Database concepts


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Database concepts

  1. 1. Introduction to Database Concepts Ucc - Mwanza. May 2006
  2. 2. Database Definition A database can be defined as collection of information organized in such a way that it can be accessed easily. Examples are  Tracking customer orders  Maintaining Employees Records.  Maintaining Students Information
  3. 3. Terminologies In studying Databases the following Terminologies must be clear Data  This is the fact or facts about specific entity (person, place or thing). Information  This is the processed facts perceived to be useful by the user. Field  This is a single item of information or data in entity. E.g. employee Name Record  This can be defined as data or group of fields about an entity. E.g. employee particulars  Subject (relation or table)  This can be defined as a collection of records that are related to a particular entity. For example, Records for all employees will make up one subject.
  4. 4. History of Databases Manual systems File Processing Systems (FPS) Database Management systems (DBMS)
  5. 5. Manual systems Structure Information can be stored in dedicated room or in separate offices. Room or office will be furnished with shelves; Different shelves will hold Records for different subjects. Records will be stored in hard flat files, each file will carry one record Each file will have a specific number to identify it. A person will use the file number to retrieve the specific file (record).
  6. 6. Manual systems User File keeper Files Cabinet
  7. 7. File Processing Systems (FPS) Information stored as groups of records in separate files File processing systems consisted of a few data files and many application programs Each file called a soft flat file Flat file contain processed information for one specific function Use of programming languages to write applications Little flexibility High maintenance Many limitations
  8. 8. Limitations of File Processing Systems Separate and isolated data Data redundancy Program - data interdependence involving file formats and access techniques Difficulty in representing data from the user’s view Data inflexibility
  9. 9. Database Management systems (DBMS) A program that allows users to define, create, manipulate, store, maintain, retrieve, and process the data in a database in order to produce meaningful information. Focus on information representation Data stored as records in various database files that can be combined to produce meaningful information for users DBMS controls all functions of capturing, processing, storing, retrieving data and generates various forms of data output Manages access by multiple users and multiple programs to a common store of data
  10. 10. DBMS overcomes all Limitations of FPS. Eliminates separation and isolation of data Reduces data redundancy Eliminates dependence between programs and data Allows for representation of data from user’s view Increases data flexibility Superior flexibility and security over spreadsheet applications
  11. 11. Characteristics of a DBMS  Computerized record-keeping system  Contains facilities that allow the user to: o Add, delete files o Insert, retrieve, update, delete data  Collection of databases; each can be used for separate purposes or combined
  12. 12. Functions and Uses of a DBMS To store data To organize data To control access to data To protect data To provide decision support To provide transaction processing
  13. 13. Advantages and Disadvantages of a DBMS • Advantages:  Centralized data reduces management problems  Data redundancy and consistency are controllable  Program - data interdependency is diminished  Flexibility of data is increased • Disadvantages:  Reduction in speed of data access time  Requires special knowledge  Possible dependency of application programs to specific DBMS versions
  14. 14. Database Administrator A database administrator (DBA) controls and manages the database. Function of a DBA Make decisions concerning the content of the database Plan storage structures and access strategies. Provides support to users Defines security and integrity checks Interprets backup and recovery strategies.
  15. 15. Types of Databases Flat Databases Hierarchical Database Network Database Relational Database
  16. 16. Flat databases A single kind of record with a fixed number of fields. a way of organizing all information in a single table. suitable for extremely simple databases. inherit data redundancy
  17. 17. Flat databases
  18. 18. Hierarchical Database Fields or records structured in nodes Viewed as branches of an upside-down tree Each item is subordinate to its parent node Only one parent per node The subordinate item is the child node to the parent If parent node is deleted, all the child nodes are as well deleted New parent node must be created before adding a new child node Limited by rigid structure No direct relationships between child nodes
  19. 19. Hierarchical Database
  20. 20. Network Database Also has hierarchical node arrangement But here child nodes may have more than one parent node, or a many-to-many relationship The interconnected design allows for access via multiple pathways
  21. 21. Network Database
  22. 22. Relational Database No pre-determined access paths Data stored in a collection of columns and rows called a table, or a relation Tables may be electronically linked via a key field containing common data Easy to add, delete and modify the data and the table structures
  23. 23. Relational Database
  24. 24. Relational Terminologies Table or Relation Null values Duplicate Values Changeable Values Primary Keys Foreign Keys
  25. 25. Table or Relation Table will store information for a particular entity Table name must be unique  The Table name should be descriptive Column Name must be unique within the Table Rows must be unique
  26. 26. Null values missing or unknown value in a column of a table Nulls are not the same as zeros Most arithmetic operations can be performed on zero values nulls must be excluded from mathematical manipulations
  27. 27. Duplicate values A duplicate value is a value in a column of a table that exactly matches some other values within the same column.
  28. 28. Changeable values value in a table that may vary over time. Most values in most tables are Changeable You can prevent changes when it is desirable to prevent changes in a given column of a table
  29. 29. Primary keys Uniquely identify each row of that table. Every table must have only one Primary key
  30. 30. Rules for Primary key Must always have a value (null values are not allowed) Value should be unique (duplicate values are not allowed) Value should not change over time
  31. 31. Foreign keys key which relates the rows of the Table to other Tables value can be null, value can change value can be duplicated
  32. 32. Rule for Foreign keys Value must refer to the existing primary key.