Database Systems vs File Systems

• Key features differentiate a database approach compared to file programming

Traditional File Processing

• Each user must individually define and implement needed files for their specific software application
• This can lead to redundancy

Database Approach

• Data names and labels are defined once
• Data names and labels are used repeatedly by queries, transactions, and applications

Main Characteristics of the Database Approach

• Self-describing nature of a database system
• Insulation between programs and data
• Data abstraction
• Support of multiple views of the data
• Sharing of data and multi-user transaction processing

Self-Describing Nature of Database System

• A DBMS catalog stores the description of the database structure and constraints, such as data structures, types, storage format, and constraints.
• The DBMS catalog description is called meta-data
• This allows the DBMS software to work with different database applications
• A simplified database catalog includes 'Relations' and 'Columns'
• 'Relations' consists of 'Relation_name' and 'No_of_columns'
• 'Columns' consists of 'Column_name', 'Data_type', and 'Belongs_to_relation'

Insulation Between Programs and Data

• Insulation between programs and data is called program-data independence
• Insulation between programs and data allows changing data structures and storage organization without changing the DBMS access programs
• The structure of the data files is stored in the DBMS catalog separately from access programs

Data Abstraction

• A data model is a type of Data Abstraction used to hide storage details
• Data model presents users with a conceptual view of the database
• The data model uses logical concepts
• The data model uses objects, their properties, and their interrelationships
• A data model hides storage and implementation details to provide a clear view of the database
• E.g. Internal storage format for a STUDENT record

Support of Multiple Views of the Data

• Each user may see a different view of the database, which describes the data
• E.g. 'Course_name', 'Course_number', and 'Prerequisites' of COURSE_PREREQUISITES

Sharing of Data and Multi-User Transaction Processing

• Allows a set of concurrent users to retrieve from and to update the database
• Care is needed to avoid interferences
• Concurrency control within the DBMS guarantees that each transaction is correctly executed or aborted

Database Users Divisions

• Divided into those who use and control database content and those who design, develop and maintain database applications ("Actors on the Scene")
• Divided into those who design/develop DBMS software and related tools and computer systems operators ("Workers Behind the Scene")

Database Users - Actors on the Scene

• Database administrators are responsible for authorizing access to the database
• Database administrators are responsible for coordinating and monitoring database use
• Database administrators are responsible for acquiring software and hardware resources
• Database administrators are responsible for controlling database use and monitoring efficiency of operations

Database Designers

• They define the content, structure, constraints, and functions/transactions against the database
• They must communicate with end-users and understand their needs
• System analysts determine requirements of end-users and develop specifications
• Application programmers implement specifications as programs; they must be familiar with the DBMS capabilities

End-Users

• End-users use data for queries and reports, and some update database content.
• End-users can be categorized into Casual end users, Naive or Parametric end users, Sophisticated end users, and Standalone end users

Categories of End-Users

• Casual end-users access database occasionally when needed
• Naive or Parametric end-users make up a large section of the end-user population; they use previously well-defined functions
• Examples of Naive or Parametric end-users: bank tellers or university secretaries
• Sophisticated end-users are business analysts, scientists, engineers, others thoroughly familiar with system capabilities
• Sophisticated end-users use tools in the form of software packages that work closely with the stored database
• Stand-alone end-users mostly maintain personal databases using ready-to-use packaged applications
• Examples of Stand-alone end-users: scientists that creates database for their own experiments, or a user that maintains an address book
• You may become sophisticated or stand-alone users

Database Users - Workers Behind the Scene

• DBMS system designers implement the DBMS modules and interfaces as a software package.
• Tool developers design/implement tools (software packages) that facilitate database modeling/design, system design, and improve performance
• Operators/maintenance personnel (system administration personnel) are responsible for running and maintenance of the hardware/software environment

Advantages of Using DBMS Approach

• Controlling redundancy in data storage and in development and maintenance efforts
• Sharing of data among multiple users
• Ensuring consistency of data.
• Restricting unauthorized access to data
• Providing Storage Structures and Search Techniques (e.g. indexes) for efficient query processing
• Providing backup and recovery services
• Providing multiple interfaces to different classes of users
• Representing complex relationships among data
• Enforcing integrity constraints on the database
• Interacting easily with data using high-level dedicated tools

When not to use a DBMS

• When the main inhibitors (costs) of using a DBMS are a high initial investment and a possible need for additional hardware
• When the main inhibitors (costs) of using a DBMS is overhead for generality, security, concurrency control, recovery, and integrity functions
• When it may be unnecessary if the database and applications are simple, well defined, and not expected to change
• When it may be unnecessary if there are stringent real-time requirements that may not be met because of DBMS
• When it may be unnecessary if access to data by multiple users is not required
• When no DBMS may suffice if the database system cannot handle complexity of data because of modeling limitations
• When no DBMS may suffice if the database users need special operations not supported by the DBMS