Database Presentation Day 3

Database Presentation Day 3 - Entity Relationship (E-R)...

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vjk - Database Technologies Entity Relationship (E-R) Modeling
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vjk - Database Technologies Quote I created this business, I worked with this business for years, and this is the first time I’ve really understood how all the pieces really fit together -A good database design is the foundation for good applications. -And good database design
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vjk - Database Technologies Basic Modeling Concepts Art and science Good judgment coupled with powerful design tools Models “Description or analogy used to visualize something that cannot be directly observed” Webster’s Dictionary Data Model Relatively simple representation of complex real- world data structures
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vjk - Database Technologies Data Models: Degrees of Data Abstraction
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vjk - Database Technologies Degrees of Abstraction Conceptual Global view of data Basis for identification and description of main data items ERD used to represent conceptual data model Hardware and software independent Internal Representation of database as seen by DBMS Adapts conceptual model to specific DBMS Software dependent
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vjk - Database Technologies Degrees of Abstraction External Users’ views of data environment Provides subsets of internal view Makes application program development easier Facilitates designers’ tasks Ensures adequacy of conceptual model Ensures security constraints in design Physical Lowest level of abstraction Software and hardware dependent Requires definition of physical storage devices and access methods
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vjk - Database Technologies The Entity Relationship (E-R) Model Represents conceptual view Main Components Entities Corresponds to entire table, not row Represented by rectangle Attributes Relationships
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vjk - Database Technologies Attributes Characteristics of entities Domain is set of possible values Primary keys underlined
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vjk - Database Technologies Attributes (contd….) Simple Cannot be subdivided Age, marital status Composite Can be subdivided into additional attributes Address into street, city, zip Single-valued Can have only a single value Person has one social security number
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vjk - Database Technologies Attributes (contd….) Multi-valued Can have many values Person may have several college degrees Derived Can be derived with algorithm Age can be derived from date of birth
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Relationships A relationship is an association between entities. Connected entities are called participants A relationships degree indicates the number of associated entities or participants.
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This note was uploaded on 07/15/2011 for the course ECO 2023 taught by Professor Mr.raza during the Summer '10 term at FAU.

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Database Presentation Day 3 - Entity Relationship (E-R)...

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