In Object-Role Modeling (ORM), this process is called “objectification” or “nesting”. While this modeling option is rarely supported by industrial versions of Entity-Relationship Modeling (ER), it is allowed in several academic versions of ER. Objectification is related to the linguistic activity of nominalization, of which two flavors may be distinguished: circumstantial; and propositional. In practice, objectification needs to be used judiciously, as its misuse can lead to implementation anomalies, and those modeling approaches that permit objectification often provide incomplete or flawed support for it. This paper provides an in-depth analysis of objectification, shedding new light on its fundamental nature, and providing practical guidelines on using objectification to model information systems. Because of its richer semantics, the main graphic notation used is that of ORM 2 (the latest generation of ORM). However, the main ideas are relevant to UML and ER as well.

Objectification and Atomicity pdf file (292K)
Halpin, T. 2020.

This short paper proposes that objectification should be restricted to fact types with a spanning UC.

Information Modeling and Higher-Order Types pdf file (538K)
Halpin, T. 2004, ‘Information Modeling and Higher-Order Types’, Proc. CAiSE’04 Workshops, vol. 1, (eds Grundspenkis, J. & Kirkova, M.), Riga Tech. University, pp. 233-48.

While some information modeling approaches (e.g. the Relational Model, and Object-Role Modeling) are typically formalized using first-order logic, other approaches to information modeling include support for higher-order types. There appear to be three main reasons for requiring higher-order types: (1) to permit instances of categorization types to be types themselves (e.g. the Unified Modeling Language introduced power types for this purpose); (2) to directly support quantification over sets and general concepts; (3) to specify business rules that cross levels/metalevels (or ignore level distinctions) in the same model. As the move to higher-order logic may add considerable complexity to the task of formalizing and implementing a modeling approach, it is worth investigating whether the same practical modeling objectives can be met while staying within a first-order framework. This paper examines some key issues involved, suggests techniques for retaining a first-order formalization, and also makes some suggestions for adopting a higher-order semantics.

Uniqueness Constraints on Objectifed Associations pdf file (341K)
Halpin, T.A. & Hallock, P. 2003, ‘Uniqueness Constraints on Objectified Associations’, Journal of Conceptual Modeling, October 2003, online at www.inconcept.com.

Unlike UML and some ER versions, ORM currently allows a fact type to be objectified only if it either has a spanning uniqueness constraint or is a 1:1 binary fact type. This article argues that this restriction should be relaxed, and replaced by a modeling guideline that allows some n-ary associations to be objectified even if their longest uniqueness constraint spans n-1 roles. The pros and cons of removing this restriction are discussed, and illustrated with examples.

Join Constraints pdf file (364K)
Halpin, T.A. 2002, ‘Join Constraints’, Proc. Seventh CAiSE/IFIP-WG8.1 International Workshop on Evaluation of Modeling Methods in Systems Analysis and Design, eds. T. Halpin, J. Krogstie, K. Siau, Toronto, Canada, pp. 121-131.

Many application domains involve constraints that, at a conceptual modeling level, apply to one or more schema paths, each of which involves one or more conceptual joins (where the same conceptual object plays roles in two relationships). Popular information modeling approaches typically provide only weak support for such join constraints. This paper contrasts how join constraints are catered for in Object-Role Modeling (ORM), the Unified Modeling Language (UML), the Object-oriented Systems Model (OSM), and some popular versions of Entity-Relationship modeling (ER). Three main problems for rich support for join constraints are identified: disambiguation of schema paths; disambiguation of join types; and mapping of join constraints. To address these problems, some notational, metamodel, and mapping extensions are proposed.

What is an elementary fact? pdf file (73K)
Halpin, T.A. 1993, ‘What is an elementary fact?’, Proc. First NIAM-ISDM Conf., eds G.M. Nijssen & J. Sharp, Utrecht, (Sep), 11 pp.

Database schemas are best designed by mapping from a high level, conceptual schema expressed in human-oriented concepts. While conceptual schemas are often specified using entity relationship modeling (ER), a more natural and expressive formulation is often possible using Object Role Modeling (ORM). This approach views the world in terms of objects playing roles, and traditionally expresses all information in terms of elementary facts, constraints and derivation rules. Although verbalization in terms of elementary facts has many practical and theoretical advantages, it is difficult to define the notion precisely. This paper examines various awkward but practical cases which challenge the traditional definition. In so doing, it aims to clarify what elementary facts are and how they can be best expressed.

Subtyping: conceptual and logical issues pdf file (132K)
Halpin. T.A. 1995, ‘Subtyping: conceptual and logical issues’, Database Newsletter, ed. R.G. Ross, Database Research Group Inc., vol. 23, no. 6, pp. 3-9.
(Note: This newsletter has been replaced by the Business Rules Journal published by Business Rules Solutions, Inc.)

Subtyping is an important feature of semantic approaches to conceptual schema design and, more recently, object-oriented database design. However the relational model does not directly support subtyping, and CASE tools for mapping conceptual to relational schemas typically provide only very weak support for mapping subtypes. This paper surveys some of the main issues related to conceptual specification and relational mapping of subtypes, and indicates how Object Role Modeling solves the associated problems.

Subtyping and Polymorphism in Object Role Modeling pdf file (253K)
Halpin, T. & Proper, H. 1995, ‘Subtyping and polymorphism in Object-Role Modeling’, Data & Knowledge Engineering, vol. 15, North-Holland, Amsterdam,pp. 251-81.

Although entity relationship (ER) modeling techniques are commonly used for information modeling, Object Role Modeling (ORM) techniques are becoming increasingly popular, partly because they include detailed design procedures providing guidelines for the modeler. As with the ER approach, a number of different ORM techniques exist. In this paper, we propose an integration of two theoretically well founded ORM techniques: FORM and PSM. Our main focus is on a common terminological framework, and on the notion of subtyping. Subtyping has long been an important feature of semantic approaches to conceptual schema design. It is also the concept in which FORM and PSM differ the most in their formalization. The subtyping issue is discussed from three different viewpoints covering syntactical, identification, and population issues. Finally, a wider comparison of approaches to subtyping is made, which encompasses other ER-based and ORM-based information modeling techniques, and highlights how formal subtype definitions facilitate a comprehensive specification of subtype constraints.

Flat graphical, conceptual modeling techniques are widely accepted as visually effective ways in which to specify and communicate the conceptual data requirements of an information system. Conceptual schema diagrams provide modelers with a picture of the salient structures underlying the modeled universe of discourse, in a form that can readily be understood by and communicated to users, programmers and managers. When complexity and size of applications increase, however, the success of these techniques in terms of comprehensibility and communicability deteriorates rapidly. This paper proposes a method to offset this deterioration, by adding abstraction layers to flat conceptual schemas. We present an algorithm to recursively derive higher levels of abstraction from a given (flat) conceptual schema. The driving force of this algorithm is a hierarchy of conceptual importance among the elements of the universe of discourse.