Databases and Database Management Systems What is a

Databases and Database Management Systems

What is a database? n n A database is a file of similarly structured records. A database is a collection of information related to a particular subject or purpose, such as tracking customer orders or maintaining a music collection.

What is a database management system (DBMS)? n n n A database management system is software that allows you to manage all your data in a systematic fashion. It allows you to design and create new databases and perform various operations on existing databases. These operations include adding new data and retrieving, modifying or deleting existing data.

Types of DBMS architectures n n n Network (e. g. Cullinet Software’s IDMS) Hierarchical (e. g. IBM’s IMS) Relational (the most common in use today) Object-relational Object

Example relational DBMSs n “Large” n n Oracle DB 2 (IBM) Informix Sybase n “Small” n n Access (Microsoft) Fox. Pro d. Base 4 th Dimension

Most common DBMS model on market? n Relational

The relational DBMS we will be using in the course? n Access, which is part of Microsoft Office

Two components of employing a DBMS n n Designing and building the database Manipulating the data

Steps in building a database n n n Choose a DBMS Define the data structure (Data Definition) Create or import a set of records

Steps in using a database n Data Manipulation: n n n n Insert Retrieve Update Delete Sort Calculate, etc. Recovery, Security, etc.

Building a database n n n In the relational data model a database consists of one or more tables. (Each table is called a relation, hence the name relational. ) Each row in one of these tables is a record. A record consists of a set of fields.

What is a database schema? n n A database schema consists of all the information about what the tables are, what the fields are within each record in each table, how the tables are related, etc. If you take an existing database and delete all the records, what’s left is the underlying database schema.

n n So the first step in building a new database is to create the underlying database schema. A major component of this is to tell the DBMS what the structure of your records will be (Data Definition) within each table.

There are three main steps in data definition n Naming each field in a prototypical record, Specifying its datatype, and Specifying its size, if appropriate.

Data validation n n One of the main features of a DBMS is to perform data validation when a user attempts to create a new record or modify an existing record. The reason for specifying a datatype for a field is to allow the DBMS to check the validity of user-entered data and reject invalid data.