TAILIEUCHUNG - Lecture Database Systems - Lecture 22

This chapter covers objectbased databases. The chapter describes the object-relational data model, which extends the relational data model to support complex data types, type inheritance, and object identity. The chapter also describes database access from object-oriented programming languages. | CSC271 Database Systems Lecture # 22 Summary: Previous Lecture Applying Database SDLC on DreamHome Database planning System definition Requirements collection and analysis Database design Design methodology Conceptual database design Entity Relationship Modeling Chapter 11 Difficulties in Database Design One of the most difficult aspects of database design is the fact that designers, programmers, and end-users tend to view data and its use in different ways Unfortunately, unless we gain a common understanding that reflects how the enterprise operates, the design we produce will fail to meet the users’ requirements To ensure that we get a precise understanding of the nature of the data and how it is used by the enterprise, we need to have a model for communication that is non-technical and free of ambiguities Solution is the Entity–Relationship (ER) ER-Diagram Notations Different notations are available to represent each concept diagrammatically . Chen notation, Crow’s Feet notation, UML etc. We will use UML due to following reasons: The Object Management Group (OMG) is currently looking at the standardization of UML and it is anticipated that UML will be the de facto standard modeling language in the near future Although we use the UML notation for drawing ER models, we continue to describe the concepts of ER models using traditional database terminology Sample ER-Diagram Concepts of the ER Model The basic concepts of the ER model are: Entity types Relationship types Attributes Entity Types Entity type A group of objects with same properties, which are identified by enterprise as having an independent existence (physical or conceptual) Entity occurrence A uniquely identifiable object of an entity type Examples of Entity Types Diagrammatic Representation: Entity Types Each entity type is shown as a rectangle labeled with the name of the entity, which is normally a singular noun In UML, the first letter of each word in the entity name is upper case Relationship Types

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• Relational databases
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