Basic Concepts
You are now beginning to appreciate the significance of the database approach.You
are discerning the major benefits of developing and using applications in a database
environment. Before proceeding further, let us review a few fundamental concepts
and become familiar with some key terminology.
Data Repository All data in the database reside in a data repository. This is the
data storage unit where physical data files are kept. The data repository contains
the physical data. Mostly, it is a central place of storage for the data content.
Data Dictionary The data repository contains the actual data. Let us say that you
want to keep data about the customers of your company in your database.The structure
of a customer’s data could include fields such as customer name, customer
address, city, state, zip code, phone number, and so on. Data about a particular
customer could be as follows in the respective fields: Jane Smith/1234 Main
Street/Piscataway/NJ/08820.There are two aspects of the data about customers.One
aspect is the structure of the data consisting of the field names, field sizes, data types,
and so on. This part is the structure of the data for customers. The other part is the
actual data for each customer consisting of the actual data values in the various
fields.
The first part relating to the structure resides separately in storage, and this is
called the data dictionary or data catalog. A data dictionary contains the structures
of the various data elements in the database. It also contains the relationships
among data elements. The other part relating to the actual data about individual
customers resides in the data repository. The data dictionary and the data repository
work together to provide information to users.
Database Software Are Oracle and Informix databases? Oracle and Informix
are really the software that manages data. These are database software or database
management systems. Database software supports the storing, retrieving, and updating
of data in a database. Database software is not the database itself. The software
helps you store, manage, and protect the data in a database.
Data Abstraction Consider the example of customer data again. Data about each
customer consist of several fields such as customer name, street address, city, state,
zip code, credit status, and so on.We can look at customer data at three levels. The
customer service representative can look at the customer from his or her point of
view as consisting of only the fields that are of interest to the representative. This
may be just customer name, phone number, and credit status. This is one level. The
next level is the structure of the complete set of fields in customer data. This level
is of interest to the database designer and application programmer. Another level
is of interest to the database administrator, who is responsible for designing the
physical layout for storing the data in files on disk storage.
Data Access The database approach includes the fundamental operations that
can be applied to data. Every database management system provides for the following
basic operations:
• READ data contained in the database
• ADD data to the database
• UPDATE individual parts of the data in the database
• DELETE portions of the data in the database
Database practitioners refer to these operations by the acronym CRUD:
• C—Create or add data
• R—Read data
• you—Update data
• D—Delete data
Transaction Support Imagine the business function of entering an order from a
customer into the computer system. The order entry clerk types in the customer
number, the product code, and the quantity ordered. The order entry program reads
the customer data and allows the clerk to sight verify the customer data, reads
product data and displays the product description, reads inventory data, and finally
updates inventory or creates a back order if inventory is insufficient. All these tasks
performed by the order entry program to enter a single order comprise a single
order entry transaction
You are now beginning to appreciate the significance of the database approach.You
are discerning the major benefits of developing and using applications in a database
environment. Before proceeding further, let us review a few fundamental concepts
and become familiar with some key terminology.
Data Repository All data in the database reside in a data repository. This is the
data storage unit where physical data files are kept. The data repository contains
the physical data. Mostly, it is a central place of storage for the data content.
Data Dictionary The data repository contains the actual data. Let us say that you
want to keep data about the customers of your company in your database.The structure
of a customer’s data could include fields such as customer name, customer
address, city, state, zip code, phone number, and so on. Data about a particular
customer could be as follows in the respective fields: Jane Smith/1234 Main
Street/Piscataway/NJ/08820.There are two aspects of the data about customers.One
aspect is the structure of the data consisting of the field names, field sizes, data types,
and so on. This part is the structure of the data for customers. The other part is the
actual data for each customer consisting of the actual data values in the various
fields.
The first part relating to the structure resides separately in storage, and this is
called the data dictionary or data catalog. A data dictionary contains the structures
of the various data elements in the database. It also contains the relationships
among data elements. The other part relating to the actual data about individual
customers resides in the data repository. The data dictionary and the data repository
work together to provide information to users.
Database Software Are Oracle and Informix databases? Oracle and Informix
are really the software that manages data. These are database software or database
management systems. Database software supports the storing, retrieving, and updating
of data in a database. Database software is not the database itself. The software
helps you store, manage, and protect the data in a database.
Data Abstraction Consider the example of customer data again. Data about each
customer consist of several fields such as customer name, street address, city, state,
zip code, credit status, and so on.We can look at customer data at three levels. The
customer service representative can look at the customer from his or her point of
view as consisting of only the fields that are of interest to the representative. This
may be just customer name, phone number, and credit status. This is one level. The
next level is the structure of the complete set of fields in customer data. This level
is of interest to the database designer and application programmer. Another level
is of interest to the database administrator, who is responsible for designing the
physical layout for storing the data in files on disk storage.
Data Access The database approach includes the fundamental operations that
can be applied to data. Every database management system provides for the following
basic operations:
• READ data contained in the database
• ADD data to the database
• UPDATE individual parts of the data in the database
• DELETE portions of the data in the database
Database practitioners refer to these operations by the acronym CRUD:
• C—Create or add data
• R—Read data
• you—Update data
• D—Delete data
Transaction Support Imagine the business function of entering an order from a
customer into the computer system. The order entry clerk types in the customer
number, the product code, and the quantity ordered. The order entry program reads
the customer data and allows the clerk to sight verify the customer data, reads
product data and displays the product description, reads inventory data, and finally
updates inventory or creates a back order if inventory is insufficient. All these tasks
performed by the order entry program to enter a single order comprise a single
order entry transaction
