Lecture_5_-_Entity_Relationship_E-R_Modeling

Lecture_5_-_Entity_Relationship_E-R_Modeling - 10/31/2010 1...

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Unformatted text preview: 10/31/2010 1 CSCI-507 Database Theory CSCI-507 Database Theory Lecture 5 Entity Relationship (E-R) Modeling Basic Modeling Concepts Basic Modeling Concepts f Database design is both art and science. f A data model is the relatively simple representation, usually graphic, of complex real-world data structures. It represents data structures and their characteristics, relations, constraints, and transformations. f The database designer usually employs data models as communications tools to facilitate the interaction among the designer, the applications programmer, and the end user. f A good database is the foundation for good applications. 10/31/2010 2 Figure 4.1 Four Modified (ANSI/SPARC) Data Abstraction Models f The Conceptual Model r The conceptual model represents a global view of the data. It is an enterprise-wide representation of data as viewed by high-level managers. r Entity-Relationship (E-R) model is the most widely used conceptual model. r The conceptual model forms the basis for the conceptual schema . r The conceptual schema is the visual representation of the conceptual model. r The conceptual model is independent of both software (software independence) and hardware (hardware independence). Data Models: Degrees of Data Abstraction Data Models: Degrees of Data Abstraction 10/31/2010 3 Tiny College Entities Figure 4.2 A Conceptual Schema for Tiny College Figure 4.3 10/31/2010 4 Data Models: Degrees of Data Abstraction Data Models: Degrees of Data Abstraction f The Internal Model r The internal model adapts the conceptual model to a specific DBMS. r The internal model is software-dependent . r Development of the internal model is especially important to hierarchical and network database models. Figure 4.4 10/31/2010 5 f The External Model r The external model is the end user’s view of the data environment. r Each external model is then represented by its own external schema . CREATE VIEW CLASS_VIEW AS SELECT (CLASS_ID, CLASS_NAME, PROF_NAME, CLASS_TIME, ROOM_ID) FROM CLASS, PROFESSOR, ROOM WHERE CLASS.PROF_ID = PROFESSOR.PROF_ID AND CLASS.ROOM_ID = ROOM.ROOM_ID; Data Models: Degrees of Data Abstraction Data Models: Degrees of Data Abstraction Figure 4.5 The External Models for Tiny College 10/31/2010 6 f The External Model r Advantages of Using External Schemas c It makes application program development much simpler. c It facilitates the designer’s task by making it easier to identify specific data required to support each business unit’s operations. c It makes the designer’s job easier by providing feedback about the conceptual model’s adequacy. c It helps to ensure security constraints in the database design. Data Models: Degrees of Data Abstraction Data Models: Degrees of Data Abstraction f The Physical Model r The physical model operates at the lowest level of abstraction, describing the way data is saved on storage media such as disks or tapes....
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This note was uploaded on 04/15/2011 for the course CSCI 507 taught by Professor Rashid during the Spring '11 term at George Mason.

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Lecture_5_-_Entity_Relationship_E-R_Modeling - 10/31/2010 1...

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