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9 Cards in this Set
- Front
- Back
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Database
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a collection of information that you organize and access according to the logical structure of that information.
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Relational database
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uses a series of logically related two-dimensional tables or files to store information in the form of a database.
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Modeling Reality
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A database must mirror the real world if it is to answer questions about the real world
Data Modeling is a design technique for capturing reality |
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The Conceptual Model (ER diagram)
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representation of structure and constraints of database independent of software
Mainstream approach to conceptual modeling is ERD ease of use CASE support No standard notation Building blocks are entities, attributes, relationships, and identifiers Emphasis – no data redundancy |
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An Entity
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Something of interest in the environment (e.g., person, place, object, event, concept)
Represented in E-R diagram by a rectangle An instance is a particular occurrence of an entity |
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An Attribute
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A discrete data element
Describes an entity (i.e., is a characteristic) Meaningful (for the system being modeled) Attributes are the items of interest to the organization -- the things being stored |
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Identifiers
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Every instance of an entity must be uniquely identified (to unambiguously distinguish them)
An identifier can be one or more attributes (e.g., first name, middle name, and last name) Create an identifier if there is no obvious identifying attribute (e.g., part number) Underline identifiers in diagrams |
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Relationships
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A relationship is an association between the instances of one or more entities
The degree of a relationship indicates the number of entities involved The cardinality of a relationship describes the number of instances of one entity associated with another entity |
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Relationship Cardinality
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Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.
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