Your SlideShare is downloading. ×
0
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Database Modelling Concepts - Chapter 1
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Database Modelling Concepts - Chapter 1

1,491

Published on

Chapter-1 …

Chapter-1

For more:
Visit @
www.ebooksadda.in
www.technotz.info

Published in: Education, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
1,491
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
74
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Chapter 1 Introduction - www.EbooksAdda.in - 1
  • 2. Introduction Definition A database management system (DBMS) is a general-purpose software system that facilitates the process of defining, constructing, and manipulating databases for various applications. Definition A database is a collection of related data. Definition Data are known facts that can be recorded and that have implicit meaning. Definition File processing systems are business computer systems which store groups of records in separate files & used to process business records & produce information. - www.EbooksAdda.in - 2
  • 3. Introduction DBMS File Processing Systems Data redundancy & inconsistency Reduced by ensuring a physical piece of data is available to all programs Data is often duplicated causing higher storage and access cost, poor data integrity, and data inconsistency Accessing data Allow flexible access to Allow pre-determined access data (e.g., using queries to data (i.e., complied programs); for data retrievals) application programs are dependent on file formats Concurrent access Designed to coordinate multiple users accessing the same data at the same time Designed to allow a file to be accessed by two programs concurrently only if both programs have read-only access to the file Data security & integrity High, enforced Loose, not enforced - www.EbooksAdda.in - 3
  • 4. Data Abstraction Provides an abstract view of data Physical level: the lowest level of abstraction describes the storage structure of data. Conceptual level: the next-higher level of abstraction describes the logical structure of the database. View level: the highest level of abstraction describes part of the entire database. Many views are provides for the same database. - www.EbooksAdda.in - 4
  • 5. Database Terminology Database Schema or Conceptual View: describes the overall structure of the entire database Database Instance: describes the content of the database Scheme = Type, Instance = Value of a variable - www.EbooksAdda.in - 5
  • 6. Data Independence The capacity to change the scheme definition at one level w/o having to change the scheme definition at the next higher level Physical data independence: capacity to change the physical schema w/o having to rewrite the application programs Logical data independence: capacity to change the conceptual schema w/o having to rewrite the application programs logical data independence is more difficult to achieve than physical data independence - www.EbooksAdda.in - 6
  • 7. Data Models Describe relationships among data, data semantics, integrity & semantic constraints I. Object-Based Logic Models describe data at the conceptual & view levels DB is structured in variable-length records provide flexible structuring capabilities allow explicit specifications of data constraints widely used data models: Entity-Relationship & Object-Oriented II. Record-Based Logical Models describe data at the conceptual & view levels DB is structured in fixed-format records of different types three widely used data models: Relational, Hierarchical, & Network. - www.EbooksAdda.in - 7
  • 8. Entity-Relationship (E-R) Model An Object-Based Model A graphical structure (Chapter 2) Widely used in database design Consists of real world objects called entities & relationships among entities An entity is an distinguishable object w/ a set of attributes Entity set is a set of entities of the same type Relationship set is a set of relationships of the same type Mapping cardinalities represent the associations among different entities - www.EbooksAdda.in - 8
  • 9. An Entity-Relationship Diagram FNAME FACULTY 1 DEPT ADVISES ID# n SNAME STUDENT ADDR MAJOR n n HAS_TAKEN IS_TAKEN m m COURSE COURSE# CRHRS - www.EbooksAdda.in - 9
  • 10. An Entity-Relationship Diagram FNAME FACULTY DEPT ADVISES ID# SNAME STUDENT ADDR MAJOR HAS_TAKEN IS_TAKEN COURSE COURSE# CRHRS - www.EbooksAdda.in - 10
  • 11. The Object-Oriented Model An Object-Based Model Object identity (object-based) vs. value identity (record-based) A collection of objects w/ unique identities Objects can be simple/complex Objects can be made up of other objects Objects contain methods, codes operated on objects An operation/function that can be performed on objects of particular classes Provide “public interface” for objects of a particular class Classes consist of objects Correspond to abstract data type (ADT) Users can define their own classes Only way to operate on an object by means of operators defined Message passing for accessing data in different objects - www.EbooksAdda.in Apply a given method to a given object by sending11message a
  • 12. Object-Oriented Model Object-Oriented term Programming term Object Variable Class Type Method Function Message Call Class hierarchy Type hierarchy - www.EbooksAdda.in - 12
  • 13. Object-Oriented Database Systems Employee PersonName first String Ray last EmpName String Ross SmallInteger SSNo 11122333 HomeAddress Address stNumber SmallInteger 1055 street String Alameda city Salary Figure. An employee object. String Gresham SmallInteger 45558 - www.EbooksAdda.in - 13
  • 14. The Relational Model A Record-Based Model Data are organized & stored into 2-dimensional tables (called relations) Flexible to use and easy to understand A relational database scheme consists of a number of relation schemes of the form R(A1, A2, …, An), where R is a relation name and Ai, 1 < i < n, is an attribute name. - www.EbooksAdda.in - 14
  • 15. The Relational Model Relational term Informal equivalents Relation Table Tuple Row/Record Cardinality # rows Attribute Column/Field Degree # columns Domain Set of legal values Primary key Unique identifier - www.EbooksAdda.in - 15
  • 16. The Relational Database Model NAME S# STATUS CITY London Paris etc. Domains Primary Key S Relation S# SNAME S1 S2 S3 S4 S5 STATUS Smith Jones Blake Clark Adams 20 10 30 20 30 CITY London Paris Paris London Athens Tuples Attributes Degree - www.EbooksAdda.in - 16 C a r d i n a l i t y
  • 17. Data Definition Languages (DDL) & Data Manipulation Languages (DML) DDL Declares the DB schema and compiles the schema into tables DML Access/Manipulate (retrieve, insert, delete, & modify) the DB Procedural (or descriptive): specify what is needed & how to get it Non-procedural (or declarative): specify what is needed but not how to get it - www.EbooksAdda.in - 17
  • 18. Thank You ! For More: Visit Us @ www.ebooksadda.in www.technotz.info - www.EbooksAdda.in - 18

×