DATABASE ENTITY AND CONCEPTUAL DIAGRAMS

Database Entity and Conceptual Diagrams

Database Entity and Conceptual Diagrams

Introduction

This document is an entity-relationship diagram, or “ERD,” for a system to manage electronic resources. An ERD is a model that identifies the concepts or entities that exist in a system and the relationships between those entities. An ERD is often used as a way to visualize a relational database: each entity represents a database table, and the relationship lines represent the keys in one table that point to specific records in related tables. ERDs may also be more abstract, not necessarily capturing every table needed within a database, but serving to diagram the major concepts and relationships. This ERD is of the latter type, intended to present an abstract, theoretical view of the major entities and relationships needed for management of electronic resources. It may assist the database design process for an e-resource management system, but does not identify every table that would be necessary for an electronic resource management database.

This ERD should be examined in close consultation with other components of the Report of the DLF Electronic Resource Management Initiative, especially Appendix E (Data Element Dictionary) and Appendix F (Data Structure). The ERD presents a visual representation of e-resource management concepts and the relationships between them. The Data Element Dictionary identifies and defines the individual data elements that an e-resource management system must contain and manage, but leaves the relationship between the elements to be inferred by the reader. The Data Structure associates each data element with the entities and relationships defined in the ERD. Together, these three documents form a complete conceptual data model for e-resource management.

Overview

Using the three schema approach to software engineering, there are three levels of ER models that may be developed. The conceptual data model is the highest level ER model in that it contains the least granular detail but establishes the overall scope of what is to be included within the model set. The conceptual ER model normally defines master reference data entities that are commonly used by the organization. Developing an enterprise-wide conceptual ER model is useful to support documenting the data architecture for an organization.

A conceptual ER model may be used as the foundation for one or more logical data models. The purpose of the conceptual ER model is then to establish structural metadata commonality for the master data entities between the set of logical ER models. The conceptual data model may be used to form commonality relationships between ER models as a basis for data model integration.

A logical ER model does not require a conceptual ER model especially if the scope of the logical ER model is to develop a single disparate information system. The logical ER model contains more detail than the conceptual ER model. In addition to master data entities, operational and transactional data entities are now defined. The details of each data entity are developed and the entity relationships between these data entities are established. The logical ER model is however developed independent of technology ...