chapter 3Introduction to Database System.ppt

chapter 3Introduction to Database System.ppt

• 1.
  Company LOGO chapter3 chapter3 Introduction Introduction to DatabaseSystem to Database System
• 2.
  Learning Objective ⚫Define DatabaseManagement System (DBMS) and database ⚫ Describe the advantages and disadvantages of DBMS to file based system. ⚫Analyses structure models in Database
• 3.
  Definitions Database: ⚫A very large,integrated collection of data. ⚫Models real-world enterprise. ⚫ Entities (e.g., students, courses) ⚫ Relationships (e.g., Madonna is taking CS564) Database Management System (DBMS) ⚫a software package designed to store and manage databases. . Examples of Database Applications: • Banking: all transactions • Airlines: reservations, schedules • Universities: registration, grades
• 4.
  Purpose of DatabaseSystems ⚫ In the early days, database applications were built directly on top of file systems ⚫ Drawbacks of using file systems to store data: ⚫ Data redundancy and inconsistency ⚫ Multiple file formats, duplication of information in different files ⚫ Difficulty in accessing data ⚫ Need to write a new program to carry out each new task ⚫ Data isolation — multiple files and formats
• 5.
  ⚫ Concurrent accessby multiple users ⚫ Concurrent accessed needed for performance ⚫ Uncontrolled concurrent accesses can lead to inconsistencies ⚫ E.g. two people reading a balance and updating it at the same time. ⚫ Security problems ⚫ Database systems offer solutions to all the above problems Purpose of Database Systems
• 6.
  ⚫ Separation ofthe Data definition and the Program ⚫ Abstraction into a simple model ⚫ Data independence and efficient access. ⚫ Reduced application development time – ad-hoc queries ⚫ Data integrity and security. ⚫ Uniform data administration. ⚫ Concurrent access, recovery from crashes. Why Use a DBMS?
• 7.
  Why Study Databases?? ⚫Shift from computation to information ⚫ Datasets increasing in diversity and volume. ⚫ Digital libraries, interactive video ⚫ ... need for DBMS exploding ⚫ DBMS encompasses most of CS ⚫ OS, languages, theory, AI‫و‬ ,multimedia , logic ?
• 8.
  Levels of Abstraction ⚫Many views, single conceptual (logical) schema and physical schema. ⚫Views describe how users see the data. ⚫Conceptual schema defines logical structure. Sometime we separate between conceptual level and logical level. ⚫Physical schema describes the files and indexes used. * Schemas are defined using DDL (Data Definition Language) *data is modified/queried using DML (Data Manipulation Language). Physical Schema Conceptual Schema View 1 View 2 View 3
• 9.
  Levels of Abstraction ⚫Physical level: describes how a record (e.g., customer) is stored. ⚫ Logical level: describes data stored in database, and the relationships among the data. type customer = record customer_id : string; customer_name : string; customer_street : string; customer_city : string; end; ⚫ View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
• 10.
  Instances and Schemas ⚫Schema – the logical structure of the database ⚫ Example: The database consists of information about a set of customers and accounts and the relationship between them) ⚫ Analogous to type information of a variable in a program ⚫ Physical schema: database design at the physical level ⚫ Logical schema: database design at the logical level ⚫ Instance – the actual content of the database at a particular point in Time.
• 12.
  Data Models ⚫ Acollection of tools for describing ⚫ Data ⚫ Data relationships ⚫ Data semantics ⚫ Data constraints ⚫ Relational model ⚫ Entity-Relationship data model (mainly for database design) ⚫ Object-based data models (Object-oriented and Object- relational) ⚫ Semistructured data model (XML) ⚫ Other older models: ⚫ Network model
• 13.
  Data Manipulation Language(DML) ⚫ Language for accessing and manipulating the data organized by the appropriate data model ⚫ DML also known as query language ⚫ Two classes of languages ⚫ Procedural – user specifies what data is required and how to get those data ⚫ Declarative (nonprocedural) – user specifies what data is required without specifying how to get those data ⚫ SQL is the most widely used query language
• 14.
  Data Definition Language(DDL) ⚫ Specification notation for defining the database schema Example: create table ( account ( account_number char(10) branch_name char) 10 ( balance integer (10). DDL compiler generates a set of tables stored in a data dictionary.
• 15.
  ⚫ Data dictionarycontains metadata (i.e., data about data) ⚫ Database schema ⚫ Data storage and definition language ⚫ Specifies the storage structure and access methods used ⚫ Integrity constraints ⚫ Domain constraints ⚫ Referential integrity (e.g. branch_name must correspond to a valid branch in the branch table)
• 16.
  SQL ⚫ SQL :widely used non-procedural language ⚫ Example: Find the name of the customer with customer-id 192-83-7465 select from where customer.customer_name customer customer.customer_ id = ‘192-83- 7465’ ⚫ Application programs generally access databases through one of : ⚫ Language extensions to allow embedded SQL ⚫ Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database
• 17.
  Database Design The processof designing the general structure of the database: ⚫Logical Design –Deciding on the database schema. Database design requires that we find a “good” collection of relation schemas. ⚫ Business decision – What attributes should we record in the database? ⚫ Computer Science decision –What relation schemas should we have and how should the attributes be distributed among the various relation schemas? ⚫Physical Design – Deciding on the physical layout of the database
• 18.
  The Entity-Relationship Model ⚫Models an enterprise as a collection of entities and relationships ⚫ Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects ⚫ Described by a set of attributes ⚫ Relationship: an association among several entities ⚫ Represented diagrammatically by an entity-relationship diagram:
• 19.
  The End Thank you 19