It is argued that ontologically clear entity relationship models can model the real world domains more accurately than ontologically unclear models. However, transformation of such models into the relational model at the logical level has not yet been studied sufficiently with a view to formulate new transformation rules. This paper presents a set of new transformation rules to convert ontologically clear conceptual models to relational models. Finally we did a comparison of two relational models that were developed from the ontologically clear and unclear models using a quality criterion synthesized from the extant literature. The preliminary results of this ongoing research study shows that the quality of relational model developed from ontologically clear conceptual model is superior to its ontologically unclear counterpart.
Conceptual modeling is an activity undertaken during the early stages of information systems development work, where a graphical diagram representing the real word phenomena of an application domain is produced. Researchers have enhanced the expressive power of a wellknown conceptual modeling methodology, the entity relationship (ER) model , using an ontology  that can describe the structure and the behavior of the real world. These models are called ontologically clear entity relationship diagrams (OC-ERD)  .
In order to take the advantage of OC-ERDs, such models should be properly transformed into a relational database schema (RDS) [9, 10] without losing the semantics of the OC-ERD. The current set of rules developed to transform generic ERDs is not fully applicable for OC-ERDs. As such, this paper presents some preliminary results of an ongoing research study undertaken to develop new transformation rules and a method of evaluating the quality of the relational model derived from such rules.
The rest of the paper is organized as follows. Accordingly, the section II demonstrates an ontologically unclear ERD (OUC-ERD) of a particular real world scenario and its transformation together with issues of transformation. Section III presents the ontologically clear version of the OUC-ERD, the OC-ERD, and issues of transforming it using the existing algorithm. The section also presents a new algorithm proposed and the transformation using it. Then in section IV, we propose a quality criteria for assessing the quality of the two types of RDSs resulted from both approaches and present the quality comparison. Finally we discuss the preliminary results and the future work of this ongoing research study in the section V.
II. LOGICAL DATABASE DESIGN ISSUES WITH OUCERDS
We now present an OUC-ERD and issues of transforming it to the relational model using the existing ER to relational transformation algorithm.
Fig 1 is an OUC-ERD representing a company in the real world. The diagram contains a binary 1:1(one-to-one) and optional relationship type “Manages” between two entity types “Employee” and “Department”. The cardinality ratio (0, 1) between the Employee entity type and the relationship type has two meanings i.e. an employee may not manage a department or an employee who manages a department can manage only one department. The “StartDate” attribute represents the date an employee starts managing a particular department.
Optional relationships like the one above are believed to be difficult to understand by typical domain users. Ontology proscribes the use of optional relationship types and advises using mandatory relationship types with subtyping . Accordingly, the diagram depicted in Fig 1 is an ontologically unclear ER diagram (OUC-ERD).
The existing transformation algorithm proposed by Elmasri and Navathe  is given below. For each regular entity type E in the ER schema, create a relation L that includes all the attributes of E. Choose one of the key attributes of E as the primary key of L.
For each binary 1:1 relationship type in the ER schema, identify the relations S and T that correspond to the entity types that participating in R. Choose one of the relations – S, say- and include as a foreign key in S the primary key of T. Include all the simple attributes of R as attributes of S.