Unit 5
Databases



Conceptual data model - describes how data elements in the system are to be grouped


Entity - thing of interest about which data is to be held


Attribute - property or characteristic of an entity


Relationship - link or association between entities


Entity-relationship diagram - diagrammatic way of representing the relationship between the entities in a database


Problems with the traditional file approach:-


Database - collection of non-redundant data sharable between different applications


Problems with the database approach:-


Database Management System (DBMS)


Relational database


Foreign key - primary key from one table used as foreign key in a second table (common field)


Normalisation


First normal form - no repeating attributes or groups of attributes


Second normal form - in first normal form and no attribute that is not part of the primary key is dependent on only a portion of the primary key


Third normal form - no non-key dependencies (Boyce-Codd Normal Form - BCNF)



SQL (Structured Query Language) - data access language which deals with the manipulation of tables and data


DML (Data Manipulation Language) - the part of SQL concerned with asking questions of a database


Schema - different levels or views from which a database may be considered



DDL (Data Definition Language)


DML (Data Manipulation Language) - provides comprehensive set of commands to allow modification of the data within a database

VALUES ('Harry', 'Washington', 'Trainee')


Open systems - provide a standard by which applications may be written to allow portability to multiple systems


OBDC (Open Database Connectivity)


Database Mnagement System (DBMS)


Data dictionary - a database about the database


Multi-access database - more than one person can view and update the same tables concurrently


Ensuring integrity - ensuring no data is lost or corrupted (making sure updates are not lost)


Deadlock (Deadly embrace)


Software protection techniques


Client-server database


Object-oriented database - stores the data and methods as objects that can be automatically retrieved and shared (more suited to handling graphics based or multimedia applications)