Databases%20and%20Structured%20Files:%20What%20is%20a%20database?

1
Databases and Structured Files What is a
database?

• A database is a collection of information
• Databases are typically stored as computer files
• A structured file is similar to a card file or
  Rolodex because it uses a uniform format to store
  data for each person or thing in the file

2
Fields What is the basic element of a structured
file?

• A field contains the smallest unit of meaningful
  information, so you might call it the basic
  building block for a structured database
• Each field has a unique field name that describes
  its contents
• A field can be either variable length or fixed
  length.

3
Who defines the structure for the records in a
file?

• The person who creates a data file defines the
  fields it contains
• Each kind of record is referred to as a record
  type
• A record type is similar to a blank form, and it
  is usually shown without any data in the fields
• A record that contains data is referred to as a
  record occurrence, or simply a record.

4
What are relationships?

• In database jargon, a relationship is an
  association between data thats stored in
  different record types
• One important aspect of the relationship between
  record types is cardinality
• Cardinality refers to the number of associations
  that can exist between two record types
• A particular order cannot be placed jointly by
  two customers
• When one record is related to many records, the
  relationship is referred to as a one-to-many
  relationship

5
What are relationships?

• A many-to-many relationship means that one record
  in a particular record type can be related to
  many records in another record type, and vice
  versa
• A one-to-one relationship means that a record in
  one record type is related to only one record in
  another record type
• Relationships between record types can be
  graphically depicted using diagramming
  techniques, such as an entity-relationship
  diagram, sometimes called an ER diagram or
  ERD.

6
Hierarchical, Network, Relational, and
Object-Oriented Databases

• Several database models exist
• Some models work with all of the relationships
  described earlier in this section, whereas other
  models work with only a subset of the
  relationships
• The four main types of database models in use
  today are hierarchical, network, relational, and
  object oriented

7
Whats the simplest database model?

• The simplest database model arranges record types
  as hierarchy
• In a hierarchical database, a record type is
  referred to as a node or segment.
• The top node of the hierarchy is referred to as
  the root node
• A parent node can have more than one child node
• A child node can have only one parent node

8
Whats a relational database?

• It produces databases that are difficult to
  create, manipulate, and maintain
• A relational database stores data in a collection
  of related tables
• Each table (also called a relation) is a
  sequence, or list, of records.
• All of the records in a table are of the same
  record type

9
Whats a relational database?

• A row of the table is called a tuple, and is
  equivalent to a record
• The columns in the table are called attributes,
  and are equivalent to fields
• In a relational database, relationships are
  specified through the use of common data stored
  in the fields of records in different tables