1. Define the term Database Management System.
2. Aware of the different components of a Database Management System.
3. Recognise the difference between logical and physical views of database data.
4. Define three database models and outline their basic features.
- A database management system (DBMS) is a program that provides access to all data in the database. It sits between all the programs and the stored data. A DBMS manages security and user access, maintains the integrity of stored data, and recovers information when the system fails. A range of tools provide users with the ability to perform functions such as maintain data, search, sort, display and print.
- Four components of a DBMS are:
- Data Model
- The data model defines the way data are conceptually structured. Examples include the hierarchical, network & relational models.
- Data Definition Language (DDL)
- A set of statements defining what types of information are in the database and how they will be structured, is known as the DDL. It acts as a link between between the logical and the physical views of the database. A DBMS user defines schemas and sub-schemas with the DDL. The schema is the logical description of the entire database and the listing of the data items and the relationships among them. A sub-schema is the specific set of data required by an application / user group.
- Data Manipulation Language (DML)
- To query the contents of the database, the DML is used. It allows users to retrieve, sort, display and delete the contents of a database.
- Data Dictionary
- Besides listing the standard data name and aliases for the element, the dictionary lists the names that reference this element in specific systems and identifies the individuals, business functions, applications, and reports that use the data element. Data dictionaries are advantageous for organisations in several ways including reduced data inconsistency, faster program development, and easier data modification.
- Users from all functional areas should assist in creating the logical design to ensure that their needs are identified and addressed. The logical design shows an abstract model of the data structures and arrangements to meet an organisations information needs. Identifying relationships among different data and grouping them is an integral part of developing the logical design.
Starting from the logical design, the physical design adds fine tuning for performance and cost considerations. For example, improved response time, reduced storage space, lower operating costs, etcetera.
- The structure of the relationships in most databases follow one of three models:
- Hierarchical – Early mainframe DBMS packages used a treelike structure. From the single root element, one can follow the branches of one-to-many relationships to reach the desired data element.
- Network – This model allows many-to-many relationships. Unlike the hierarchical model, the network model can access a data element by following one of several paths.
- Relational – Data elements are stored in simple tables, each record having a unique primary key. Inclusion of a foreign table’s primary key, a foreign key, can bind the relation.
A data model is a diagram of the data entities and their relationships. Data modelling usually involves understanding specific business problems and analysing the data and information to deliver a solution. With Entity-Relationship (ER) diagrams, individuals building a database have a blueprint to ensure relationships among data entities are correctly structured. ER diagrams also ensure that application programs are developed consistent with business operations and user needs.
