Db Concepts1
- 1. Database concepts Database Container for data Repository for storing organized information in the form of files MG/DB CONCEPTS/CL12
- 2. DATABASE MANAGEMENT SYSTEM software package that handles the database interface between the user and the database organizes data as a data model - infrastructure of data organization MG/DB CONCEPTS/CL12
- 3. Relational Data Model data is organized in the form of rows and columns as in a table Table - referred to as a relation Rows - referred to as tuples / records Columns - referred to as fields / attributes MG/DB CONCEPTS/CL12
- 4. Primary key A field or a group of fields that is the unique identifier for a table The primary key uniquely identifies each row of the table It contains unique value for each record MG/DB CONCEPTS/CL12
- 5. Database is a collection of related files Tables consist of organized related information Each table is a collection of records Each record contains info about a specific entity The info in each record is contained in fields A field is the basic unit of a db A field can contain text, numbers, dates or even photographs MG/DB CONCEPTS/CL12
- 6. A data base system has 2 parts The back end The front end Front-end interfaces with the user Eg> Visual Basic The back-end holds data Eg> IBM DB2, MS SQL Server, Oracle, Sybase, Informix, MS Access, Ingress etc MG/DB CONCEPTS/CL12
- 7. Structured Query Language(SQL) Enables you to create, operate and control relational databases Used for defining and manipulating relational databases Non-procedural language Format free language (Tabs, carriage return and spaces can be included anywhere in the statement) Case insignificant MG/DB CONCEPTS/CL12
- 8. The language consists of the following components: Data definition component/language: Consists of commands that define and destroy objects like relations/tables, indexes, views etc Eg> Create, alter, drop etc Data manipulation component/language: Consists of retrieval, manipulation and update directives Eg> select, insert, delete, update etc MG/DB CONCEPTS/CL12
- 9. Data control component: Used for defining security and access control of the database. Allows the user to grant access privileges. Eg> grant : to grant privileges to other users revoke: to revoke privileges The commands are also known as Transaction control commands Transaction control language commands : Manage changes made by DML commands. Commit : to make the changes permanent MG/DB CONCEPTS/CL12 Rollback: to undo all changes.
- 10. SQL statements can be executed directly i.e interactively or as part of an application program Interactive SQL : Used to operate directly on a db to produce the required output. Used by non-programmers MG/DB CONCEPTS/CL12
- 11. Embedded SQL : SQL statements embedded within the program source code that is written in some programming language / front end tool Used by programmers MG/DB CONCEPTS/CL12
- 12. Terminology Cardinality : The number of tuples is called the cardinality Degree : The number of attributes is called the degree Domain a pool of values from which specific attributes of specific relations draw their values. just a data type; provides a set of values from which various attributes in various relations take their actual values. MG/DB CONCEPTS/CL12
- 13. Primary key : a column or a group of columns in a table that uniquely identifies records in the table. unique identifier for the table. contains unique value for each record. Candidate key : Attributes in a relation that can serve as primary key are candidate keys as they are candidates for the primary key position. MG/DB CONCEPTS/CL12
- 14. Alternate key : A candidate key that is not the primary key is called an alternate key. Foreign key : Column or a group of columns in a table that is used to reference a primary key in another table. MG/DB CONCEPTS/CL12
- 15. Terminology MG/DB CONCEPTS/CL12