BU486 Chapter Notes - Chapter 4: Data Dictionary, Data Modeling, Tuple

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27 May 2018
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Chapter 4 Relational Databases
Database set of interrelated, centrally coordinated data files that are stored with a little data
redundancy as possible
Advantages of a Database
Data is integrated
Data sharing
Minimize redundancy and inconsistencies
Data is independent of the programs
Easily accessed for reporting and cross functional analysis
Logical Views how people conceptually organize and understand the relationships among data items
Physical view internal level of the database, which is how the data is actually physically stored in the
system
Schemas description of the data elements in a database, the relationships among them, and the logical
model used to organize and describe the data
Conceptual level organization wide view, lists all data elements and the relationships between
them
External level indiidual user’s ie
Internal level low level view, describes how the data are stored and accessed
DBMS Languages
Data Definition Language (DDL)
o Builds the data dictionary, which is information about the structure of the database
including a description of each data element stored in the database
o Creates the database
o Describes logical views for each user
o Specifies record or field security constraints
Data Manipulation Language (DML)
o Changes the content in the database
Data Query Language (DQL)
o Enables users to retrieve, sort, and display specific data from the database
Relational Database represents conceptual and external level schemas as if data are stored in two
dimensional tables, e.g. rows and columns
Primary keys an attribute in a table
Foreign key an attribute in a table that is also a primary key in another table, used to link the
two tables
Why have a set of related tables
Data stored in one large table can be redundant and inefficient causing the following problems:
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