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What is Data? What is the difference between Data and Information? Examples of a Database: •Student Records at UCC •Credit Card details •Directory Enquiries •Insurance Broker •Library System What is data? What is data? Data is the raw material from which information is obtained The processing of data consists of manipulating it into a form which provides information in a format that is meaningful and usable to the manager or other end-user Arrival of computer processing meant this process was ‘mimicked’. Automation of existing systems. This is a traditional file-based system History of Information: Initially the information needs of an organisation were met using a ‘manual system’. This system was very labour intensive. With the arrival of computers, the manual filing system was moved on to a computer. This early use of computers for gathering information was called the ‘file based approach’. What is a file-based system? “A collection of application programs that perform services for the end-users such as the production of reports. Each program defines and manages its own data.” (Connolly & Begg) An early attempt to computerise the manual filing system used The operation of these systems closely resembles that of a manual system. All that is really achieved is the automation of the existing system. File Based Approach APPLICATIONS PAYROLL PROGRAM ADMIN. PROGRAM PROJECT SCHEDULING PROGRAM DATA HELD RESPONSIBILITY HELD Employee Name, Age, Address, Hours, Pay Rate Payroll Dept. Dept. Name, Employee Name, Emp. Address, Office Location Dept. Managers Project Name, Start Date, Staff Name, Staff Address, Project Hours Project Leaders What are the limitations of the file-based system? Separation and isolation of data Decentralised data makes cross-referenced searching slow and difficult Duplication of Data Wastes time and money for entering and storage, leads to corruption of data integrity Program-Data Dependence What are the limitations of the file-based system? Incompatibility of files Structure and format is dependent on the development language and platform of the application Fixed queries and proliferation of application programs Ad Hoc querying and reporting code to be written from scratch What is a Database? “a shared collection of logically related data (and a description of this data), designed to meet the information needs of an organisation” (Connolly & Begg) Implications? Centralised (minimal duplication), selfdescribing (program independent to an extent), logical structure (entities, attributes and relationships). Advantages of a Database: Data Integrity is easier to maintain as all data is held in on central location A database system allows for ad-hoc queries and caters to complex questions involving the interaction and relationships between the various data items in the database to be investigated Security Minimisation of data duplication Control of data redundancy Improved Maintenance Disadvantages of a Database: Complexity – increased functionality means the system is more complex and sophisticated in structure Size – complexity and functionality makes the DBMS a large piece of software, taking up a lot of space Cost of DBMSs – the cost can vary depending on functionality required and the environment Additional Hardware Costs Cost of Conversion - conversion of existing systems High Impact of Failure - as a result of centralisation What is a DBMS? The DBMS is a piece of software whose main function is to organise data so it can be retrieved, modified or updated at will. It is the link between the user and the data, giving access to the data required for the systems and their application programs. “A software system that enables users to define, create, and maintain the database and provides controlled access to this database” (Connolly & Begg). Database Management System APPLICATIONS DATA HELD PAYROLL PROGRAM Database ADMIN. PROGRAM PROJECT SCHEDULING PROGRAM DBMS Employee Administration and project Details Explanation of a DBMS In the database structure, each system draws its data via the database management system, so each system’s program interacts with the DBMS rather than the database files themselves (e.g MS Access) A DBMS can be described as an intelligent filing cabinet, as it performs all the functions of an efficient filing clerk Components of a DBMS: Data definition language is used to define the database (types, structure and constraints) Data Manipulation Language is used to insert, update, delete and retrieve data. Utilises a flexible, ad hoc, query language There are two types of query language, procedural (one record at a time, “specifies how”) and nonprocedural (sets of records, “specifies what”). Access control includes security, integrity, concurrency, recovery and catalogues. Components of a DBMS: End-users use VIEWS which makes the DBMS transparent in its activities A DBMS consists of hardware (machines, network connections, physical storage), software (OS, DBMS, applications), data, procedures and people (administrators, designers (logical and physical), programmers and end-users. Advantages: Less redundancy, improved consistency, information, integrity, security, scalability, flexibility, productivity, concurrency, maintenance and recovery. Disadvantages: complexity, size, cost, generalisation, high impact of failure. Roles in Database Management System • • • • Database Administrator Database Designers Application Programmers End-Users Architecture Most DBMS’s use a three-level architecture: External, Internal and Conceptual Internal - describes how the data is stored in the database (space allocation, compression, encryption etc.) and interfaces with the OS to manage files in physical storage Conceptual - Describes what data is stored and the relationships between data External - Defines the users view of the data Reasons for Three-Tier Architecture