What is “Data”?
► A representation of raw facts which has no meaning assigned ► Generally, operations are performed on data or data items to supply some information about an entity.
What is a Database?
A database is an integrated and structured collection of stored operational data used (shared) by application systems of an enterprise
Examples of Databases
• Medical records
• Bank accounts
• Stock control
• Telephone directories
• Stock market prices
Universe of Discourse
A database is a model of some aspect of the reality of an organisation. It is conventional to call this reality a universe of discourse (UOD), or sometimes a domain of discourse.
– Naïve or casual user
– Accesses database either through forms or through application front-ends – More sophisticated ones generate ad hoc queries using DML
– Designs and implements applications that access the database (some may be used by end users) –
Database administrator (DBA)
– Defines and manages the conceptual schema
– Defines application and user views
– Monitors and tunes DBMS performance (defines/modifies internal schema) – Loads and reformats the database
– Responsible for security and reliability
Data Dictionary – Metadata
• The dictionary or catalog stores information about the database itself • This is data about data or ‘metadata’
• Almost every aspect of the DBMS uses the dictionary
The dictionary holds:
• Descriptions of database objects (tables, users, rules, views, indexes,…) • Information about who is using which data (locks) • Schemas and mappings
A database Management System
A database management system (DBMS) is an organised set of facilities for accessing and maintaining one or more databases. A DBMS is a shell which surrounds a database or series of databases and through which all interactions take place with the database.
• A database system consists of
• Data (the database)
• We focus mainly on the data
• Database systems allow users to:
• Protect their data.
Formalism that defines what the structure of the data is
– Within a file
– Between files
File systems can at best specify data organization within one file Alternatives for business data
– Hierarchical; network
This structure is usually called the schema
– A schema can have many instances
Types of DBMSs
► Network – data model based on graphs with records as nodes and relationships between records as edges ► Hierarchical – data model based on trees
► Relational – data model based on tables
► Object-Oriented – data model based on the object-oriented programming paradigm ► Distributed – composed of several independent DBMSs running at the nodes of a communications network Database Development Methodology steps
• Requirements elicitation involves establishing the key technical requirements for a data base system usually through interaction between developers and users • It determines the scope of universe of discourse to be covered by the proposed database system
Conceptual Data Modelling
It involves building data model of the real world that is expressed in terms of data requirements established The most popular approaches for to conceptual modelling Include: 1. Entity Relationship Diagramming
This is used to construct an entity model which is of UOD in terms...
References: state (country_code, state_code);
Dropping a Table
■ To remove the definition of a table from the data dictionary, you have to use the drop table command. The format of this is Dropping (deleting) a Table
drop table tablename;
Second Normal Form
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