Introduction to Databases Angela Clark University of South Alabama

University of South Alabama - CIS Databases Used to store electronic information Referred to as secondary storage We will discuss  Benefits for using databases  Database Management Systems  Different database structural formats

University of South Alabama - CIS Benefits of Databases Data Sharing – information in one department can be readily shared with other departments Security – users can be given passwords and/or access only to the kind of information they need to know while containing all of the information in the same database file Data Redundancy – fewer files are necessary; data is stored only once and in one location. This reduces the storage space needed. Data Integrity – Changes made in the database will update all occurrences

University of South Alabama - CIS Database Management Systems DBMS - special software that allows you to create, modify, and gain access to a database data dictionary - contains a description of the structure of the data used in the database; defines field names, type of data that can go into the field, the size of the field, and defines which field is the key field query language - allows access to information in the database; most widely used query language is SQL (structured query language)

University of South Alabama - CIS Database Organization Most common types of database formats are:  Hierarchical Database  Network Database  Relational Database  Object Oriented Database

University of South Alabama - CIS Hierarchical Databases Structured in nodes (tree like structure) Each child node has one and only one parent node (a parent may have more than one child node). We refer to this as a 1-to-many relationship. Progress top down to traverse fields. To find information, you must start at the top with a parent node and trace down the tree. Use pointers to connect parent node to child nodes.

University of South Alabama - CIS Hierarchical Databases Advantages of Hierarchical Databases:  Efficient and easy to create Disadvantages of Hierarchical Databases:  If a parent node is deleted, so are all child nodes  Cannot add a child node without adding all parent nodes first  Low flexibility – paths and directories to information must be specified in advance; very difficult to change  Difficult to maintain

University of South Alabama - CIS Network Databases Variation on the hierarchical database to reduce data redundancy Child nodes can have more than one parent (many-to-many relationship) Nodes are reached through pointers; may provide more than one path to same information

University of South Alabama - CIS Network Databases Advantages of Network Databases:  Efficient  Faster than hierarchical  Less data redundancy Disadvantages of Network Databases:  Low flexibility  More pointers; the number of pointers increases rapidly, which makes it much more complicated to maintain and operate.

University of South Alabama - CIS Relational Databases The most flexible – it is not hierarchical in nature Uses tables made up of columns and rows  Columns correspond to Fields  Rows correspond to Records Related tables can be linked together through Common Data Elements (keys, foreign keys)

University of South Alabama - CIS Relational Databases Advantages of Relational Databases:  Simple to add, delete, and edit; there are no pointers  It can relate data in one field in one table to another field in another table  Flexible – ad hoc queries can combine data from different sources Disadvantages of Relational Databases:  Slower – may require multiple access to the data  Requires some data redundancy in order to be more efficient - the same data must appear in multiple tables to link the tables  Must remember to change/update all tables

University of South Alabama - CIS Object Oriented Databases  Handles unstructured data such as photographs, graphics, audio, video, etc.  Keep track of objects – both data and the action that can be taken on the object.

University of South Alabama - CIS Types of Databases Individual – collection of files primarily used by just one person Company/Shared – databases that can be used by multiple users, shared through local area networks Distributed – data for the database is stored in multiple locations with access through communication networks Proprietary – an enormous database developed to cover particular subject areas; usually offers access to people for a fee – databanks.

University of South Alabama - CIS Questions