INF2603 STUDY NOTES SUMMARY.

INF2603 STUDY NOTES SUMMARY. Chapter 1: Database Systems Data: Raw facts Information: The result of processing raw data to reveal its meaning. Knowledge: The body of information and facts about a specific subject. Data Management: A discipline that focuses on the proper generation, storage and retrieval of data. Database: A shared, integrated computer structure that stores a collection of: • End-user data or raw facts of interest to the end user. • Metadata or data about data, through which the end-user data are integrated and managed. DBMS (Database management system): A collection of programs that manage the database structure and controls access to the data stored in the DB. Data Inconsistency: Exists when different versions of the same data appear in different places. Query: A specific request for data manipulation. Done through the DBMS. Types of databases Single User DB: Supports only one user at a time. It runs on a PC and is called a desktop DB. Multiuser DB: Supports multiple users at the same time, when it has a small user base it is called a workgroup DB, if it supports more than 50 users it is called an enterprise DB. Centralised DB: A DB that supports data located at a single site. Distributed DB: A DB that supports data distributed across several different sites. Operational DB: A DB that is designed primarily to supports a company’s day to day operations. (AKA Transactional DB, Production DB) Data Warehouse: Focuses on storing data used to generate information required to make tactical or strategic decisions. Why DB design is important DB Design: Refers to the activities that focus on the design of DB structure that will be used to store and manage end user data. Historical Roots: Files and File Systems Basic file terminology: Field: A character or group of characters that has a specific meaning. A field is used to define and store data. Record: A logically connected set of one or more fields that describe a person, place or thing. File: A collection of related records. Limitations of file system data management: • Requires extensive programming. • There are no ad hoc query capabilities. • System admin can be more complex and difficult. • It’s difficult to make changes to existing structures. • Security features are likely to be inadequate. Structural and Data dependence: Structural Dependence: Access to a file is dependent on its structure. Structural Independence: Exists when it’s possible to make changes in the file structure without affecting the application program’s ability to access the data. Data Dependence: Because all data access programs are subject to change when any of the file’s data storage characteristics change the file system is said to exhibit data dependence. Data Independence: Exists when it is possible to make changes in the data storage characteristics without affecting the application program’s ability to access the data. The practical significance of data dependence is the difference between the logical data format (how the human views the data) and the physical data format (how the computer sees the data). Data dependence makes the file system extremely cumbersome from a programming and data management point of view. Data Redundancy Islands Of Information: The storage of the same basic data in different locations. This means some variations of the same data can also be saved. Data Integrity: The condition in which all of the data in the DB are consistent with real world events and conditions. Data Redundancy: Exists when the same data are stored unnecessarily at different places. Uncontrolled data redundancy sets the stage for: • Data Inconsistency: Exists when the same data are stored unnecessarily at different places. • Data Anomalies: Occurs when all of the required changes in the redundant data are not made successfully. Types of anomalies: Update, Insert, Delete. Database Systems The database system environment Fig 1.6 P21 – Contrasting database and file systems. Database system: Refers to an organization of components that define and regulate the collection, storage, management and use of data within the DB environment. It is comprised of 5 parts: • Hardware • Software • People • Procedures • Data DBMS Functions A DBMS performs several important functions that guarantee the integrity and consistency of the data in the DB: • Data Dictionary Management: The DBMS stores definitions of the data element and their relationships (metadata) in a data dictionary. • Data Storage Management: The DBMS creates and manages the complex structures required for data storage, thus relieving you of the difficult task of defining and programming the physical data characteristics. • Data Transformation and Presentation: The DBMS transforms entered data to conform to required data structures.