Brief Introduction to Database Systems

Database

A database is simply an organized collection of related data, typically stored on disk, and accessible by possibly many concurrent users. Databases are generally separated into application areas. For example, one database may contain Human Resource (employee and payroll) data; another may contain sales data; another may contain accounting data; and so on. Databases are managed by a DBMS.

DBMS

A Database Management System (DBMS) is a set of programs that manages any number of databases.

A DBMS is responsible for:

• accessing data
• inserting, updating, and deleting data
• security
• integrity, facilitated by:
  • locking
  • logging
  • application-defined rules, including triggers
• supporting batch and on-line programs
• facilitating backups and recoveries
• optimizing performance
• maximizing availability
• maintaining the catalog and directory of database objects
• managing the buffer pools
• acting as an interface to other systems programs
• supporting user interface packages, such as the popular SQL interface for relational database systems

There are 3 traditional types of database management systems: hierarchical, relational, and network. Current popular database systems include Oracle; Sybase (same as Microsoft's SQL Server but on a different platform); IBM's DB2, IMS, and SQL/DS; Ingres; Informix; and smaller, but reasonably powerful off-the-shelf products such as dBase, Access, Foxpro, Paradox, and dozens of others.

The choice of a database product is often influenced by factors such as:

• the computing platform (i.e., hardware, operating system)
• the volume of data to be managed
• the number of transactions required per second
• existing applications or interfaces that an organization may have
• support for heterogeneous and/or distributed computing
• cost
• vendor support

Object-oriented database systems are currently in development. They allow us to model and manipulate complex data structures and objects, and hence support many new applications, including CAD/CAM. As of 1996, object-oriented databases represent a very small segment of the commercial market (perhaps 1%). It is interesting to note that some major DBMS vendors are starting to support complex objects (such as images) in their relational products.

SQL

Structured Query Language is perhaps the most common way to extract data from a relational database system. The (simplified) format is:

        SELECT  field name(s)
        FROM    database's table name(s)
        WHERE   conditional clause
        

For example, to find all professors earning more than $75,000, a suitable query might be:

        SELECT  name, salary
        FROM    payroll
        WHERE   job = 'Professor' and salary > 75000
        

Berkeley's List of DBMS Vendors and Standards

Historical Achievements of Database Research

Readings in Database Systems