354.ERModel - Database Systems I The Entity-Relationship...

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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 176 Database Systems I The Entity-Relationship Model CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 177 Overview of Database Development Requirements Analysis What data are to be stored in the enterprise? What are the required applications? What are the most important operations? High-level database design What are the entities and relationships in the enterprise? What information about these entities and relationships should we store in the database? What are the integrity constraints or business rules that hold? ER model or UML to represent high-level design
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 178 Overview of Database Development Conceptual database design What data model to implement the DBS? E.g., relational data model Map the high-level design (e.g., ER diagram) to a (conceptual) database schema of the chosen data model. Physical database design What DBMS to use? What are the typical workloads of the DBS? Build indexes to support efficient query processing. What redesign of the conceptual database schema is necessary from the point of view of efficient implementation? CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 179 Overview of Database Development Requirements Analysis / Ideas High-Level Database Design Conceptual Database Design / Relational Database Schema Physical Database Design / Relational DBMS ° Similar to software development
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 180 Entity-Relationship Model Short: ER model. A lot of similarities with other modeling languages such as UML. Concepts Entities / Entity sets, Attributes, Relationships/ Relationship sets, and Constraints. Offers more modeling concepts than the relational data model (which only offers relations). Closer to the way in which people think. CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 181 Entity-Relationship Diagrams An Entity-Relationship diagram ( ER diagram ) is a graph with nodes representing entity sets, attributes and relationship sets. Entity sets denoted by rectangles . Attributes denoted by ovals . Relationship sets denoted by diamonds . Edges ( lines ) connect entity sets to their attributes and relationship sets to their entity sets.
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 182 Entities and Entity Sets Entity: Real-world object distinguishable from other objects, e.g. employee Miller. Entity can be physical or abstract object. An entity is associated with attributes describing its properties. Attribute values are atomic, e.g. strings, integer or real numbers. Some variations of the ER model support structured attributes. Entity set : A collection of similar entities. E.g., all employees. CMPT 354, Simon Fraser University, Fall 2008, Martin Ester 183 Entities and Entity Sets All entities in an entity set have the same set of attributes. (At least, for the moment!) Each entity set has a key , i.e. a minimal set of attributes to uniquely identify an entity of this set. Key attributes are underlined .
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