Db Concepts2
- 1. DATABASE CONCEPTS DATABASE An electronic filing cabinet A repository for a collection of computerized data files A collection of persistent data that is used by the application system of some given enterprise The term enterprise is a generic term for any self-contained commercial, scientific, technical or other organization MG/DB CONCEPTS/CL12
- 2. DATABASE SYSTEM A computerized record-keeping system. A database system involves four major components: data, hardware(secondary storage devices, processor(s) and associated main memory etc.,), software(the DBMS) and users(application programmers, end users, database administrator). MG/DB CONCEPTS/CL12
- 3. Data independence The ability to modify the scheme definition in one level without affecting the scheme definition in the next higher level is called data independence. Physical data independence : refers to the ability to modify the scheme followed at the physical level without affecting the scheme followed at the conceptual level i.e., the application programs remain the same even though the scheme at physical level gets modified. Logical data independence : refers to the ability to modify the conceptual scheme without causing any changes in the schemes followed at view level. MG/DB CONCEPTS/CL12
- 4. Data models The hierarchical model The network model The relational model MG/DB CONCEPTS/CL12
- 5. The hierarchical model The oldest model and is popular on main frames Represents data by a collection of records organized in the form of a tree structure Relationships among data are represented by links The record at the top of the tree is the root The hierarchy is maintained in the form of nodes and branches The root may have any number of dependents, each of these dependents may have any number of lower level dependents and so on to any number of levels MG/DB CONCEPTS/CL12
- 6. Consider a student course-marks database. In the hierarchical model, a student can register for many courses and get marks for each course. Scode Sname Scode Sname S2 B S1 A Ccode Cname Marks Ccode Cname Marks C1 Physics 65 C3 Maths 83 C2 Chemistry 78 C4 CompSc 85 C3 Maths 83 C4 CompSc 85 MG/DB CONCEPTS/CL12
- 7. The student record is called as root. It has got a course-marks record that is called the child record. A parent can have many children. A child cannot have more than one parent and no child can exist without its parent. In this type of model following possibilities exist. Insert : Since no child record can exist without its parent, it is not possible to insert a new course details without introducing a dummy student Delete : If a course is selected by only one student, then deleting that student will automatically delete all info about the course Update : To change the course name of one course, the whole database has to be searched. This may result in data inconsistency. MG/DB CONCEPTS/CL12
- 8. The network model A NW model represents data by a collection of records and relationships among data are represented by links. The student and course records are linked together through a marks record. There are no restrictions on number of parents. A record type can have any number of parent and child record types. It is more complex than the hierarchical model because of links. It can represent any structure designed in hierarchical model, and so is a superset of the hierarchical model. MG/DB CONCEPTS/CL12
- 9. In network model following possibilities exist: Insert Inserting a course record or student record poses no problems as they can exist without any connectors till a student takes the course. Delete Deleting any record automatically adjusts the chain. Update Update can be done only to a particular child record MG/DB CONCEPTS/CL12
- 10. The relational model Developed by Codd In relational model, data is organized into tables consisting of rows and columns The table is referred to as a relation, the rows as tuples/records and columns as fields/attributes A row in a table represents a relationship among a set of values Since a table is a collection of such relationships, it is referred to as a relation The relationships among data are represented by a collection of tables. MG/DB CONCEPTS/CL12
- 11. Student table Marks table Scode Sname Ccode Scode Marks S1 A S2 B C1 S1 65 C2 S1 78 C3 S1 83 Course table C4 S1 85 C3 S2 83 Ccode Cname C4 S2 85 C1 Physics C2 Chemistry C3 Maths C4 Compsc MG/DB CONCEPTS/CL12
- 12. Characteristics of a relation There are no duplicate tuples Tuples are not ordered Attributes are not ordered All attribute values are atomic MG/DB CONCEPTS/CL12
- 13. 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. A domain is just a data type It provides a set of values from which various attributes in various relations take their actual values. MG/DB CONCEPTS/CL12
- 14. Primary key A column or a group of columns in a table that uniquely identifies records in the table. It is a unique identifier for the table. It contains unique value for each record. Foreign key A 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. Database concepts (Revision) A database is a container for data It is repository for storing organized information in the form of files A db management system is a software package that handles the database It is an interface between the user and the database A DBMS organizes data as a data model Data model is an infrastructure of data organization MG/DB CONCEPTS/CL12
- 16. In a Relational Data Model, the data is organized into tables consisting of rows and columns A table is referred to as a relation The rows are referred to as tuples/records The columns are referred to as fields / attributes Primary key A primary key is a unique identifier for the table It consists of one/more attributes that uniquely identify each and every record in a table It contains unique value for each record MG/DB CONCEPTS/CL12
- 17. A database is a collection of tables Tables consist of organized related information Each table consists of 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
- 18. A data base system has 2 parts The back end The frond end Front-end s/w interfaces with the user Eg> Visual Basic The back-end s/w holds data Eg> IBM DB2, MS SQL SERVER, ORACLE, SYBASE, INFORMIX, MS ACCESS MG/DB CONCEPTS/CL12
- 19. Structured Query Language(SQL) Enables you to create and operate on relational databases A relational database is a collection of tables Used for defining and manipulating relational databases Non-procedural language Format free language (Tabs, carriage return and spaces can be included anywhere in the statemen Case insignificant MG/DB CONCEPTS/CL12
- 20. The language consists of the following components: Data definition component/language: This component is used for defining and destroying objects like relations/tables, index etc Eg> Create, alter, drop Data manipulation component/language: This component is used to retrieve and modify data. It contains retrieval, manipulation and update directives Eg> select, insert/delete, update MG/DB CONCEPTS/CL12
- 21. Data control component: Used for defining security and access control of the database. Allows the user to grant access privileges. Eg> grant, revoke MG/DB CONCEPTS/CL12