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9 Cards in this Set

  • Front
  • Back
Database
a collection of information that you organize and access according to the logical structure of that information.
Relational database
uses a series of logically related two-dimensional tables or files to store information in the form of a database.
Modeling Reality
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
The Conceptual Model (ER diagram)
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
An Entity
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
An Attribute
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
Identifiers
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
Relationships
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
Relationship Cardinality
Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.