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
12/4/2018
CIS270

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.
12/4/2018
CIS270

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.”
12/4/2018
CIS270

4. What are relationships?
In database jargon, a relationship is an association between data that’s 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
12/4/2018
CIS270

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.”
12/4/2018
CIS270

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
12/4/2018
CIS270

7. What’s 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
12/4/2018
CIS270

8. What’s 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
12/4/2018
CIS270

9. What’s 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
12/4/2018
CIS270