Transcript CIS 321 Data Communications & Networking

Introduction to Databases
Angela Clark
University of South Alabama
Databases
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Used to store electronic information
Referred to as secondary storage
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We will discuss
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Benefits for using databases
Database Management Systems
Different database structural formats
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Benefits of Databases
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Data Sharing – information in one department
can be readily shared with other departments
Security – users can be given passwords
and/or access only to the kind of information
they need to know while containing all of the
information in the same database file
Data Redundancy – fewer files are necessary;
data is stored only once and in one location.
This reduces the storage space needed.
Data Integrity – Changes made in the
database will update all occurrences
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Database Management
Systems
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DBMS - special software that allows you to create,
modify, and gain access to a database
data dictionary - contains a description of the
structure of the data used in the database; defines
field names, type of data that can go into the field,
the size of the field, and defines which field is the
key field
query language - allows access to information in
the database; most widely used query language is
SQL (structured query language)
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Database Organization
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Most common types of database formats are:
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Hierarchical Database
Network Database
Relational Database
Object Oriented Database
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Hierarchical Databases
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Structured in nodes (tree like structure)
Each child node has one and only one parent node
(a parent may have more than one child node). We
refer to this as a 1-to-many relationship.
Progress top down to traverse fields. To find
information, you must start at the top with a parent
node and trace down the tree.
Use pointers to connect parent node to child nodes.
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Hierarchical Databases
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Advantages of Hierarchical Databases:
 Efficient and easy to create
Disadvantages of Hierarchical Databases:
 If a parent node is deleted, so are all child nodes
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Cannot add a child node without adding all parent nodes
first
Low flexibility – paths and directories to information must
be specified in advance; very difficult to change
Difficult to maintain
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Network Databases
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Variation on the hierarchical database to
reduce data redundancy
Child nodes can have more than one parent
(many-to-many relationship)
Nodes are reached through pointers; may
provide more than one path to same
information
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Network Databases
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Advantages of Network Databases:
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Efficient
Faster than hierarchical
Less data redundancy
Disadvantages of Network Databases:
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Low flexibility
More pointers; the number of pointers increases
rapidly, which makes it much more complicated to
maintain and operate.
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Relational Databases
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The most flexible – it is not hierarchical in
nature
Uses tables made up of columns and rows
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Columns correspond to Fields
Rows correspond to Records
Related tables can be linked together
through Common Data Elements (keys,
foreign keys)
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Relational Databases
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Advantages of Relational Databases:
 Simple to add, delete, and edit; there are no pointers
 It can relate data in one field in one table to another field
in another table
 Flexible – ad hoc queries can combine data from
different sources
Disadvantages of Relational Databases:
 Slower – may require multiple access to the data
 Requires some data redundancy in order to be more
efficient - the same data must appear in multiple tables
to link the tables
 Must remember to change/update all tables
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Object Oriented Databases
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Handles unstructured data such as
photographs, graphics, audio, video, etc.
Keep track of objects – both data and the
action that can be taken on the object.
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Types of Databases
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Individual – collection of files primarily used by just one
person
Company/Shared – databases that can be used by multiple
users, shared through local area networks
Distributed – data for the database is stored in multiple
locations with access through communication networks
Proprietary – an enormous database developed to cover
particular subject areas; usually offers access to people for
a fee – databanks.
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Questions
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