Relational Databases
Definitions
a database is a collection of related data
a database management system (or DBMS) is a system designed for two main purposes
- to add, delete, and update data in the database
- to provide various ways to view (on screen or in print) the data in the database
a flat file database
is one where all the data is contained in a single table, such as in Excel
a
relational database
is one in which you can store information in different tables, each containing different information that
relates to information in the other tables
comparing flat file databases to relational databases
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Why use a relational database design?
- to eliminate unnecessary redundancy or repetition in storage and in steps required for database maintenance
- to be able to distribute the database to multiple locations, each with a responsibility to maintain a part of the total database
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So a relational database is characterized by
- multiple tables, perhaps maintained by multiple locations
-
with relationships defined between the tables, so that the entire distributed,
relational database works together
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an entity-relationship model (ERM) is an abstract and conceptual representation of data.
Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema
or semantic data model of a system, often a relational database,
and its requirements in a top-down fashion.
Diagrams created by this process are called entity-relationship diagrams (or ER diagrams)
One has choices in how to model the elements in a database.
One of the standard textbooks on the topic (Elmasri, R., & Navathe, S. (2011).
Fundamentals of database systems. Boston: Addison-Wesley.)
offers a view of the several methods.
The purpose of
a database
is to store information about certain types of objects.
- In database language, objects are entities;
- in Access, entities are records
An entity class [like books] is an abstract definition of something
-
an entity (like
the textbook for INLS261)
is
a concrete example
of that description;
- in Access, an entity is a record
An entity class is composed of attributes
in Access, attributes are fields
- they include information we want in the database
-
help to uniquely identify individual
entities
within a class
-
can describe relationships between
entities
in different classes
An entity set is the list
of given entities/records within a given entity
class that are currently in the database/table
in Access, an entity set is a table
Primary and Foreign Keys
-
a Primary Key is a set of
attributes/fields
that uniquely identifies an
entity/a record
-
a Foreign Key is a copy of the Primary Key of one entity class/table
that appears as
an attribute/field
in another entity class/table and helps define the relationship between
entities/records
in the two entity classes/tables
- these keys link together the related entity sets/tables in a relational database
Access Database Design Help
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