Flat-File Databases
A database file that consists of a single data table is called a flat-file database, useful for a single user or small group, such as an address list. Disadvantages include redundant data, typographical input errors, and problems with updating and modifying data.
Database Management Systems (DBMS)
A DBMS is general-purpose software used to create, modify and extract information from a database, keeping all data centrally so only authorized users can access it. It consists of the database itself (DB) and a set of application programs used to access, update and manage data (the management system, MS).
Features of a DBMS
- Queries: extract data using a language such as Structured Query Language (SQL).
- Forms and reports (see Database Structure lesson).
- Models define rules and standards for all data in the database.
- Data mining: using software to search through data from many sources looking for connections.
Main Objectives of a DBMS
- Control of data redundancy: eliminates redundancy by integrating files so multiple copies aren’t stored.
- Data consistency: if a data item is stored once, any update is available immediately to all users.
- Improved data integrity: validity and consistency of stored data, expressed as constraints that must not be violated.
- Improved security: protecting the database from unauthorized users, restricting access by operation type (retrieval, insert, update, delete).
- Increased concurrency: managing simultaneous access by multiple users so accesses don’t interfere with each other.
- Improved backup and recovery: minimizing processing lost following a failure.
Examples of DBMS: Oracle, PostgreSQL, Sybase, MySQL, Microsoft Access, SQL Server, DB2, Open Office Base.
Database Languages
Structured Query Language (SQL) has become the standard relational database language. Ideally, a database language should allow a user to create the database and relation structures, perform basic data management tasks (insertion, modification, deletion), and perform both simple and complex queries.
- Data Definition Language (DDL): a special language used to specify a database schema – it defines the database structure and controls access to the data.
- Data Manipulation Language (DML): enables users to access or manipulate data as organized by the appropriate data model, covering selection/retrieval, insertion, deletion and updating of information stored in a table.
