Lecture2(1) - 01/11/12 Lecture 2 on Extended Entity...

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Unformatted text preview: 01/11/12 Lecture 2 on Extended Entity Relationship Model This lecture is to describe the methodology of designing an Extended Entity Relationship Model as a conceptual schema for relational database with data semantics of weak entity, cardinality, isa, generalization, aggregation, participation, categorization and n-ary relationship. 01/11/12 Data Model A data model is defined for describing the structure and processing of a database. Database models have two major components: 1. Data definition language(DDL) is a database language that defines the structure of the database data and relationship. It also provides facility for expressing a variety of user views and database constraints. 2. Data manipulation language(DML) is a database language for describing operations on the data that serve to express queries and other manipulation of data. Two types of DML exist: Procedural DML describing actions to be performed (how). Nonprocedural DML describing what data is wanted without describing how to obtain it. 01/11/12 Ansi X4 Architecture of Data Modeling 01/11/12 Data independence 1. Logical data independence The changes of logical schema will not affect the view of the application program processing. 2. Physical data independence The changes of the physical (internal) schema will not affect the application program processing. 01/11/12 Application of data models to database design Database design can be summarized as follows: 1. Begin with the requirements definition. 2. Express tentative conceptual database design in terms of a logical database model. 3. Review design in light of requirements. 4. Convert conceptual design to a logical design using the appropriate logical data model, the one that matches the DBMS to be used. 5. Implement the database using the features of the DBMS. 01/11/12 Use of models in database design Specification Entity-relationship or UML conceptual Schema Relationship Definitions Supporting Documentation Classes Diagrams and Supporting Documentation Conceptual Design Logical Design OR Relational Database implementation Object-Oriented database Implementation Database Design Physical Design 01/11/12 Entity Relationship(ER) Model The Entity Relationship Model is a diagramatic technique for conceptual database design. It serves as an informal representation to model the real world by adopting the more natural view that the real world consists of entities and relationship; and incorporating important semantic information into the model. The model can achieve a high degree of data independence and is based on set theory and relation theory. It can be used for designing conceptual database. 01/11/12 Component of entity-relationship model 1. Entity set an entity set (i.e. entity type) or an entity (i.e. entity instance) is an important distinguishable object for an application....
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This note was uploaded on 01/11/2012 for the course CS CS3462 taught by Professor Drlee during the Spring '11 term at City University of Hong Kong.

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Lecture2(1) - 01/11/12 Lecture 2 on Extended Entity...

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