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